Synthesis and applications of novel acceptoredonoreacceptor organic dyes with
dithienopyrrole- and
fluorene-cores for dye-sensitized solar cells
Duryodhan Sahu
a, Harihara Padhy
a, Dhananjaya Patra
a, Jen-Fu Yin
a, Ying-Chan Hsu
b, Jiann-T
’Suen Lin
b,
Kuang-Lieh Lu
b, Kung-Hwa Wei
a, Hong-Cheu Lin
a,*aDepartment of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan, ROC bInstitute of Chemistry, Academia Sinica, Taipei 115, Taiwan, ROC
a r t i c l e i n f o
Article history:
Received 21 September 2010
Received in revised form 2 November 2010 Accepted 9 November 2010
Available online 13 November 2010 Keywords:
Dye-sensitized solar cell Di-anchoring dyes Acceptoredonoreacceptor Density function theory Electron lifetime
a b s t r a c t
Four novel symmetrical organic dyes (S1eS4) configured with acceptoredonoreacceptor (AeDeA) structures containing electron donatingfluorene (S1 and S2) and N-alkyl dithieno[3,2-b:20,30-d]pyrrole
(DTP) (S3 and S4) cores terminated with two anchoring cyanoacrylic acids (as electron acceptors) were synthesized and applied to dye-sensitized solar cells (DSSCs). The DSSC device based on S2 dye showed the best photovoltaic performance among S1eS4 dyes: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 76%, a short circuit photon-to-current (JSC) of 12.27 mA/cm2, an open circuit
voltage (VOC) of 0.61 V, afill factor (FF) of 0.63, and an overall power conversion efficiency (h) of 4.73%.
Besides, the utilization of chenodoxycholic acid (CDCA) as a co-adsorbent in the DSSC device based on S3 dye showed a significant improvement in itshvalue (from 3.70% to 4.31%), which is attributed to the suppression of dye aggregation on TiO2surface and thus to increase the JSCvalue eventually.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
The growing global energy demands attracted significant at-tention to develop renewable energy resources. As a renewable source of energy, DSSCs became one of the most promising low cost alternatives to conventional photovoltaics.1 After the successful exploration by Michael Gr€atzel,2,3DSSCs based on
Ru-photosensi-tizers, such as N3 and N719, have been extensively investigated and developed.4,5 So far, the Ru sensitizers have been reported with impressive solar-to-electrical power conversion efficiency values of ∼11%.4e9However, in addition to high cost of rare Ru metal, the
ruthenium dyes featuring relatively low molar extinction co-efficients and tedious purification processes,5 made scientists to
think and develop the metal-free organic sensitizers lately. In contrast to those metal sensitizers, to reach higher efficiencies of metal-free sensitizers remained a challenge and a great progress has been made in thisfield hitherto. Various metal-free organic dyes, such as coumarin,10indoline,11,12cyanine,13,14merocyanine,15 perylene,16thiophene,17andfluorene,18e20have been reported as
efficient sensitizers for DSSCs, where the higher molar extinction coefficients of metal-free organic dyes enhanced the net light harvesting.
There are numerous dyes with common structural composi-tions, i.e., an electron donor with a high absorption band in the visible range and an electron acceptor (most notably cyanoacrylic acid), which facilitate vectorial charge transfers upon light ab-sorption as well as assist the dye to anchor on the TiO2surface, and
a
p
-conjugated spacer between the donor and acceptor has been reported to enhance the charge carrier mobilities with effective intramolecular charge transfers.21However, researches on DSSC have led to a greater understanding of the key dye characteristics like, possessing high molar extinction coefficients18,19low band gaps and capable of absorbing the entire
solar spectrum that make dyes to achieve high power conversion efficiencies.22e24Most importantly, the structural configurations of
dyes that containing multiple electron acceptors followed by an-choring groups can generate photoinduced intramolecular charge transfer (ICT), which can inject electrons to the TiO2conduction
band.14,15,25e27Due to the efficient light harvesting and high molar extinction coefficients, fluorene-based compounds exhibited some significant power conversion efficiencies both in DSSC and polymer solar cell applications.18,19Rasmussen and co-workers pioneered the use of N-alkyl dithieno[3,2-b:20,30-d]pyrrole (DTP) as a promising fused aromatic building block for electronic materials.28Since then, the introduction of DTP units imparted enhanced conjugation, high conductivity, and high charge carrier mobility for electronic mate-rials, such as organic light-emitting diodes (OLEDs),29organic pho-tovoltaic devices (OPVs),30 and field effect transistors (FETs).31
* Corresponding author. Tel.: þ886 3 5712121x55305; fax: þ886 3 5724727; e-mail address:[email protected](H.-C. Lin).
Contents lists available atScienceDirect
Tetrahedron
j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / t e t
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2010.11.044
However, no attention has been paid to use this novel high conju-gated aromatic (DTP) unit in DSSC researches since its structural invention. There are still some major drawbacks for organic dyes used in DSSCs, such as the dye aggregations, poor electron lifetime and high charge recombination that hinder efficient injections of the excited dyes to the conduction bands so as to decrease the overall performances.23,32e34As a result, many efforts of using co-adsor-bents and engineering molecular structures,10a,22a,23 have been made to overcome those problems and to enhance their power conversion efficiencies.
As shown in Fig. 1, four acceptoredonoreacceptor (AeDeA) configured dyes with two different donors (fluorene and DTP cores) were designed as follows: (1) Fluorene: it enhanced the net molar extinction coefficient with different thiophene spacers17e19(2 and
3 thiophene units in S1 and S2, respectively); (2) DTP: a new (in the field of DSSC application) fused aromatic building block, enhanced absorption spectra with various thiophene spacers (1 and 2 thio-phene units in S3 and S4, respectively). The di-hexyl and branched octyl side-chains influorene (S1eS2) and DTP (S3eS4) cores, re-spectively, increased the solubility and steric hindrance of the di-anchoring dyes to adsorb on TiO2surfaces. The use of conducting
thiophene spacers and cyanoacrylic acid termini (electron accep-tors) in S1eS4 dyes gave higher absorption spectra and thus to enhance their photovoltaic parameters crucially.20,25Furthermore, to provide a clear substantiation of the electronic structures and optical properties, we performed density functional theory/time-dependent density function theory (DFT/TDDFT) through optimi-zation and calculation of their delocalioptimi-zations in HOMO/LUMO levels. Compared with DTP-based S3eS4 dyes, the DSSC containing fluorene-based S2 dye achieved the highest power conversion ef-ficiency (PCE) value (
h
¼4.83%), which was attributed to its high molar extinction coefficient (11.9104M1cm1at 484 nm),19,22though it has a shorter absorption wavelength. The predicted broader spectral response of S4 dye was not decisive for the pho-tovoltaic performance due to its shorter electron lifetime induced by the oxidized dye, which accelerated the recombination of elec-trons in TiO2surface with redox species yielding lower
photocur-rent. Moreover, chenodoxycholic acid (CDCA) as co-adsorbent was used in the sensitization processes of S2 and S3 dyes in order to overcome the negative effects of dye aggregations on TiO2surfaces
and enhance the
h
values.22a,23As a result, the overall PCE value of S3 was improved significantly (h
value increased from 3.70 to 4.31%), regardless to the negligible change in S2 dye.2. Results and discussion 2.1. Optical properties
The UVevis absorption and normalized photoluminescence (PL) spectra of dyes in THF solutions are displayed inFig. 2a and b, re-spectively, and their corresponding data are listed inTable 1. As shown in Table 1, both molar extinction coefficients of S1 (
3
¼9.20104M1cm1) and S2 (3
¼11.19104M1cm1) at theircorrespondent absorption maxima are higher than those of S3 (
3
¼7.46104M1cm1) and S4 (3
¼7.90104M1cm1), which canbe attributed to the fused phenyl rings offluorene cores18in S1 and
S2 dyes instead of the fused thiophene rings of N-alkyl dithieno [3,2-b:20,30-d]pyrrole (DTP) cores35in S3 and S4 dyes. These higher molar extinction coefficients indicate, S1 and S2 dyes bearing flu-orene cores have facilitated higher light harvesting efficiencies than S3 and S4 dyes containing DTP cores. By adding one more thio-phene unit on both sides of conjugated spacers in the symmetrical acceptoredonoreacceptor (AeDeA) structures, the increases of conjugation lengths from S1 to S2 and from S3 to S4 enhanced the molar extinction coefficients, respectively. Hence, S2 dye with the largest molar extinction coefficient has the highest light harvesting efficiency, which subsequently promotes S2 to have the best pho-tovoltaic performance among all dyes (S1eS4). Except S4 (with
Fig. 1. Molecular structures of organic dyes (S1eS4).
Fig. 2. (a) UVevis absorption, (b) Normalized PL spectra, of S1eS4 dyes (excited at 480 and 560 nm, respectively) recorded in THF solutions (concentration at 1.010‑5M).
a weak
p
ep
*transition band at 395 nm and a prominent ICT band at 564 nm), S1eS3 dyes have a single intense band at 473, 484, and 557 nm, respectively, representing the superpositions ofp
ep
*and ICT transitions (seeTable 1). An elongation of thep
-conjugation caused a smallerp
ep
*energy gap and a spectral red shift for thep
ep
*transition was expected. Thus, bathochromic shifts from S1 to S2 (11 nm) and S3 to S4 (7 nm) were observed as a result of ex-tendedp
-conjugations. Similar to the molar extinction coefficients, the maximum wavelengths (l
max) of UVevis absorption spectraincrease as the conjugation lengths enlarged from S1 to S2 and from S3 to S4 by inserting more thiophene units on both sym-metrical spacers,36which is consistent with the theoretical com-putational data (see Fig. 3b). In addition, owing to the higher effective conjugation lengths of S3eS4 dyes containing N-alkyl
dithieno[3,2-b:20,30-d]pyrrole (DTP) cores, their absorption spectra shifted to higher wavelength than those of fluorene containing S1eS2 dyes. Fig. 3a shows the absorption spectra of the organic dyes (S1eS4) on TiO2films with a thickness of 1.5
m
m and the dataare illustrated inTable 1. Compared with the absorption spectra in solutions, the blue-shifted absorption (
l
max) wavelengths on TiO2surfaces were ascribed to the deprotonation of carboxylic acid present in the dyes.37However, the spectra of the dyes were dis-tinctly broadened to longer wavelengths and such a broadening of the absorption spectra is attributable to an interaction between the dyes and TiO2 surfaces. In PL spectra, where S1eS2 excited at
480 nm and, S3eS4 at 560 nm, showed a weak emission with stokes shift in the range 80e154 nm.
2.2. Electrochemical properties
The cyclic voltammetry (CV) measurements were performed in THF solutions to investigate the possibilities of electron transfer from the excited states of S1eS4 dyes to the conduction bands of TiO2along with the dye charge regenerations, which correspond to
the HOMO and LUMO levels of the organic dyes (S1eS4), and the CV results are illustrated inTable 1. Owing to the presence of central electron donating moieties (Fluorene or DTP), all dyes showed a quasi reversible oxidation potential (Fig. 4). The HOMO levels of the dyes were in the range5.58 to 5.14 eV with respect to I/I3
redox couple (4.60 eV vs vacuum), thus the low energy levels of dyes ensured negative Gibb’s energies and thus provided enough driving forces for the charge regenerations.23,38However, compa-rably the high energy level (5.14 eV), i.e., the low oxidation po-tential, of S4 dye hindered its effective charge regeneration and recaptured the injected electrons by the dye cation radical.37The deduced LUMO levels were in the range of ca.3.33 to 3.6 eV, which are higher than the conduction band edge (4.0 eV vs vac-uum), thus indicating that the electron injection process is ener-getically favorable. To gain an insight into the electronic states of these dyes, a DFT calculation has been performed using B3LYP hy-brid functional and 6-31G*basis sets. As shown inFig. S1 of the Supplementary data, the HOMO levels of S1 and S2 dyes are mainly delocalized on the central electron donating moieties (Fluorene) and the LUMO levels are on the cyanoacrylic acid an-choring units. In addition, there were overlappings of both HOMO and LUMO levels in the
p
-bridged thiophene units. According to Franck condon principle, these overlappings of both HOMO and LUMO levels in thep
-bridged thiophene units enhance the elec-tronic transition dipole moments between vibrational energy levels.39In general, it revealed that the HOMO to LUMO excitations moved the electron density distribution from central electron do-nating units (Fluorene) to the terminal cyanoacrylic acids ef fi-ciently. Nevertheless, in S3 and S4 dyes, the HOMO levels were entirely populated on DTP moiety and LUMOs on the cyanoacrylic acid anchoring units as well as on the donating moieties. Hence, the encumbrances in the electronic transitions between the vibrational energy levels had been anticipated in S3 and S4 dyes.Table 1
Electro-optical parameters of dyes (S1eS4)
Dye lmax/nm (3104, M1cm1)a lmaxon TiO2(nm)b lem(nm)a Egopt(eV)c HOMO/LUMO (eV)d Stokes Shift (nm)e
S1 473 (9.20) 441 568 2.23 5.58/3.35 95
S2 484 (11.19) 457 610 2.14 5.47/3.33 126
S3 557 (7.46) 508 637 1.92 5.32/3.40 80
S4 395 (2.74), 564(7.90) 510 718 1.80 5.14/3.34 154
aAbsorption and PL emission wavelength measured in THF solution (105M). b Absorption spectra of the dyes on 1.5mm TiO
2film.
c Optical band gap calculated from absorption onset (Egopt¼1240/l edge). d HOMO¼[(E
onset0.45)4.8] eV where 0.45 V is the value for ferrocene versus Ag/Agþand 4.8 eV is the energy level of ferrocene below the vacuum, and LUMO of the dyes
calculated by subtraction of the optical band gap from the HOMO.
eStokes shift has been calculated from the difference betweenl
maxandlem.
Fig. 3. (a) Absorption spectra of dyes adsorbed on 1.5mm TiO2film, (b) Theoretical
2.3. Photovoltaic properties of DSSCs
The photovoltaic properties of DSSCs containing S1eS4 dyes were measured under simulated AM 1.5 irradiation condition (100 mW/cm2), where TiO2photoelectrodes with approximately
a thickness of 18
m
m and a working area of 0.25 cm2were utilized. The incident photon-to-current conversion efficiency (IPCE) and photocurrentevoltage (JeV) curves of DSSCs based on S1eS4 and N719 dyes are shown inFigs. 5 and 6, respectively, and the details of photovoltaic parameters, such as the open-circuit photovoltage (VOC), short-circuit photocurrent density (JSC),fill factor (FF), andsolar-to-electrical energy conversion efficiency (
h
) are listed in Table 2. Thefluorene-based S2 exhibited the best energy conver-sion efficiencies (h
¼4.73%) among S1eS4 dyes, with VOC¼0.61 V,JSC¼12.27 mA/cm2, and FF¼0.63 (seeTable 2). As described
pre-viously, due to the largest molar extinction coefficient, S2 dye had the highest light harvesting efficiency and consequently promoted S2 to have the best photovoltaic performance among all dyes (S1eS4). As shown inFig. 5, the IPCE spectra of S2 showed a broader response in the range of 300e700 nm and the maximum value exhibited a strikingly high plateau at 76%. Owing to the presence of highly conjugated electron-donating DTP moieties in S3 and S4 dyes, they showed broader (extended up to 800 nm) but much smaller maximum values of IPCE spectra than thefluorine-based S1 and S2 dyes. The decreased IPCE values suggest that there are poor injections of electrons from excited dyes to the TiO2conduction
bands. In contrast to S1 dye, the IPCE values of S2 were enhanced by the longer conjugated thiophene linkers. On the contrary, com-pared with S3 dye, S4 possessed much smaller IPCE values is at-tributed to the highest HOMO level of S4 dye (seeTable 1), which led to a slower regeneration of the oxidized dye and higher re-combination of photoinjected electrons.33 Furthermore, the in-crease of S4 dye aggregations on TiO2surface decreased the IPCE
values significantly (seeFig. 5) though it has the highest absorption wavelength.37The higher molar extinction coefficient and oscillator strength of S2 than S1 reflected to an enhanced light harvesting in S2 dye, and accordingly an improved JSC(12.27 mA/cm2) value was
observed. Conversely, compared with S3 dye, there were dramatic falls in both JSCand VOCvalues of S4 (though the molar extinction
coefficient and oscillator strength of S4 were higher than those of S3). As a consequence, higher aggregations of S4 than S3 on TiO2
surfaces caused the barrier in efficient electron injections from the excited dye to the conduction band of TiO2and comparably the
shorter lifetime of oxidized S4 dye caused a fast charge re-combination process at the titinia/dye/electrolyte interface of S4 dye.32Despite of both lower molar extinction coefficient and IPCE values of S3 (in contrast to S1), it showed a higher
h
value, which could be attributed to the red shift of the maximum absorption wavelength (l
max), the wider absorption spectra, and partlyas-cribed to the broadening of IPCE spectra towards a longer wave-length region.
Fig. 4. Cyclic voltammograms of dyes in deoxygenated THF containing 0.1 M TBAPF6at
room temperature. All potentials are in volts versus Ag/AgNO3at a scan rate of 100 mV/s.
Fig. 5. IPCE plots for the DSSCs based on the organic dyes (S1eS4 and N719).
Fig. 6. JeV curves of DSSCs based on the organic dyes (S1eS4 and N719) under illu-mination of simulated solar light (AM 1.5, 100 mW/cm2). The electrode used was 0.5 M
lithium iodide (LiI), 0.05 M iodine (I2), and 0.5 M 4-tert-butylpyridine (TBP) dissolved
in acetonitrile.
Table 2
Detailed photovoltaic parameters of organic dyes (S1eS4) measured at an irradiance of 100 mW/cm2AM 1.5 G sunlight Cell VOC(V) JSC(mA/cm2) FF h(%) sR(ms)a S1 0.59 9.83 0.61 3.52 0.66 S2 0.61 12.27 0.63 4.73 0.43 S3 0.58 9.80 0.65 3.70 0.46 S4 0.50 3.83 0.65 1.24 0.26 N719 0.72 15.12 0.66 7.19 1.60 as
In order to investigate the extent of charge recombination be-tween the oxidized dye and the redox couple, the recombination lifetime of photoinjected electrons with oxidized dyes was mea-sured by transient photovoltage at open circuit with the presence of LiI (0.5 M) in acetonitrile. The average electron lifetime was esti-mated approximately byfitting a decay of the open circuit voltage transient with exp(t/
s
R), where t is time ands
Ris an average timeconstant before recombination. As shown inFig. 7and listed the fitting data inTable 2, the higher HOMO level of S4 leads to a slower regeneration of the oxidized sensitizer with Iand thus a faster recombination of photoinjected electrons.40Therefore, the photo-current of S4 is the lowest value among other dyes. The strong and bathochromic absorption of S2 when compared with S1 resulted in the high monochromic quantum efficiency and photocurrent. The longer electron lifetime of S1 caused the higher monochromic quantum efficiency in the range of 350e550 nm than S3. Thus, the similar photocurrents of S1 and S3 were obtained.
To envisage the effects of co-adsorbent on the photovoltaic per-formance, S2 and S3 dyes were subjected to the studies of nano-crystalline TiO2-based DSSCs using 10 mM of CDCA as a co-adsorbent
during the sensitization processes. The IPCE and JeV curves of DSSCs bearing S2 and S3 dyes (with and without CDCA) are shown inFigs. 8a and b, respectively, and the detailed data are listed inTable 3. Re-gardless of the negligible improvement (2.1%) of efficiency in S2, the DSSC bearing S3 dye showed a significant improvement (16.5%) in its PCE value, where the co-adsorption of CDCA prevented the dye ag-gregation and resulted in a more efficient electron injection from the excited dye to the conduction band of TiO2, and thus to induce
a significant improvement in JSCvalue. Besides, there was
consider-able improvement in IPCE curve of S3 dye (seeFig. 8a), which agreed well with its JSCvalue (seeTable 3). However, almost no change in
h
value of S2 dye could be reasoned as the decrease of dye adsorption (without CDCA 2.91107, with CDCA 2.52107mol/cm2) due to the
use of CDCA23,38(seeTable S1of the Supplementary data) canceled with its enhanced electron injection from the excited dye to the conduction band of TiO2. In general, it can be concluded that the
applications of co-adsorbents enhance the electron injections from the oxidized dyes to the conduction bands of TiO2by suppressing the
aggregations; on the other hand, the co-adsorbents decrease the net light harvesting by reducing the net dye adsorptions on the TiO2
surfaces.
3. Conclusion
In summary, four novel AeDeA configured dyes (S1eS4) employing two different electron donating cores, such as the flu-orene (S1eS2) and DTP (S3eS4) units, and two symmetrical an-choring cyanoacrylic acid (acceptor) termini linked via various numbers of thiophene units were synthesized and studied for their applications in DSSCs. In this AeDeA configuration, S2 dye (con-taining electron donatingfluorene units) showed the highest molar extinction coefficient, as a result it produced the highest PCE value (
h
¼4.83%) with VOC¼0.61 V, JSC¼11.91 mA/cm2, and FF¼0.66 understandard AM 1.5 sunlight with a IPCE plateau of 76%. Besides, the
Fig. 7. Normalized electron lifetime of S1eS4 and N719 dye as a function of extracted charge under open circuit condition with the presence of LiI electrolyte (0.5 M) in acetonitrile solutions.
Fig. 8. (a) IPCE (b) JeV curves, of DSSCs based on S2eS3 dyes(with and without CDCA) under illumination of simulated solar light (AM 1.5, 100 mW/cm2). The electrode used
was 0.5 M lithium iodide (LiI), 0.05 M iodine (I2), and 0.5 M 4-tert-butylpyridine (TBP).
Table 3
Detailed photovoltaic parameters of organic dyes (S2 and S3) with and without addition of CDCA during the sensitization processa
Dye CDCA (mM) VOC(V) JSC(mA/cm2) FF h(%) Efficiency
improvement S2 0 0.61 12.27 0.63 4.73 2.1%
10 0.61 11.91 0.66 4.83 S3 0 0.58 9.80 0.65 3.70 16.5%
10 0.58 11.01 0.67 4.31
highly conjugated electron donating DTP moiety in S3eS4 for the molecular design of DSSC dyes wasfirst developed in this study. The symmetrical S3 dye (containing an electron donating DTP core) showed an effective
h
¼4.31%, with JSC¼11.01 mA/cm2, VOC¼0.58 V,and FF¼0.67. However, due to the high aggregation of dye mole-cules on TiO2surface and the short lifetime of the excited dyes, the
DTP-based S4 dye showed poor performance, which accelerated the charge recombination so as to decrease the photocurrent. 4. Experimental section
4.1. Materials
Chemicals and solvents were reagent grades and purchased from Aldrich, ACROS, TCI, Strem, Fluka, and Lancaster Chemical Co. THF (tetrahydrofuran) and DCM (dichloromethane) were distilled over sodium/benzophenone and calcium hydride, respectively, and freshly distilled before use. Tetra-n-butylammonium hexa-fluorophosphate (TBAPF6) was recrystallized twice from absolute
ethanol and further dried for two days under vacuum. N-Bromo-succinimide was recrystallized from distilled water and dried under vacuum. The other chemicals were used without further puri fica-tion. The synthetic routes and detailed procedures of S1eS4 dyes are shown inScheme 1. 3,30-Dibromo-2,20-bithiophene (4),362,20 -(9,9-dihexyl-9H- fluorene-2,7-diyl)bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolane) (9), and 7aec41were synthesized by the reported procedures. Intermediates 8aeb and 10aeb were synthesized by similar Suzuki coupling reaction and also S1eS4 were synthesized by alike Knoevenagel reaction, where two examples of the detailed synthetic procedures for 8a (Suzuki coupling reaction) and S1 (Knoevenagel reaction) are described. In addition, the synthetic procedures of the other intermediates will be described as well. The chemical structures for all products were confirmed by1H and13C
NMR spectroscopy, mass spectra (FAB), and elemental analyses. The
1H NMR spectra of intermediate compounds 6, 8a, 8b, 10a, and 10b
(Figs. S2eS6) and both1H and13C NMR spectra of S1eS4 dyes (Figs. S7eS14) are shown in the Supplementary data.
4.2. Synthesis
4.2.1. Heptadecane-9-ol (1). A solution of ethyl formate (10 g, 135 mmol) in dry THF (80 mL) was added dropwise to a fresh solution of octyl magnesium bromide, which was prepared from 1-bro-mooctane (58 g, 300 mmol) and magnesium (8.15 g, 340 mmol) in 150 mL dry THF. After then, the reaction mixture was stirred over-night at room temperature. Next, the reaction mixture was quenched by the addition of MeOH, followed by saturated aqueous NH4Cl. The
crude compound was extracted three times with ethyl acetate. The combined organic fractions were washed with brine and dried over MgSO4. After removal of the solvent, the residue was purified by
recrystalization from acetonitrile to afford heptadecane-9-ol (1) as white solids (30.91 g, 89.3%).1H NMR (300 MHz, CDCl
3),
d
(ppm): 3.58(m, 1H), 1.43e1.25 (m, 29H), 0.88 (t, J¼6.6 Hz, 6H).
4.2.2. 2-(Heptadecan-9-yl)isoindoline-1,3-dione (2). A solution of 1 (10 g, 39 mmol), triphenylphosphine (10.22 g, 39 mmol), and phthalimide (5.74 g, 39 mmol) in dry diethyl ether (60 mL) was purged with N2, and a solution of DIAD (7.70 mL, 39 mmol) in dry
diethyl ether (30 mL) was added slowly. After stirring overnight, the precipitate wasfiltered off, and then washed thoroughly with diethyl ether. After removal of the solvent by rotary evaporator, the crude product was purified by column chromatography (silica) using hexane/dichloromethane (9:1) as an eluent to give a viscous and colorless oil (10.85 g, 72.2%). 1H NMR (300 MHz, CDCl3),
d
(ppm): 7.82 (dd, J¼3.3, 5.7 Hz, 2H), 7.70 (dd, J¼3.0, 5.4 Hz, 2H), 4.21e4.14 (m, 1H), 2.10e1.99 (m, 2H), 1.78e1.64 (m, 2H), 1.25e1.26 (m, 24H), 0.84 (t, J¼6.3 Hz, 6H).4.2.3. Heptadecan-9-amine (3). A solution of 2 (15 g, 38.90 mmol) in absolute ethanol (200 mL) was purged with N2, and then hy-drazine monohydrate (5.55 mL, 116.7 mmol) was added. The mix-ture was heated to reflux overnight (about 12 h). Subsequently, 12 mL of HCl solution (5 M) was added, and the mixture was refluxed for an additional 15 min and then cooled. The precipitate wasfiltered off and washed with water. Ethanol was removed from thefiltrate by rotary evaporator, and NaOH solution (2 M) was added to make the solution alkaline (pH¼10e11). The crude com-pound was extracted three times with ethyl acetate. The combined organic layers were washed with brine and dried over MgSO4, and the solvents were removed by rotary evaporator to get a colorless oil (6.07 g, 61.1%).1H NMR (300 MHz, CDCl
3),
d
(ppm): 2.66 (m, 1H),1.38e1.26 (m, 30H), 0.87 (t, J¼6.3 Hz, 6H).
4.2.4. 4-(Heptadecan-9-yl)-4H-dithieno[3,2-b:20,30-d]pyrrole (5). Compound 4 (3 g, 9.3 mmol), t-BuONa (2.22 g, 23.10 mmol), Pd2dba3(0.212 g, 0.231 mmol), and BINAP (0.575 g, 0.924 mmol)
were dissolved in dry toluene (20 mL). The solution was purged with N2for 30 min. Heptadecan-9-amine (3) (2.84 g, 11.09 mmol)
was added via a syringe and the mixture was stirred at 110C under N2 atmosphere for 12 h. After cooling, water was added and extracted twice with diethyl ether. The combined organic layers were dried over MgSO4, and the solvents were removed by rotary evaporator. The crude product was purified by column chroma-tography (silica) using hexane as an eluent to give a white solid (3.1 g, 80.30%).1H NMR (300 MHz, CDCl3),
d
(ppm): 7.10 (d, J¼5.1 Hz,2H), 7.01 (d, J¼5.1 Hz, 2H), 4.24e4.18 (m, 1H), 2.06e1.97 (m, 2H), 1.87e1.78 (m, 2H), 1.61 (m, 24H), 0.85 (t, J¼6.9 Hz, 6H).
4.2.5. 4-(Heptadecan-9-yl)-2,6-bis(4,4,5,5-tetramethyl-1,3,2-dioxa-borolan-2-yl)-4H-dithieno[3,2-b:20,30-d]pyrrole (6). Compound 5 (1 g, 2.4 mmol) was dissolved in 50 mL of dry THF and the solution was cooled down to78C under nitrogen protection, then 2.4 mL
of n-BuLi (2.5 M in Hexane, 5.98 mmol) was added. The solution was warmed up to room temperature for 30 min and cooled again
Scheme 1. Synthetic Routes of Dyes (S1eS4). (i) THF (ii) PPh3, DIAD, Et2O, room
temperature (rt). (iii) (1) Hydrazine monohydrate, absolute ethanol, reflux; (2) 5.0 M HCl, reflux. (iv) Pd2dba3, BINAP, NaOtBu, toluene, 110C. (v) (1) n-BuLi, THF,78C to
rt; (2) 2-Isopropoxy-4,4,5,5-tetramethyl-[1,3,2] dioxaborolane,78C to rt. (vi) Pd
(PPh3)4, K2CO3, toluene/EtOH (3:1), 90 C. (vii) CNCH2COOH, NH4OAc, CH3COOH,
to78C. 2-Isopropoxy-4,4,5,5-tetramethyl-[1,3,2] dioxaborolane
(1.37 mL, 6.7 mmol) was rapidly injected into the solution by a sy-ringe, and the resulting mixture was stirred at78C for 1 h, and
followed by reacting overnight at room temperature. The resulting mixture was quenched with H2O and extracted with
dichloro-methane. The dichloromethane extracts were washed with satu-rated brine and dried with MgSO4. The solvent was removed by
rotary evaporator and the product was further purified by column chromatography (silica) using a mixture of hexane and dichloro-methane (4:1) as an eluent to yield a white solid (0.72 g, 45%). Mp: 147e149 C. 1H NMR (300 MHz, CDCl3),
d
(ppm): 7.50 (s, 2H),4.25e4.16(m, 1H), 2.08e1.86 (m, 2H), 1.86e1.76 (m, 2H), 1.37 (s, 24H), 1.14 (m, 24H), 0.84 (t, J¼6.9 Hz, 6H).13C NMR (75 MHz, CDCl
3),
d
(ppm): 147.8, 126.0, 120.7, 121.5, 84.3, 60.3, 35.2, 31.7, 31.5, 26.6, 25.0, 22.6, 14.2. MS (FAB): m/z [Mþ] 670; calcd m/z [Mþ] 669.42. 4.2.6. 5,50-(4-(Heptadecan-9-yl)-4H-dithieno[3,2-b:20,30 -d]pyrrole-2,6-diyl) dithiophene-2-carbaldehyde (8a). Mixture of compounds 6 (0.3 g, 0.46 mmol), 7a (0.197 g, 1.03 mmol), and K2CO3 (0.161 g,1.16 mmol) were dissolved in 20 mL of toluene/ethanol (3:1) and degassed for 10 min, which was followed by the addition of 20 mg Pd (PPh3)4as a catalyst. The resulting mixture was stirred under reflux
for 36 h. The solvent was removed under vacuum and extracted with dichloromethane and washed with water followed by a little brine. The organic phase was dried with anhydrous MgSO4, and the solvent
was removed by rotary evaporator. Afterward, the crude compound was purified by column chromatography (silica) using a mixture of hexane and dichloromethane (1:1) as an eluent. The obtained product was recrystallized from ethanol to yield an orange color solid (210 mg, 70%). Mp: 128e130C.1H NMR (300 MHz, DMSO-d6),
d
(ppm): 9.85 (s,2H), 7.96 (d, J¼3.9 Hz, 2H), 7.91 (s, 2H), 7.53 (d, J¼3.9 Hz, 2H), 4.49e4.44 (m, 1H), 2.06e2.03 (m, 2H), 1.83e1.79 (m, 2H), 1.06 (m, 24H), 0.71 (t, J¼6.9 Hz, 6H).13C NMR (75 MHz, DMSO-d
6),
d
(ppm):182.5, 148.2, 146.6, 142.1, 134.5, 133.9,124.9, 59.6, 34.4, 31.7, 29.3, 29.0, 26.4, 22.6, 14.4. MS (FAB): m/z [Mþ] 638; calcd m/z [Mþ] 637.22. 4.2.7. 50,500-(4-(Heptadecan-9-yl)-4H-dithieno[3,2-b:20,30 -d]pyrrole-2,6-diyl)di-20,200-bithiophene-5-carbaldehyde (8b). Compound 8b was synthesized by the same procedure as compound 8a, afforded an orange solid in 69.5% yield. Mp: 135e137C.1H NMR (300 MHz, DMSO-d6),
d
(ppm): 9.86 (s, 2H), 7.98 (d, J¼3.9 Hz, 2H), 7.70 (s, 2H), 7.55 (d, J¼3.9 Hz, 2H), 7.51 (d, J¼3.9 Hz, 2H), 7.35 (d, J¼3.9 Hz, 2H), 4.44 (m, 1H), 2.03 (m, 2H), 1.80 (m, 2H), 1.13e0.95 (m, 24H), 0.72 (t, J¼6.9 Hz, 6H).13C NMR (75 MHz, DMSO-d 6),d
(ppm): 182.7, 146.6, 146.0, 142.1, 140.0, 134.2, 133.3, 128.7, 125.1, 59.8, 34.4, 31.8, 29.4, 29.2, 26.4, 22.6, 14.4. MS (FAB): m/z [Mþ] 802; calcd m/z [Mþ] 801.19. 4.2.8. 50,500-(9,9-Dihexyl-9H-fluorene-2,7-diyl)di-2,20-bithiophene-50-carbaldehyde (10a). Compound 10a was synthesized by the same procedure as compound 8a, afforded a yellow solid in 78.2% yield. Mp: 143e145C.1H NMR (300 MHz, CDCl3),
d
(ppm): 9.89 (s, 2H), 7.73e7.69 (m, 4H), 7.62 (dd, J¼1.5, 7.8 Hz, 2H), 7.56 (s, 2H), 7.39e7.35 (m, 4H), 7.30 (d, J¼3.9 Hz, 2H), 2.07e2.01(m, 4H),1.14e1.06 (m,12H), 0.75 (t, J¼6.6 Hz, 6H), 0.69 (m, 4H).13C NMR (75 MHz, CDCl 3),d
(ppm): 182.6, 152.21, 147.4, 147.0, 141.76, 140.0, 137.6, 135.1, 132.8, 127.4, 125.2, 124.3, 124.2, 120.7, 120.2, 55.6, 40.6, 31.7, 29.85, 23.0, 22.8, 14.2. MS (FAB): m/z [Mþ] 719; calcd m/z [Mþ] 718.21.4.2.9. 50,500-(9,9-Dihexyl-9H-fluorene-2,7-diyl)-di-2,20:50,200
-terthio-phene-500-carbaldehyde (10b). Compound 10b was synthesized by the same procedure as compound 8a, afforded a reddish yellow solid in 75.0% yield. Mp: 184e186C.1H NMR (300 MHz, CDCl3),
d
(ppm): 9.87 (s, 2H), 7.71e7.68 (m, 4H), 7.60 (dd, J¼1.8, 8.1 Hz, 2H), 7.56 (s, 2H), 7.33 (d, J¼3.9 Hz, 2H), 7.31 (d, J¼3.9 Hz, 2H) 7.26e7.23 (m, 4H), 7.18 (d, J¼3.9 Hz, 2H), 2.06e2.01(m, 4H), 1.15e1.07 (m, 12H), 0.76 (t, J¼6.6 Hz, 6H), 0.69 (m, 4H).13C NMR (75 MHz, CDCl 3),d
(ppm): 182.6, 152.1, 147.0, 145.2, 141.8, 140.7, 139.5, 137.6, 135.6, 134.6, 132.9, 127.3, 125.7, 125.0, 124.7, 124.2, 124.0, 120.5, 120.0, 55.6, 40.6, 31.68, 29.9, 23.0, 22.8, 14.2. MS (FAB): m/z [Mþ] 883; calcd m/z [Mþ] 882.18. 4.2.10. (2E,20E)-3,30-(50,500-(9,9-Dihexyl-9H-fluorene-2,7-diyl)bis (2,20-bithiophene-50,5-diyl))bis(2-cyanoacrylic acid) (S1). Acetic acid (40 mL) was added to aflask containing a mixture of compound 10a (400 mg, 0.56 mmol), ammonium acetate (170 mg, 2.25 mmol), and cyanoacetic acid (236 mg, 2.35 mmol). The mixture was refluxed for 36 h and allowed to cool to room temperature. The resulting solid wasfiltered and washed with excess of distilled water, followed by dichloromethane to give a dark brown solid (390 mg, 82.4%). Mp: 287e289C.1H NMR (300 MHz, DMSO-d6),d
(ppm): 8.49 (s, 2H), 7.98 (d, J¼4.5 Hz, 2H), 7.87e7.81 (m, 4H), 7.70 (dd, J¼3.3 Hz, J¼9.9 Hz, 6H), 7.62 (d, J¼3.9 Hz, 2H), 2.06 (m, 4H), 1.03e0.96 (m, 12H), 0.66 (t, J¼6.3 Hz, 6H), 0.51 (m, 4H).13C NMR (75 MHz, DMSO-d6),d
(ppm): 164.3, 152.3, 147.0, 146.6, 146.3, 142.3, 141.0, 134.6, 132.6, 129.1, 126.2, 125.6, 125.4, 121.5, 120.4, 117.3, 98.7, 55.8, 31.5, 29.5, 24.1, 22.6, 14.5. MS (FAB): m/z [Mþ] 853; calcd m/z [Mþ] 852.22. Anal. Calcd for C49H44N2O4S4: C, 68.98; H, 5.20; N, 3.28.Found: C, 68.62; H, 5.49; N, 3.26.
4.2.11. 50,500-(9,9-Dihexyl-9H-fluorene-2,7-diyl)-di-[2,20:50,200
-ter-thiophene-500-(2-cyanoacrylic acid)] (S2). Compound S2 dye was
synthesized by the same procedure as S1, afforded dark brown solid in 82.0% yield. Mp: 302e304 C.1H NMR (300 MHz, DMSO-d6),
d
(ppm): 8.47 (s, 2H), 7.97 (d, J¼4.2 Hz, 2H), 7.83e7.76 (m, 4H), 7.63e7.58 (m, 8H), 7.49 (d, J¼3.6 Hz, 2H), 7.42 (d, J¼3.9 Hz, 2H), 2.06 (m, 4H), 1.00e0.95 (m, 12H), 0.65 (t, J¼6.3 Hz, 6H), 0.53 (m, 4H).13C NMR (75 MHz, DMSO-d6),d
(ppm): 164.3, 152.2, 146.9, 145.8, 144.6, 142.1, 140.7, 139.0, 135.1, 134.7, 134.2, 132.8, 128.8, 127.1, 126.1, 125.1, 125.0,121.3,120.1,117.2, 98.1, 55.1, 31.0, 29.1, 24.1, 22.1,14.4. MS (FAB): m/z [Mþ] 1017; calcd m/z [Mþ] 1016.19. Anal. Calcd for C57H48N2O4S6:C, 67.29; H, 4.76; N, 2.75. Found: C, 66.61; H, 5.02; N, 2.85.
4.2.12. (2E,20E)-3,30-(5,50 -(4-(Heptadecan-9-yl)-4H-dithieno[3,2-b:20,30-d]pyrrole-2,6-diyl)bis(thiophene-5,2-diyl))bis(2-cyanoacrylic acid) (S3). Compound S3 dye was synthesized by the same pro-cedure as S1, afforded dark brown solid in 89.6% yield. Mp: 281e283C.1H NMR (300 MHz, DMSO-d6),
d
(ppm): 8.44 (s, 2H), 7.94 (d, J¼4.5 Hz, 2H), 7.90 (s, 2H), 7.58 (d, J¼3.9 Hz, 2H), 4.49 (m, 1H), 2.07e2.03 (m, 2H), 1.78e1.74 (m, 2H), 1.04 (m, 24H) 0.71 (t, J¼6.9 Hz, 6H).13C NMR (75 MHz, DMSO-d 6),d
(ppm) 164.5, 148.4, 146.8, 142.3, 134.6, 134.1, 125.0, 117.4, 116.7, 112.4, 97.9, 59.8, 34.5, 31.9, 29.4, 29.2, 26.5, 22.7, 14.5. MS (FAB): m/z [Mþ] 772; calcd m/z [Mþ] 771.23. Anal. Calcd for C41H45N3O4S4: C, 63.78; H, 5.87; N,5.44. Found: C, 63.34; H, 5.80; N, 5.30.
4.2.13. (2E,20E)-3,30-(50,500 -(4-(Heptadecan-9-yl)-4H-dithieno[3,2-b:20,30-d]pyrrole-2,6-diyl)bis(20,200-bithiophene-50,50 -diyl))bis(2-cya-noacrylic acid) (S4). Compound S4 dye was synthesized by the same procedure as S1, afforded dark brown solid in 88.2% yield. Mp: 292e294C.1H NMR (300 MHz, DMSO-d6),
d
(ppm): 8.42 (s, 2H), 7.92 (d, J¼4.2 Hz, 2H), 7.68 (s, 2H), 7.51e7.46 (m, 4H), 7.29 (d, J¼3.6 Hz, 2H), 4.39 (m, 1H), 2.01 (m, 2H), 1.75 (m, 2H), 1.11e0.91 (m, 24H) 0.70 (t, J¼6.6 Hz, 6H).13C NMR (75 MHz, DMSO-d 6),d
(ppm): 164.3, 146.8, 146.1, 142.3, 140.9, 134.4, 134.2, 133.4, 128.8, 125.3, 117.3, 110.8, 98.5, 59.9, 34.6, 31.9, 29.5, 29.2, 26.5, 22.7, 14.5. MS (FAB): m/z [Mþ] 935; calcd m/z [Mþ] 935.20. Anal. Calcd for C49H49N3O4S6: C,62.85; H, 5.27; N, 4.49. Found: C, 62.62; H, 5.58; N, 4.78. 4.3. Measurement and characterizations
1H NMR spectra were recorded on a Varian unity 300 MHz
spectrometer using DMSO-d6 and CHCl3-d as solvents. Elemental
analyzer. UVevis absorption spectra were recorded in dilute THF solutions (105 M) on an HP G1103A spectrophotometer, and photoluminescence (PL) spectra were obtained on a Hitachi F-4500 spectrophotometer. Cyclic voltammetry (CV) measurements were performed using a BAS 100 electrochemical analyzer with a stan-dard three-electrode electrochemical cell in a 0.1 M tetrabuty-lammonium hexafluorophosphate (TBAPF6) solution (in THF) at
room temperature with a scanning rate of 100 mV/s. During the CV measurements, the solutions were purged with nitrogen for 30 s. In each case, a carbon coating rod as the working electrode, a plati-num wire as the counter electrode, and a silver wire as the quasi-reference electrode were used, and Ag/AgCl (3 M KCl) electrode was served as the reference electrode for all potentials quoted herein. The redox couple of ferrocene/ferrocenium ion (Fc/Fcþ) was used as an external standard. The corresponding HOMO and LUMO levels were calculated from the onset oxidation potential (Eox/onset) and
UVevis absorption edge (Egopt), respectively.
4.3.1. TiO2paste preparation. The preparation of TiO2precursor and
the electrode fabrication were carried out based on previous re-port.42with an autoclaved temperature of 240C. The precursor solution was made according to the following procedure: 430 mL of 0.1 M nitric acid solution under vigorous stirring was slowly com-bined with 72 mL Ti(C3H7O)4to form a mixture. After the
hydro-lysis, the mixture was heated at 85C in a water bath and stirred vigorously for 8 h in order to achieve the peptization. When the mixture was cooled down to room temperature, the resultant col-loid wasfiltered, and the filtrate was then heated in an autoclave at a temperature of 240C for 12 h to grow the TiO2particles. When
the colloid was cooled to room temperature, it was ultrasonically vibrated for 10 min. The TiO2colloid was concentrated to 13 wt %,
followed by the addition of 30 wt % (with respect to TiO2weight) of
poly (ethylene glycol) (PEG, MW¼20,000 g/mol) to prevent the film from cracking while drying.
4.3.2. Device fabrication. The TiO2paste was then deposited on an
FTO glass substrate by the glass rod method with a dimension of 0.50.5 cm2. The polyester tape (3 M) was used as an adhesive on
two edges of an FTO glass. The tape was removed after the TiO2
paste was spread on the FTO by a glass rod and the TiO2paste was
dried in the air at room temperature for 1 h. The TiO2-coated FTO
was heated to 500C at a heating rate of 10C/min and maintained for 30 min before cooled to room temperature. After repeating the same procedure described above to control the thickness of a TiO2
film, the final coating was carried out with TiO2pastes containing
different sizes (300 nm and 20 nm with weight percentages of 30 and 70, respectively) of light scattering TiO2 particles and then
heated to 500C. The thicknesses of TiO2films were measured by
a profilometer (Dektak3, Veeco/Sloan Instruments, Inc.). The adsorbed density of each dye was calculated from the concentra-tion difference of each soluconcentra-tion before and after TiO2film
immer-sion. The TiO2 electrode with a geometric area of 0.25 cm2 was
immersed in a acetonitrile/tert-butanol mixture (volume ratio 1:1) containing 3104 M cis-di(thiocyanato)bis(2,20-bipyridyl-4,40
-dicarboxylato) ruthenium(II) bis(tetrabutylammonium) (N719, Solaronix SA) or in the THF solutions containing 3104M organic sensitizers for overnight. A thermally platinized FTO was used as a counter electrode and was controlled to have an active area of 0.36 cm2by adhered polyester tape with a thickness of 60
m
m. After rinsing with CH3CN or THF, the photoanode was placed on top ofthe counter electrode and tightly clipping them together to form a cell. Electrolyte was then injected into the space and then sealing the cell with the Torr Seal cement (Varian, Inc.). The electrolyte was composed of 0.5 M lithium iodide (LiI), 0.05 M iodine (I2), and 0.5 M
4-tert-butylpyridine (TBP) dissolved in acetonitrile. The photo-voltage transients of assembled devices were recorded with
a digital oscilloscope (LeCroy, WaveSurfer 24Xs). Pulsed laser ex-citation was applied by a Q-switched Nd:YAG laser (Continuum, model Minilite II) with 1 Hz repetition rate at 532 nm and a 5 ns pulse width at half-height. The beam size was slightly larger than 0.50.5 cm2to cover the area of the device. The photovoltage of
each device was adjusted by incident pulse energy to be 40 mV. 4.3.3. Device measurements. A 0.60.6 cm2 cardboard mask was
clipped onto the device to constrain the illumination area. The photoelectrochemical characterizations on the solar cells were carried out by using an Oriel Class A solar simulator (Oriel 91195A, Newport Corp.). Photocurrentevoltage characteristics of the DSSCs were recorded with a potentiostat/galvanostat (CHI650B, CH In-struments, Inc.) at a light intensity of 1.0 sun calibrated by an Oriel reference solar cell (Oriel 91150, Newport Corp.). The mono-chromatic quantum efficiency was recorded through a mono-chromator (Oriel 74100, Newport Corp.) at short circuit condition. The intensity of each wavelength was in the range of 1e3 mW/cm2. The photovoltage transients of assembled devices were recorded with a digital oscilloscope (LeCroy, WaveSurfer 24Xs). Pulsed laser excitation was applied by a Q-switched Nd:YAG laser (Continuum, model Minilite II) with 1 Hz repetition rate at 532 nm and a 5 ns pulse width at half-height. The beam size was slightly larger than 0.50.5 cm2to cover the area of the device. The photovoltage of
each device was adjusted by incident pulse energy to be 50 mV. The average electron lifetime can be estimated approximately byfitting a decay of the open circuit voltage transient with exp(t/
s
R), wheret is time and
s
Ris an average time constant before recombination.4.3.4. Quantum chemistry computation. The predicted structures of the molecules were optimized by using B3LYP hybrid functional, and 6-31G*basis sets. For each of the molecules, a number of conformational isomers were examined and the one with the lowest energy was used. For the excited states, we have employed the time-dependent density functional theory (TD-DFT) with the B3LYP functional. The lowest 33 singletesinglet excited states were calculated using TDDFT (up to an energy of ca. 250 nm). All of the analyses were performed under Gaussian 03 (G03) (revision E.01) program package43by using density functional theory (DFT). The simulated spectra with the oscillator strength (f) values were obtained with the program GaussSum 2.1.2.
Acknowledgements
We are grateful to the National Center for High-performance computing for computer time and facilities. Thefinancial supports of this project provided by the National Science Council of Taiwan (ROC) through NSC 97-2113-M-009-006-MY2, National Chiao Tung University through 97W807, and Energy and Environmental Lab-oratories (charged by Dr. Chang-Chung Yang) in Industrial Tech-nology Research Institute (ITRI) are acknowledged.
Supplementary data
Supplementary data associated with this article can be found in online version atdoi:10.1016/j.tet.2010.11.044. These data include MOL files and InChIKeys of the most important compounds de-scribed in this article.
References and notes
1. (a) Gaudiana, R. J. Phys. Chem. Lett. 2010, 1, 1288; (b) Hagfeldt, A.; Gr€atzel, M. Chem. Rev. 1995, 95, 49.
2. O’Regan, B.; Gr€atzel, M. Nature 1991, 353, 737. 3. Gr€atzel, M. Nature 2001, 414, 338.
4. (a) Nazeeruddin, M. K.; Kay, A.; Rodicio, I.; Humpbry-Baker, R.; Miiller, E.; Liska, P.; Vlachopoulos, N.; Gr€atzel, M. J. Am. Chem. Soc. 1993, 115, 6382; (b)
Staniszewski, A.; Ardo, S.; Sun, Y.; Castellano, E. N.; Meyer, G. J. J. Am. Chem. Soc. 2008, 130, 11586; (c) Sauvage, F.; Fischer, M. K. R.; Mishra, A.; Zakeeruddin, S. M.; Nazeeruddin, M. K.; B€auerle, P.; Gr€atzel, M. ChemSusChem 2009, 2, 761. 5. (a) Nazeeruddin, M. K.; Zakeeruddin, S. M.; Humphry-Baker, R.; Jirousek, M.;
Liska, P.; Vlachopoulos, N.; Shklover, V.; Fischer, C.-H.; Gr€atzel, M. Inorg. Chem. 1999, 38, 6298; (b) Schmidt-Mende, L.; Kroeze, J. E.; Durrant, J. R.; Nazeeruddin, M. K.; Gr€atzel, M. Nano Lett. 2005, 5, 1315.
6. Chen, C.-Y.; Chen, J.-G.; Wu, S.-J.; Li, J.-Y.; Wu, C.-G.; Ho, K.-C. Angew. Chem., Int. Ed. 2008, 47, 7342.
7. Abbotto, A.; Barolo, C.; Bellotto, L.; De Angelis, F.; Gr€atzel, M.; Manfredi, N.; Marinzi, C.; Fantacci, S.; Yum, J.-H.; Nazeeruddin, M. K. Chem. Commun. 2008, 5318. 8. Yin, J.-F.; Chen, J.-G.; Lu, Z.-Z.; Ho, K.-C.; Lin, H.-C.; Lu, K.-L. Chem. Mater. 2010,
22, 4392.
9. Yin, J.-F.; Bhattacharya, D.; Hsu, Y.-C.; Tsai, C.-C.; Lu, K.-L.; Lin, H.-C.; Chen, J.-G.; Ho, K.-C. J. Mater. Chem. 2009, 19, 7036.
10. (a) Wang, Z.-S.; Cui, Y.; Dan-oh, Y.; Kasada, C.; Shinpo, A.; Hara, K. J. Phys. Chem. C 2007, 111, 7224; (b) Hara, K.; Sayama, K.; Ohga, Y.; Shinpo, A.; Suga, S.; Arakawa, H. Chem. Commun. 2001, 569; (c) Hara, K.; Kurashige, M.; Danoh, Y.; Kasada, C.; Shinpo, A.; Suga, S.; Sayama, K.; Arakawa, H. New J. Chem. 2003, 27, 783. 11. Tanaka, H.; Takeichi, A.; Higuchi, K.; Motohiro, T.; Takata, M.; Hirota, N.;
Na-kajima, J.; Toyoda, T. Sol. Energy Mater. Sol. Cells 2009, 93, 1143.
12. Ito, S.; Zakeeruddin, S. M.; Humphry-Baker, R.; Liska, P.; Charvet, R.; Comte, P.; Nazeeruddin, M. K.; Pechy, P.; Takata, M.; Miura, H.; Uchida, S.; Gr€atzel, M. Adv. Mater. 2006, 18, 1202.
13. Tang, J.; Wu, W.; Hua, J.; Li, J.; Li, X.; Tian, H. Energy Environ. Sci. 2009, 2, 982. 14. Guo, M.; Diao, P.; Ren, Y.-J.; Meng, F.; Tian, H.; Cai, S.-M. Sol. Energy Mater. Sol.
Cells 2005, 88, 23.
15. Sayama, K.; Tsukagoshi, S.; Mori, T.; Hara, K.; Ohga, Y.; Shinpou, A.; Abe, Y.; Suga, S.; Arakawa, H. Sol. Energy Mater. Sol. Cells 2003, 80, 47.
16. Shibano, Y.; Umeyama, T.; Matano, Y.; Imahori, H. Org. Lett. 2007, 9, 1971. 17. (a) Won, Y. S.; Yang, Y. S.; Kim, J. H.; Ryu, J.-H.; Kim, K. K.; Park, S. S. Energy Fuels
2010, 24, 3676; (b) Tan, S.; Zhai, J.; Fang, H.; Jiu, T.; Ge, J.; Li, Y.; Jiang, L.; Zhu, D. Chem.dEur. J. 2005, 11, 6272.
18. Thomas, K. R. J.; Lin, J. T.; Hsu, Y.-C.; Ho, K.-C. Chem. Commun. 2005, 4098. 19. (a) Chen, C.-H.; Hsu, Y.-C.; Chou, H.-H.; Thomas, K. R. J.; Lin, J. T.; Hsu, C.-P.
Chem.dEur. J. 2010, 16, 3184; (b) Baheti, A.; Tyagi, P.; Thomas, K. R. J.; Hsu, Y.-C.; Lin, J. T. J. Phys. Chem. C 2009, 113, 8541.
20. (a) Kim, S.; Choi, H.; Kim, D.; Song, K.; Kang, S. O.; Ko, J. Tetrahedron 2007, 63, 9206; (b) Choi, H.; Lee, J. K.; Song, K.; Kang, S. O.; Ko, J. Tetrahedron 2007, 63, 3115. 21. (a) Mishra, A.; Fischer, M. K. R.; B€auerle, P. Angew. Chem., Int. Ed. 2009, 48, 2474;
(b) Li, Y.-T.; Chen, C.-L.; Hsu, Y.-Y.; Hsu, H.-C.; Chi, Y.; Chen, B.-S.; Liu, W.-H.; Lai, C.-H.; Lin, T.-Y.; Chou, P.-T. Tetrahedron 2010, 66, 4223; (c) Zhang, L.; Liu, Y.; Wang, Z.; Liang, M.; Sun, Z.; Xue, S. Tetrahedron 2010, 66, 3318; (d) Hwang, S.; Lee, J. H.; Park, C.; Lee, H.; Kim, C.; Park, C.; Lee, M.-H.; Lee, W.; Park, J.; Kim, K.; Park, N.-G.; Kim, C. Chem. Commun. 2007, 4887.
22. (a) Chen, H.; Huang, H.; Huang, X.; Clifford, J. N.; Forneli, A.; Palomares, E.; Zheng, X.; Zheng, L.; Wang, X.; Shen, P.; Zhao, B.; Tan, S. J. Phys. Chem. C 2010, 114, 3280; (b) Kim, D.; Kang, M. S.; Song, K.; Kang, S. O.; Ko, J. Tetrahedron 2008, 63, 10417. 23. Qu, S.; Wu, W.; Hua, J.; Kong, C.; Long, Y.; Tian, H. J. Phys. Chem. C 2010, 114,
1343.
24. (a) Im, H.; Kim, S.; Park, C.; Jang, S.-H.; Kim, C.-J.; Kim, K.; Park, N.-G.; Kim, C. Chem. Commun. 2010, 46, 1335; (b) Burke, A.; Schmidt-Mende, L.; Ito, S.; Gr€atzel, M. Chem. Commun. 2007, 234; (c) Snaith, H. J. Adv. Funct. Mater. 2010, 20, 13; (d) Velusamy, M.; Thomas, K. R. J.; Lin, J. T.; Hsu, Y.-C.; Ho, K. C. Org. Lett. 2005, 7, 1899.
25. Park, S. S.; Won, Y. S.; Choi, Y. C.; Kim, J. H. Energy & Fuels 2009, 23, 3732. 26. Abbotto, A.; Manfredi, N.; Marinzi, C.; De Angelis, F.; Mosconi, E.; Yum, J.-H.;
Xianxi, Z.; Nazeeruddin, M. K.; Gr€atzel, M. Energy Environ. Sci. 2009, 2, 1094. 27. Heredia, D.; Natera, J.; Gervaldo, M.; Otero, L.; Fungo, F.; Lin, C.-Y.; Wong, K.-T.
Org. Lett. 2010, 12, 12.
28. Ogawa, K.; Rasmussen, S. C. J. Org. Chem. 2003, 68, 2921.
29. Mishara, S. P.; Palai, A. K.; Srivastava, R.; Kamalasanan, M. N.; Patri, M. J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 6514.
30. (a) Zhou, E.; Nakamura, M.; Nishizawa, T.; Zhang, Y.; Wei, Q.; Tajima, K.; Yang, C.; Hashimoto, K. Macromolecules 2008, 41, 8302; (b) Yue, W.; Zhao, Y.; Shao, S.; Tian, H.; Xie, Z.; Geng, Y.; Wang, F. J. Mater. Chem. 2009, 19, 2199; (c) Zhou, E.; Yamakawa, S.; Tajima, K.; Yang, C.; Hashimoto, K. Chem. Mater. 2009, 21, 4055. 31. Liu, J.; Zhang, R.; Sauve, G.; Kowalewski, T.; McCullough, R. D. J. Am. Chem. Soc.
2008, 130, 13167.
32. Sanchez-Diaz, A.; Martinez-Ferrero, E.; Palomares, E. J. Mater. Chem. 2009, 19, 5381.
33. Gonc¸alves, A. S.; Davolos, M. R.; Masaki, N.; Yanagida, S.; Mori, S.; Nogueira, A. F. J. Appl. Phys. 2009, 106, 064316.
34. Kopidakis, N.; Benkstein, K. D.; de Lagemaat, J. V.; Frank, A. J. J. Phys. Chem. B 2003, 107, 11307.
35. Yang, H.-Y.; Yen, Y.-S.; Hsu, Y.-C.; Chou, H.-H.; Lin, J. T. Org. Lett. 2010, 12, 16. 36. Wei, Y.; Yang, Y.; Yeh, J.-M. Chem. Mater. 1996, 8, 2659.
37. (a) Chen, K.-F.; Hsu, Y.-C.; Wu, Q.; Yeh, M.-C. P.; Sun, S.-S. Org. Lett. 2009, 11, 377; (b) Li, G.; Jiang, K. J.; Bao, P.; Li, Y.-F.; Li, S.-L.; Yang, L.-M. New J. Chem. 2009, 33, 868.
38. Fischer, M. K. R.; Wenger, S.; Wang, M.; Mishra, A.; Zakeeruddin, S. M.; Gr€atzel, M.; B€auerle, P. Chem. Mater. 2010, 22, 1836.
39. Cao, Y.; Bai, Y.; Yu, Q.; Cheng, Y.; Liu, S.; Shi, D.; Gao, F.; Wang, P. J. Phys. Chem. C 2009, 113, 6290.
40. O’Regan, B. C.; Durrant, J. R. J. Phys. Chem. B 2006, 110, 8544.
41. Zhu, Y.; Rabindranath, A. R.; Beyerlein, T.; Tieke, B. macromolecules 2007, 40, 6981.
42. Huang, C. Y.; Hsu, Y.-C.; Chen, J.-G.; Suryanarayanan, V.; Lee, K. M.; Ho, K.-C. Sol. Energy Mater. Sol. Cells 2006, 90, 2391.
