A Comprehensive Study on Tetraaryltetrabenzoporphyrins

Abstract

Tetraaryltetrabenzoporphyrins (TATBPs) show, due to their optoelectronic properties, rising potential as dyes in various fields of physical and biomedical sciences. However, unlike in the case of porphyrins, the potential structural diversity of TATBPs has been explored only to little extent, owed mainly to synthetic hurdles. Herein, we prepared a comprehensive library of 30 TATBPs and investigated their fundamental properties. We elucidated structural properties by X‐ray crystallography and found explanations for physical properties such as solubility. Fundamental electronic aspects were studied by optical spectroscopy as well as by electrochemistry and brought in context to the stability of the molecules. Finally, we were able to develop a universal synthetic protocol, utilizing a readily established isoindole synthon, which gives TATBPs in high yields, regardless of the nature of the used arylaldehyde and without meticulous chromatographic purifications steps. This work serves as point of orientation for scientists, that aim to utilize these molecules in materials, nanotechnological, and biomedical applications.

Synthesis and Photophysical Properties of Hexabenzocoronene‐Tetrabenzoporphyrin Architectures

“…We started our investigation by the preparation of meso ‐tetrakis‐HBC‐tetrabenzoporphyrin ( meso ‐HBC‐TBP) 4 and tetrakis‐ N ‐HBC‐phthalimidoporphyrin 7 (Scheme 1) via the retro‐Diels‐Alder approach. By utilizing our previously described reaction conditions, [ 22 ] condensation of 4,7‐dihydro‐4,7‐ethano‐2 H ‐isoindole 1 and formylated hexaarylbenzene HAB‐CHO [ 15d ] provided tetraaryltetrabenzoporphyrins (TATBP) 3 in 62 % yield. After Scholl oxidation of 3 , using iron(III) chloride in nitromethane or DDQ and triflic acid, target 4 was obtained in 90 % yield.…”

“…The electronic properties of the tetrapyrroles were investigated by steady‐state absorption and emission spectroscopy (Figure 4a and b) and compared with the data of T t Bu PTBP , which was described previously. [ 22 ] The absorption spectrum of T t Bu PTBP exhibits typical bathochromic shifted absorption features of nonplanar saddle‐shaped TATBPs: a Soret band at 464 nm, four Q‐bands at 547, 588, 637 and 696 nm and a shoulder at 626 nm. The replacement of the 4‐ tert‐ butylphenyl substituents of T t Bu PTBP with HAB moieties (compound 3 ) results in a bathochromic shift of the Soret band by 12 nm and around 8 nm for the Q‐bands (Figure 3a).…”

“…Upon excitation of the Soret band, all porphyrins within this work exhibit three emission maxima with the typical fine structure that was found earlier for TATBPs (Figure 4c and d). [ 22 ] Regarding the fluorescence spectra of 3 and T t Bu PTBP , the locations of the emission bands are red‐shifted by around 12 nm. In contrast to 3 , the emission bands of 4 are hypsochromic shifted by around 6 nm compared to reference TATBP T t Bu PTBP .…”

“…[ 31 ] As it can be seen in Figure 6a, both conjugates show the typical saddle‐shape distortion that can be found for TATBPs. [ 22 ] While the HBCs in meso ‐conjugate 4 are sterically confined by the surrounding benzo moieties, which leads to an averaged dihedral angle between the HBC and the porphyrin plane of 76°, the HBCs at the periphery of the imido‐conjugate 7 are sterically unhindered. Yet, the energetically most favored dihedral angle for 7 is found around 30°.…”

“…4,7‐Dihydro‐4,7‐ethano‐2 H ‐isoindole 1 , [ 22 ] 1‐(4‐formylphenyl)‐2,3,4,5,6‐pentakis‐(4‐ tert ‐butylphenyl)benzene HAB‐CHO [ 15d ] and 1‐(4‐aminophenyl)‐2,3,4,5,6‐pentakis‐(4‐ tert ‐butylphenyl)benzene HAB‐NH 2 [ 23 ] were prepared according to literature. A modified synthetic protocol towards 4,7‐dihydro‐5,6‐dimethoxycarbonyl‐4,7‐ethano‐2 H ‐isoindole 2 is given in the Supporting Information.…”