Zinc‐ and Cadmium meso‐Aryl‐Isoporphyrins: Non‐Aromatic NIR Dyes with Distinct Conformational Features

Abstract

A series of pyrrolyl and dipyrrinyl isoporphyrins carrying different phenyl and thienyl groups is reported. The compounds are obtained by a one-pot approach in the presence of a template reagent. Thienyl derivatives gave better yields, and were the only subclass to form with steric hindrance. The structural analyses carried out on compounds 1 and 14 revealed distinct conformational differences which are likely to result from an intramolecular NH … Cl hydrogen bridge of the pyrrolyl subclass. In addition, this hydrogen bridge strongly favors one of the two possible atropisomers. Hindered rotation of the meso-aryl groups is observed only in the cases of methylbenzothienyl derivatives 10 and 15 and leads to the observation of several diastereomers. NIR absorptions up to 923 nm are found throughout. Electrochemical investigations into the 1e À and 2e À reduced species unravel axial ligand exchange dynamics for the zinc isoporphyrin radical, and the probable formation of a zinc phlorinate.

Pyrrolyl‐Appended Zinc Porphodimethenes: Branched Oligopyrrole Products From the Templated One‐Pot Isoporphyrin Synthesis

“…[11] A chromatographic enrichment and isolation of the putative tripyrrin complexes was carried out for benzaldehyde 4 and the similarly behaving 4-methoxybenzaldehyde. [7] In both cases deep blue solutions of 6 (C 6 H 5 ; 5.7 % yield) and 7 (4-MeOC 6 H 4 ; 17 % yield) were obtained whose optical spectra are in fact very similar to the literature spectra (Figure 4).…”

“…In fact, no distinction can be made between these two scenarios. However, since the 8), N2-ZnÀ O1 98.52( 7), N3-ZnÀ N4 86.94( 8), N3-ZnÀ O1 104.67 (8), N4-ZnÀ O1 102.37 (7). Thermal ellipsoids are set at 50 % probability.…”

“…Our investigations on the course of the templated one-pot isoporphyrin forming reaction have shown, that depending on the reaction conditions more or less significant amounts of different by-products form, which have to be separated elaborately by chromatography before the isolation of the desired products. [7] Since some of these by-products seem to react further during chromatography and work-up to yield new, distinct bands, the appearance of these component is directly related to the isolation effort and to the achievable yield of analytically pure isoporphyrins. In particular, we have found that a band at 640 nm as well as sharp absorptions around 480 nm become dominant when very polar conditions are present in the condensation step.…”

“…Only one of the two independent molecules in the asymmetric unit is shown. Selected bond lengths (Å) and angles (°): ZnÀ N1 2.073(2), ZnÀ N2 2.069(2), ZnÀ N3 2.071(2), ZnÀ N4 2.065(2), ZnÀ O1 2.134(2), N1-ZnÀ N2 87.06(8), N1-ZnÀ N3 159.39(8), N1-ZnÀ N4 89.53(8), N1-ZnÀ O1 95.92(8), N2-ZnÀ N3 89.02(8), N2-ZnÀ N4 159.07(8), N2-ZnÀ O1 98.52(7), N3-ZnÀ N4 86.94(8), N3-ZnÀ O1 104.67(8), N4-ZnÀ O1 102.37(7). Thermal ellipsoids are set at 50 % probability.…”