Femtosecond Transient Absorption studies

The transient absorption spectra of Sm-BF2 and Sm-B(OR)2 dyes on TiO2 with excitation at 640 nm and monitored at 4800 nm are displayed in Figure 4-10. Since the transient absorption signal of electrons on TiO² conduction band is at ~4.8 μm, the transient absorption signal at 4800 nm directly displays the kinetics of the electron injection on TiO2. As the excitation photon excites the smaragdyrin molecules to the first singlet excited state, the excited electron inject into the conduction band of TiO2, and the absorption signal at 4.8 μm shows the rising behavior. The rising lifetime of all the smaragdyrin dyes demonstrates same electron injection lifetime around 50 femtosecond (fs). However, the transient absorption spectrum of N719 on TiO2 shows the double injection processes, the first at 50 fs and the second around 500 ps. The two injection processes for N719 could be attributed to the injection from the singlet and triplet excited states. Compared with N719, the excited oxasmaragdyrins only inject electron from the S1 state of the dye to TiO2 CB. Although the energy gap between the LUMO and TiO2

conduction band edge is the smallest for Sm-BF2, the electron injection kinetics for oxasmaragdyrins on TiO2 does not affect by the energy gap due to the highly conjugated linker.

In addition, the transient absorption spectra also show the back electron transfer from TiO2 to the dye cation.

0 5 10 100 1000

Figure 4-10. The transient absorption spectra of Sm-BR2 dyes.

The length of alkoxy chain on boron atom in the oxasmaragdyrin is systemically increased from B(OEt)2 to B(ODec)2, but it has negligible impact on the back electron transfer rate.

Although the electron withdrawing strength of fluoride atoms is stronger than that of alkoxy groups, the back electron transient rate is not influenced by it.Based on the femtosecond transient absorption spectra of oxasmaragdyrins, the rates of electron injection and back electron transfer of oxasmaragdyrins with excitation at the S1 state are almost the same. They are mainly caused by the electronic densities at LUMO and LUMO+1 of oxasmaragdyrins molecules.

4.3 Conclusions

In conclusion, we are able to demonstrate for the first time that boron complexes of oxasmaragdyrin, a class of core-modified expanded porphyrin, can be applied as efficient photosensitizers for DSSC. Five novel oxasmaragdyrin boron complexes were prepared in four steps with 18% overall yield. Without exhausted coupling reactions to add electron donating groups, the plain oxasmaragdyrin boron chelated complex has already reached 5.7% power conversion efficiency. We demonstrated that the HOMO and LUMO energy levels of these dyes match quite well with the redox potential of I^-/I3- electrolyte and with the TiO2 conducting band. Boron chelated oxasmaragdyrins provide desired redox potentials, high absorption coefficients, high stability, and higher power conversion efficiencies suitable for an effective sensitizer in DSSCs. More importantly, broad absorption spreading the entire visible region

and its lower energy Q band covering part of the NIR region make this class of compounds an optimistic candidate for being one of the future selections of porphyrin-sensitized solar cells.

By appending alkoxy substituents with different lengths, we are able to show that the alkyl chains extended from the central core can shield the molecules from aggregation while maintaining high degree of dye loading. Our current charge extraction measurements revealed faster charge recombination in comparison with the highest efficiency porphyrin dyes and provided an important direction to further improve the power conversion efficiency of these oxasmaragdyrin based expanded porphyrin dyes. We hope that this pioneer work can provide new insights and can inspire broad explorations on using diverse expanded porphyrins as NIR dyes for DSSC or on developing new suitable assemblies to take full advantage of expanded porphyrins to absorb NIR/IR light.

4.4 Experimental Section

4.4.1 General Techniques and Materials

All chemicals were obtained from commercial sources and used as received without further purification. All the reactions were carried out under nitrogen atmosphere. Solvents used in reactions were dried by PureSolv MD 5 system (Innovative Technology, Inc). Flash chromatography was carried out by using basic alumina (63-200 μm, Merck) and silica gel (40-63 μm, Merck). Analytical TLC was performed on Merck silica gel plates. ¹H, ¹³C, ¹¹B and ¹⁹F NMR spectra were recorded on a Bruker Avance 400 FT and DRX 500 spectrometer. NMR samples were prepared in CDCl3 and THF as d-solvents and chemical shifts were reported in δ scale. The standard abbreviations s, d, t, q, m and bs refer to singlet, doublet, triplet, quartet, multiplet and broad singlet respectively. Coupling constant (J) values are reported in Hertz.

The ESI ion trap mass spectra were measured by a Finnigan MAT LCQ mass spectrometer.

The HR-FAB spectra were conducted on a JMS-700 double focusing mass spectrometer.

Transmittance and reflection UV‒visible absorption spectra of the oxasmaragdyrins in THF and adsorbed on TiO² electrodes, respectively, were recorded on a JASCO V-670 UV-vis/NIR spectrophotometer. Steady-state fluorescence spectra were acquired by using a Varian Cary Eclipse fluorescence spectrophotometer. The cyclic voltammetry measurements of all oxasmaragdyrins were carried out on CHI 621B electrochemical analyzer (CH Instruments, Austin, TX, USA) in degassed THF containing 0.1 M tetrabutylammonium hexafluorophosphate (Bu⁴NPF⁶) as the supporting electrolyte. The cell assembly consists of a glossy carbon as the working electrode, a silver wire as the pseudo-reference electrode, and a platinum wire as the auxiliary electrode. The scan rate for all measurements was fixed at 50 mV/sec. A ferrocene^+1/0 redox couple was used as the internal standard and the potential values obtained in reference to the silver electrode were converted to the vacuum scale. The density functional theory (DFT) and time-dependent density functional (TD-DFT) calculations were performed with Gaussian 09 package to study the electron distribution of the frontier molecular orbitals and the photoexcitation transitions. All ground state geometries of oxasmaragdyrins Sm-BR2 were optimized in the gas phase by the hybrid B3LYP functional and the 6-31G basis set, and the TD-DFT calculation were based on the same functional and basis set.^[14] The molecular orbitals were visualized by the Chemoffice software.

4.4.2 Synthesis

5(p-Methoxycarbonylphenyl)dipyrromethane (7)

A mixture of methyl-4-formylbenzoate (3.28 g, 0.02 mol) and pyrrole (137 ml, 2 mol) was degassed with N2 for 15 min. at room temperature. TFA (150 μl, 0.002 mol) was then added and the mixture was stirred at room temperature for 3 hrs. After completion of the reaction, NaOH (2.4 g, 0.06 mol) was added and mixture was stirred for 1 h and then filtered. The filtrate was concentrated and pyrrole was removed under vacuum. The crude obtained after removing pyrrole was subjected to silica gel column chromatography using DCM/hexanes (4:6, Rf = 0.2) as eluting solvent to obtain the dipyrromethane (4.8 g, 86% Yield). ¹H NMR (400 MHz, CDCl3) δ: 3.91 (s, 3H, CH³), 5.53 (s, 1H, meso CH), 5.89 (s, 2H, β-pyrrole), 6.16 (m, 2H, β-pyrrole), 6.72 (m, 2H, α-pyrrole), 7.28 (m, 2H, Ph), 7.98, (m, 4H, Ph, NH) ppm; ¹³C NMR (100 MHz, CDCl3) δ: 43.97, 52.08, 107.50, 108.57, 117.54, 128.41, 129.91, 131.58, 147.34 ppm.

2,5-Bis(p-tolylmethanol)furan (8)

Furan (1 ml, 13.75 mmol) was added to a solution of n-BuLi (22 ml, 34.37 mmol) and TMEDA (5.15 ml, 34.37 mmol) in 40 ml dry hexane under N2. The reaction mixture was heated at reflux temperature for 1 h and then cooled to 0 ^oC. To this suspension, a pre-cooled solution of p-tolualdehyde (3.48 ml, 29.5 mmol) in 40 ml dry THF was added drop wise. After the addition was complete, the mixture was warmed to room temperature while stirring for 30 minutes.

Saturated NH4Cl solution was added to quench the reaction. The organic phase was extracted with H2O, brine and then dried over MgSO4. The crude product was subjected to silica gel column chromatography using EA/hexanes (3:7, Rf = 0.2) as eluting solvent to get furan diol (2.47 g, 58% Yield). ¹H NMR (400 MHz, CDCl³) δ: 2.36 (s, 6H, Me), 2.42 (bs, 2H, OH), 5.75 (d, 2H, meso CH), 5.96 (d, β-furan), 7.16 (d, 4H, Ar), 7.30 (d, 4H, Ar) ppm; ¹³C NMR (100 MHz, CDCl3) δ: 21.15, 69.99, 108.04, 108.11, 126.61, 129.12, 137.83, 156.20 ppm.

5,10-Ditolyl-16-oxatripyrrane (9)

Furan-diol (8) (1 g, 3.25 mmol) was dissolved in pyrrole (8.9 ml, 130 mmol) under N2. To this solution BF3•OEt2 (0.41 ml, 3.25 mmol) was added. The mixture was stirred for 30 min. at room temperature. After completion of reaction as confirmed by TLC, the reaction was quenched by adding aqueous NaOH (0.1 N, 50 ml). The mixture was extracted with DCM and washed with water. The organic layer was dried over MgSO⁴ and excess pyrrole was removed under vacuum. The crude oil was purified by column chromatography on silica using DCM/Hexanes (1:1, Rf = 0.4) as eluting solvent to get pure oxatripyrrane (800 mg, 60% Yield).

1H NMR (400 MHz, CDCl3) δ: 2.37 (s, 6H, Me), 5.39 (s, 2H, meso CH), 5.94 (s, 2H, β-pyrrole),

5.98 (d, 2H, β-furan), 6.16 (m, 2H, β-pyrrole), 6.65 (s, 2H, α-pyrrole), 7.13 (m, 8H, Ar), 7.98 (bs, 2H, NH) ppm; ¹³C NMR (100 MHz, CDCl3): δ= 21.01, 43.83, 107.01, 107.76, 108.11, 117.12, 128.17, 129.16, 131.21, 136.57, 137.74, 155.03 ppm.

19-(4-Methoxycarbonylphenyl)-5,10-di(p-tolyl)-25-oxasmaragdyrin (10)

5(p-methoxycarbonylphenyl)dipyrromethane (7) (513 mg, 1.26 mmol) and 5,10-ditolyl-16-oxatripyrrane (10) (354 mg, 1.26 mmol) were dissolved in 750 ml of DCM and stirred under nitrogen for 5 min. The reaction was initiated by adding TFA (10 µl, 0.126 mmol) and the stirring was continued for 90 min. DDQ (860 mg, 3.79 mmol) was then added and the reaction mixture was stirred in open air for additional 90 min. The solvent was removed and crude compound was purified by basic alumina column chromatography eluted with DCM/hexanes (3:7, Rf = 0.35) to get the desired oxasmaragdyrin as a green solid (325 mg, 38% yield). ¹H NMR (400 MHz, CDCl3) δ: 2.72 (s, 6H; CH3), 4.12 (s, 3H; OCH3), 7.62 (d, 4H, J = 7.76 Hz;

Ph), 8.10 (d, 4H, J = 7.8 Hz; Ph), 8.49 (m, 6H; Ph and β-pyrrole), 8.83 (s, 2H; β-furan), 8.95 (d, 2H, J = 4.32 Hz, β-pyrrole), 9.43 (d, 2H, J = 4.28 Hz; β-pyrrole), 9.52 (d, 2H, J = 4.28 Hz;

β-pyrrole) ppm; HRMS-FAB+: m/z calcd for C⁴⁵H³⁵N⁴O³: 679.2709, found 679.2708 [M+H]⁺. BF2-[19-(4-Methoxycarbonylphenyl)-5,10-di(p-tolyl)-25-oxasmaragdyrin] (11)

Oxasmaragdyrin (9) (700 mg, 1.03 mmol) was dissolved in DCM (100 ml) and triethylamine (5.72 ml, 41.2 mmol) was added at room temperature. After 10 min BF³•OEt² (6.53 ml, 51.5 mmol) was added and the stirring was continued for 30 min. Completion of the reaction was confirmed by TLC. The reaction mixture was washed thoroughly with 0.1 M NaOH solution and water. The combined organic layers were dried over MgSO4, filtered and the solvent was removed under reduced pressure. The crude compound was purified by silica gel column chromatography, using DCM/hexanes (3:7, R^f = 0.27) to afford the desired compound (11) as green solid (464 mg, 62% yield). ¹H NMR (400 MHz, CDCl3) δ: ‒3.97 (t, 2H; NH), 2.8 (s, 6H;

Tol), 4.13 (s, 3H; OCH3), 7.71 (d, 4H, J = 7.76 Hz; Ph), 8.31 (d, 4H, J = 7.8 Hz; Ph), 8.64 (d, 2H, J = 8.28 Hz; Ph), 8.71 (d, 2H, J = 8.28 Hz; Ph), 9.04 (dd, 2H, ¹J = 4.34, ²J = 1.68; β-pyrrole), 9.52 (s, 2H; β-furan), 9.58 (d, 2H, J = 4.52 Hz, β-β-pyrrole), 10.24 (dd, 2H, ¹J = 4.36,

2J = 1.84; β-pyrrole), 10.34 (d, 2H, J = 4.48 Hz; β-pyrrole) ppm; ¹¹B NMR (160.4 MHz, CDCl3) δ: ‒12.79 (br s) ppm; ¹⁹F NMR (470.5 MHz, CDCl3) δ: ‒149.22 (br s) ppm; ¹³C NMR (100 MHz, CDCl3) δ: 167.45, 149.87, 144.02, 139.50, 137.95, 134.82, 134.28, 131.41, 130.68, 130.44, 129.56, 129.47, 128.30, 125.03, 123.90, 123.78, 122.14, 120.96, 120.43, 117.08, 107.10, 52.46, 21.64 ppm; HRMS-FAB+: m/z calcd for C⁴⁵H³³BF²N⁴O³: 726.2614, found 726.2617 [M]⁺.

B(OC2H5)2-[19-(4-Methoxycarbonylphenyl)-5,10-di(p-tolyl)-25-oxasmaragdyrin] (12b) BF2-Oxasmaragdyrin (11) (218 mg, 0.3 mmol) was dissolved in dry DCM (100 ml) in the presence of aluminum chloride (240 mg, 1.8 mmol) under nitrogen. The resulting mixture was refluxed for 10 min and then ethanol (10 ml) was added. The reaction mixture was stirred for additional 10 min at the same temperature. The reaction mixture was concentrated and purified by column chromatography on silica gel using hexanes/dichloromethane (1:1, Rf = 0.4) to get the desired product (12b) as green solid (210 mg, 90% yield). ¹H NMR (400 MHz, CDCl³) δ:

‒3.91 (t, 6H, J = 7.36 Hz; CH³), ‒3.59 (q, 4H, J = 7.16 Hz; OCH²), ‒1.17 (s, 2H; NH), 2.78 (s, 6H; Tol), 4.16 (s, 3H; OCH3), 7.67 (d, 4H, J = 7.64 Hz; Ph), 8.31 (d, 4H, J = 7.56 Hz; Ph), 8.63 (d, 2H, J = 7.72 Hz; Ph), 8.72 (d, 2H, J = 8.32 Hz; Ph), 8.78 (dd, 2H, ¹J = 3.26, ²J = 2.24; β-pyrrole), 9.39 (s, 2H; β-furan), 9.44 (d, 2H, J = 3.92 Hz, β-β-pyrrole), 9.98 (dd, 2H, ¹J = 3.54, ²J

= 2.04; β-pyrrole), 10.17 (d, 2H, J = 4.48 Hz; β-pyrrole) ppm; ¹¹B NMR (160.4 MHz, CDCl³) δ: ‒12.67 (br s); ¹³C NMR (125 MHz, CDCl3) δ: 167.58, 149.51, 144.65, 140.1, 137.42, 134.94, 134.34, 132.25, 131.64, 130.05, 129.26, 128.97, 128.05, 124.62, 124.31, 122.97, 121.36, 119.38, 118.85, 117.17, 106.64, 52.48, 48.68, 21.63, 11.45 ppm; HRMS-FAB+: m/z calcd for C49H43BN4O5 : 778.3327, found 778.3333 [M]⁺.

B(OC4H9)2-[19-(4-Methoxycarbonylphenyl)-5,10-di(p-tolyl)-25-oxasmaragdyrin] (12c) BF2-Oxasmaragdyrin (11) (218 mg, 0.3 mmol) was dissolved in dry DCM (100 ml) in the presence of aluminum chloride (240 mg, 1.8 mmol) under nitrogen. The resulting mixture was refluxed for 10 min and then 1-butanol (10 ml) was added. The reaction mixture was stirred for additional 10 min. The reaction mixture was concentrated and purified by column chromatography on silica gel using hexanes/DCM (6:4, Rf = 0.4) to get the desired product (12c) as green solid (221 mg, 88% yield). ¹H NMR (400 MHz, CDCl3) δ: ‒3.73 (m, 4H; OCH2),

‒3.53 (m, 8H; CH2), ‒1.79 (m, 6H; CH3), ‒1.26 (s, 2H; NH), 2.78 (s, 6H; Tol), 4.16 (s, 3H;

OCH³), 7.67 (d, 4H, J = 7.72 Hz; Ph), 8.28 (d, 4H, J = 7.76 Hz; Ph), 8.62 (d, 2H, J = 8.16 Hz;

Ph), 8.71 (d, 2H, J = 8.16 Hz; Ph), 8.75 (dd, 2H, ¹J = 3.9, ²J = 1.96; pyrrole), 9.36 (s, 2H; β-furan), 9.44 (d, 2H, J = 4.36 Hz, β-pyrrole), 9.97 (dd, 2H, ¹J = 4.22, ²J = 1.6; β-pyrrole), 10.16 (d, 2H, J = 4.40 Hz; β-pyrrole) ppm; ¹¹B NMR (160.4 MHz, CDCl3) δ: ‒12.47 (br s) ppm; ¹³C NMR (125 MHz, CDCl³) δ: 167.53, 149.57, 144.77, 140.3, 137.46, 134.89, 134.31, 132.49, 131.75, 130.34, 129.22, 128.05, 124.52, 124.45, 122.9, 121.31, 119.36, 118.83, 117.24, 106.82, 52.53, 52.35, 30.84, 27.96, 21.59, 14.4, 10.62 ppm; HRMS-FAB+: m/z calcd for C53H51BN4O5: 834.3953, found 834.3957 [M]⁺.

B(OC7H15)2-[19-(4-Methoxycarbonylphenyl)-5,10-di(p-tolyl)-25-oxasmaragdyrin] (12d) BF2-Oxasmaragdyrin (11) (218 mg, 0.3 mmol) was dissolved in dry DCM (100 ml) in the presence of aluminum chloride (240 mg, 1.8 mmol) under nitrogen. The resulting mixture was refluxed for 10 min and then 1-heptanol (10 ml) was added. The reaction mixture was stirred for additional 10 min. The reaction mixture was concentrated and purified by column chromatography on silica gel using hexanes/DCM (6:4, Rf = 0.43) to get the desired product (12d) as green solid (228 mg, 83% yield). ¹H NMR (400 MHz, CDCl³) δ: ‒3.76 (m, 8H;

OCH²CH²), ‒3.44 (m, 4H; CH²), ‒1.56 (m, 4H; CH²), ‒1.27 (s, 2H; NH), ‒0.69 (m, 4H; CH²), 0.12 (m, 4H; CH2), 0.31 (t, 6H; CH3), 2.79 (s, 6H; Tol), 4.16 (s, 3H; OCH3), 7.67 (d, 4H, J = 7.72 Hz; Ph), 8.28 (d, 4H, J = 7.76 Hz; Ph), 8.62 (d, 2H, J = 8.16 Hz; Ph), 8.71 (d, 2H, J = 8.12 Hz; Ph), 8.76 (dd, 2H, ¹J = 4.22, ²J = 1.96; β-pyrrole), 9.37 (s, 2H; β-furan), 9.43 (d, 2H, J = 4.36 Hz, β-pyrrole), 9.96 (dd, 2H, ¹J = 4.2, ²J = 1.72; pyrrole), 10.16 (d, 2H, J = 4.40 Hz; β-pyrrole) ppm; ¹¹B NMR (160.4 MHz, CDCl3) δ: ‒12.52 (br s) ppm; ¹³C NMR (100 MHz, CDCl3) δ: 167.58, 149.56, 144.8, 140.33, 137.46, 134.94, 134.37, 132.48, 131.72, 130.31, 129.25, 129.17, 128.06, 125.51, 124.55, 124.46, 122.9, 121.33, 119.42, 118.81, 117.22, 106.78, 52.92, 52.4, 30.32, 30.17, 26.28, 26.05, 21.6, 21.47, 13.58 ppm; HRMS-ESI: m/z calcd for C⁵⁹H⁶³BN⁴O⁵ : 918.4892, found 918.4886 [M]⁺.

B(OC10H21)2-[19-(4-Methoxycarbonylphenyl)-5,10-di(p-tolyl)-25-oxasmaragdyrin] (12e) BF2-Oxasmaragdyrin (11) (165 mg, 0.23 mmol) was dissolved in dry DCM (100 ml) in the presence of aluminum chloride (181 mg, 1.36 mmol) under nitrogen. The resulting mixture was refluxed for 10 min and then 1-decanol (10 ml) was added. The reaction mixture was stirred for additional 10 min. The mixture was concentrated and purified by column chromatography on silica gel using hexanes/DCM (6:4, Rf = 0.48) to get the desired product (12e) as green solid (131 mg, 57% yield). ¹H NMR (400 MHz, CDCl3) δ: ‒3.75 (m, 8H;

OCH²CH²), ‒3.45 (m, 4H; CH²), ‒1.58 (m, 4H; CH²), ‒1.27 (s, 2H; NH), ‒0.69 (m, 4H; CH²), 0.14 (m, 4H; CH2), 0.66 (m, 4H; CH2), 0.78 (t, 6H; CH3), 0.89 ( m, 4H; CH2), 1.10 (m, 4H;

CH2), 2.79 (s, 6H; Tol), 4.16 (s, 3H; OCH3), 7.67 (d, 4H, J = 7.68 Hz; Ph), 8.28 (d, 4H, J = 7.84 Hz; Ph), 8.62 (d, 2H, J = 8.08 Hz; Ph), 8.71 (d, 2H, J = 8.08 Hz; Ph), 8.76 (dd, 2H, ¹J = 4.14, ²J = 1.84; β-pyrrole), 9.36 (s, 2H; β-furan), 9.43 (d, 2H, J = 4.4 Hz, β-pyrrole), 9.96 (dd, 2H, ¹J = 4.26, ²J = 1.84; β-pyrrole), 10.16 (d, 2H, J = 4.44 Hz; β-pyrrole) ppm; ¹¹B NMR (160.4 MHz, CDCl3) δ: ‒12.44 (br s) ppm; ¹³C NMR (125 MHz, CDCl3) δ: 167.57, 149.56, 144.81, 140.33, 137.46, 134.93, 134.39, 132.48, 131.73, 130.31, 129.24, 129.18, 128.05, 124.55, 124.47, 122.9, 121.33, 119.43, 118.81, 117.22, 106.79, 52.91, 52.39, 31.6, 30.88, 28.86, 28.68,

28.02, 26.66, 26.05, 22.55, 21.62, 14.01 ppm; HRMS-FAB+: m/z calcd for C65H75BN4O5: 1002.5831, found 1002.5847 [M]⁺.

BF2-[19-(4-Carboxyphenyl)-5,10-di(p-tolyl)-25-oxasmaragdyrin] (Sm-BF2)

Oxasmaragdyrin (11) (125 mg, 0.17 mmol) was dissolved in 20 ml THF. To this mixture, KOH (193 mg, 3.4 mol) dissolved in 2 ml water was added and refluxed for 12 h. After cooling, the solvent was removed under vacuum. To the crude product DCM was added and extracted with 1 N HCl. The organic layer was dried over MgSO4 and concentrated. Crude product was purified by silica gel column chromatography using DCM/MeOH (9.5:0.5, Rf = 0.1) as eluent to get the desired product Sm-BF2 as green solid (114 mg, 94% yield). ¹H NMR (400 MHz, THF-d8) δ: ‒3.88 (t, 2H; -NH), 2.78 (s, 6H; Tol), 7.73 (d, 4H, J = 7.64 Hz; Ph), 8.32 (d, 4H, J

= 7.68 Hz; Ph), 8.66 (d, 2H, J = 7.96 Hz; Ph), 8.75 (d, 2H, J = 7.96 Hz; Ph), 9.01 (d, 2H, J = 4.12; β-pyrrole), 9.55 (s, 2H; β-furan), 9.64 (d, 2H, J = 4.40 Hz, β-pyrrole), 10.42 (dd, 2H, ¹J

= 4.54, ²J =1.44; β-pyrrole), 10.51 (d, 2H, J = 4.44 Hz; β-pyrrole) ppm; ¹¹B NMR (160.4 MHz, THF-d8) δ: ‒14.76 (br s) ppm; ¹⁹F NMR (470.5 MHz, THF-d8) δ: ‒151.35 (br s) ppm; ¹³C NMR (125 MHz, THF-d8) δ: 168.00, 152.74, 150.74, 144.47, 140.64, 138.9, 138.19, 135.8, 135.18, 132.44, 131.67, 131.42, 130.6, 129.23, 128.85, 125.96, 125.69, 124.98, 124.86, 123.37, 121.72, 121.69, 118.44, 107.83, 21.75 ppm; HRMS-FAB+: m/z calcd for C44H31BF2N4O3: 712.2457, found 712.2449 [M]⁺.

B(OC2H5)2-[19-(4-Carboxyphenyl)-5,10-di(p-tolyl)-25-oxasmaragdyrin] [Sm-B(OEt)2] Oxasmaragdyrin 12b (40 mg, 0.052 mmol) was dissolved in 10 ml THF. To this mixture, KOH (56 mg, 1.04 mol) dissolved in 2 ml water was added and refluxed for 12h. After cooling, the solvent was removed under vacuum. Residue was dissolved in DCM and extracted with 1 N HCl. The organic layer was dried over MgSO⁴ and concentrated. Crude product was purified by silica gel column chromatography using DCM/MeOH (9.5:0.5, Rf = 0.16) as eluent to get the desired product Sm-B(OEt)2 as green solid (35 mg, 88% yield). ¹H NMR (400 MHz, CDCl3) δ: ‒3.92 (t, 6H, J = 6.88 Hz; CH3), ‒3.61 (q, 4H, J = 6.94 Hz; OCH2), ‒1.22 (s, 2H;

NH), 2.79 (s, 6H; Tol), 7.68 (d, 4H, J = 7. 64 Hz; Ph), 8.31 (d, 4H, J = 7.64 Hz; Ph), 8.76 (m, 6H; β-pyrrole, Ph), 9.39 (s, 2H; β-furan), 9.48 (d, 2H, J = 2.96 Hz; β-pyrrole), 10.00 (d, 2H, J

= 2.12 Hz; β-pyrrole), 10.2 (d, 2H, J = 4.28 Hz; β-pyrrole) ppm; ¹¹B NMR (160.4 MHz, CDCl3) δ: ‒12.64 (br s) ppm; ¹³C NMR (125 MHz, CDCl3) δ: 171.07, 149.7, 145.67, 140.28, 137.5, 135.1, 134.43, 132.43, 131.81, 130.27, 129.91, 128.09, 124.63, 122.96, 121.48, 119.51, 118.97, 117.03, 106.79, 48.75, 21.6, 11.43 ppm; HRMS- FAB+: m/z calcd for C⁴⁸H⁴¹BN⁴O⁵: 764.3170, found 764.3169 [M]⁺.

B(OC4H9)2-[19-(4-Carboxyphenyl)-5,10-di(p-tolyl)-25-oxasmaragdyrin] [Sm-B(OBu)2] Oxasmaragdyrin 12c (200 mg, 0.24 mmol) was dissolved in 50 ml THF. To this mixture, KOH (269 mg, 4.8 mol) dissolved in 5 ml water was added and refluxed for 12h. After cooling, the solvent was removed under vacuum. To the crude product DCM was added and extracted with 1 N HCl. The organic layer was dried over MgSO4 and concentrated. Crude product was purified by silica gel column chromatography using DCM/MeOH (9.5:0.5, Rf = 0.15) as eluent to get the desired product Sm-B(OBu)2 as green solid (169 mg, 86% yield). ¹H NMR (400 MHz,CDCl³) δ: ‒3.73 (t, 4H; OCH²), ‒3.51 (m, 8H; CH²), ‒1.8 (t, 6H; CH³), ‒1.29 (s, 2H;

NH), 2.8 (s, 6H; Tol), 7.69 (d, 4H, J = 7.5 Hz; Ph), 8.29 (d, 4H, J = 7.65 Hz; Ph), 8.78 (m, 6H;

β-pyrrole, Ph), 9.38 (s, 2H; β-furan), 9.5 (s, 2H, β-pyrrole), 10.01 (d, 2H, J = 3.16, β-pyrrole), 10.21 (d, 2H, J = 4.35 Hz; β-pyrrole) ppm; ¹¹B NMR (160.4 MHz, CDCl3) δ: ‒12.47 (br s) ppm; ¹³C NMR (125 MHz, CDCl³) δ: 171.71, 149.61, 145.76, 143.13, 140.32, 137.51, 135.13, 134.37, 132.51, 131.72, 130.39, 129.92, 128.09, 125.51, 124.51, 122.92, 121.46, 119.51, 118.96, 117.02, 106.9, 52.56, 30.33, 27.98, 21.64, 14.43, 10.67 ppm; HRMS-FAB+: m/z calcd for C52H49BN4O5 : 820.3796, found 820.3798 [M]⁺.

B(OC7H15)2-[19-(4-Carboxyphenyl)-5,10-di(p-tolyl)-25-oxasmaragdyrin] [Sm-B(OHep)2] Oxasmaragdyrin 12d (200 mg, 0.22 mmol) was dissolved in 50 ml THF. To this mixture, KOH (244 mg, 4.36 mmol) dissolved in 5 ml water was added and refluxed for 12h. After cooling, the solvent was removed under vacuum. To the crude product DCM was added and extrac ted with 1N HCl. The organic layer was dried over MgSO⁴ and concentrated. Crude product was purified by silica gel column chromatography using DCM/MeOH (9.5:0.5, Rf = 0.16) as eluent to get the desired product Sm-B(OHep)2 as green solid (188 mg, 94% yield). ¹H NMR (400 MHz, CDCl3) δ: ‒3.74 (m, 8H; OCH2CH2), ‒3.43 (m, 4H; CH2), ‒1.55 (m, 4H; CH2), ‒1.28 (s, 2H; NH), ‒0.67 (m, 4H; CH2), 0.14 (m, 4H; CH2), 0.32 (t, 6H; CH3), 2.79 (s, 6H; Tol), 7.69 (d, 4H, J = 7.76 Hz; Ph), 8.29 (d, 4H, J = 7.72 Hz; Ph), 8.79 (m, 6H; β-pyrrole, Ph), 9.39 (s, 2H;

β-furan), 9.49 (d, 2H, J = 4.36 Hz, β-pyrrole), 9.99 (dd, 2H, ¹J = 4.14, ²J = 1.6; β-pyrrole), 10.2 (d, 2H, J = 4.36 Hz; β-pyrrole) ppm; ¹¹B NMR (160.4 MHz, CDCl3) δ: ‒12.47 (br s) ppm; ¹³C NMR (100 MHz, CDCl3) δ: 171.49, 149.58, 145.71, 140.34, 137.48, 135.13, 134.39, 132.47, 131.69, 130.34, 129.9, 128.33, 128.08, 124.57, 124.52, 122.9, 121.45, 119.52, 118.9, 116.98, 106.83, 52.93, 30.19, 26.29, 26.05, 21.61, 21.48, 13.6 ppm; HRMS-ESI: m/z calcd for C58H61BN4O5: 904.4735, found 904.4739 [M]⁺.

B(OC10H21)2-[19-(4-Carboxyphenyl)-5,10-di(p-tolyl)-25-oxasmaragdyrin][Sm-B(ODec)2] Oxasmaragdyrin 12e (131 mg, 0.13 mmol) was dissolved in 30 ml THF. To this mixture, KOH (145 mg, 2.61 mmol) dissolved in 5 ml water was added and refluxed for 12h. After cooling, the solvent was removed under vacuum. To the crude product DCM was added and extracted with 1N HCl. The organic layer was dried over MgSO4 and concentrated. Crude product was purified by silica gel column chromatography using DCM/MeOH (9.5:0.5, Rf = 0.18) as eluent to get the desired product Sm-B(ODec)2 as green solid (112 mg, 91% yield). ¹H NMR (400 MHz, CDCl³) δ: ‒3.75 (m, 8H; OCH²CH²), ‒3.45 (m, 4H; CH²), ‒1.58 (m, 4H; CH²), ‒1.3 (s, 2H; NH), ‒0.68 (m, 4H; CH2), 0.15 (m, 4H; CH2), 0.67 (m, 4H; CH2), 0.79 (t, 6H; CH3), 0.88 ( m, 4H; CH2), 1.10 (m, 4H; CH2), 2.8 (s, 6H; Tol), 7.68 (d, 4H, J = 7.72 Hz; Ph), 8.29 (d, 4H, J = 7.68 Hz; Ph), 8.77 (m, 6H; β-pyrrole, Ph), 9.39 (s, 2H; β-furan), 9.49 (d, 2H, J = 4.08 Hz, β-pyrrole), 9.99 (d, 2H, J = 2.56; β-pyrrole), 10.19 (d, 2H, J = 3.92 Hz; β-pyrrole) ppm; ¹¹B NMR (160.4 MHz, CDCl3) δ: ‒12.46 (br s) ppm; ¹³C NMR (100 MHz, CDCl3) δ:

172.09, 149.57, 145.76, 140.34, 137.48, 135.15, 134.43, 132.47, 131.67, 130.33, 129.94, 128.07, 124.58, 124.53, 122.9, 121.46, 119.54, 118.91, 116.96, 106.84, 52.9, 31.63, 28.89, 28.71, 28.04, 26.67, 26.05, 22.58, 21.65, 21.57, 14.05 ppm; HRMS-FAB+: m/z calcd for C⁶⁴H⁷³BN⁴O⁵ : 988.5674, found 988.5676 [M]⁺.