Hexaethylsubporphyrins: β-alkyl analogues in the subporphyrin family

Abstract

Two new subporphyrins were synthesized for the first time from a β-substituted pyrrole i.e. 3,4-diethylpyrrole via pyridine-tri-N-(3,4-diethylpyrrolyl)borane as building blocks. These β-hexaethylsubporphyrins are true contracted congeners of β-octaethylporphyrin (OEP). While the meso-triphenyl derivative of hexaethylsubporphyrin could be synthesized by following the reported method, the meso-free analogue could only be synthesized by condensation with trioxane, in the presence of catalytic methanesulfonic acid. These contracted macrocycles display interesting absorption, and emission behaviour including substituent dependent S2 fluorescence owing to the presence of flexible electron donating ethyl groups at their β-positions. The optical response and ultrafast S2 state dynamics of these systems suggest that it may be possible to tune the properties of the subporphyrin to develop efficient systems for solar energy capture and conversion processes.

BIII 5‐Arylsubporphyrins and BIII Subporphine

“…We also attempted to use 1,3,5-trioxane as aC 1-source, because it was successfully applied in the synthesis of b-haxaethyl B III subporphyrin. [16] This attempt did not work in the presentr eaction. The 1 HNMR spectrum of 4 showedo nly three singlet signals (d = 8.92, 8.11, and 0.63 ppm for the meso, b,a xial-OMe protons, respectively), reflecting the remarkably simple structure with C 3v symmetry.I nt he 11 The normalized UV/Vis absorption spectra of 1-4 are shown in Figure 3a.I nterestingly,t he peak top of Soret-like band is progressively blue-shifted in the order of 1 (373 nm), 2 (362 nm), 3 (352 nm), and 4 (341 nm), clearly indicating the electronic interaction of the meso-phenyl group with the B III subporphyrin core.…”

“…178 °C) was found to be ineffective. We also attempted to use 1,3,5‐trioxane as a C1‐source, because it was successfully applied in the synthesis of β‐haxaethyl B III subporphyrin . This attempt did not work in the present reaction.…”

meso‐Free BIII Subporphyrins with Electron‐donating Groups

“…Since the first report in 2006, [1] B III subporphyrins have emerged as important ring-contracted porphyrinoids with attractive attributes such as 14π-electronic aromatic characters, bowlshaped curved structures, and variable electronic properties depending upon the peripheral substituents. [2,3] Recent progress in the chemistry of B III subporphyrins has achieved the synthesis of various B III subporphyrins including meso-aryl-substituted, [4] meso-alkyl-substituted, [5] β-alkyl-substituted, [6] pyrrole-reduced, [7] pyrrole-modified, [8] and meso-unsubstituted [9] derivatives. Among these, B III 5,10-diphenylsubporphyrin 1 a was synthesized in 2012 [9a] (Figure 1) and has been used for preparations of a wide range of meso-substituted subporphyrins.…”

meso‐Functionalization of Boron(III) Subporphyrin with Boron(III) meso‐Lithiosubporphyrin

“…Since the first report in 2006, B III subporphyrins have emerged as a new class of ring‐contracted porphyrinoids with attractive attributes such as 14 π‐electronic aromatic character, bowl‐shaped curved structures, and variable electronic properties depending upon the peripheral substituents . Recent progress in the chemistry of B III subporphyrins has enabled the synthesis of various B III subporphyrins including meso ‐aryl‐substituted, meso ‐alkyl‐substituted, β‐alkyl‐substituted, meso ‐unsubstituted, pyrrole‐reduced, and pyrrole‐modified derivatives. However, it is still desirable to develop new methods for the effective functionalization of B III subporphyrins.…”