β‐meso‐Annulated meso‐Tetraarylchlorins: A Study of the Effect of Ring Fusion on Chlorin Conformation and Optical Spectra

Abstract

AbstractChlorins are a class of reduced porphyrins with a very intense longest wavelength Q band (Qy) in the red region, due to their non‐planar conformations. This fact is useful in fields like photodynamic therapy and organic photovoltaics, which rely upon the long wavelength absorptivity of the photosensitizing dyes. Here, we have reviewed the synthesis and optical properties of many novel β‐meso‐annulated chlorins, which possess bathochromic shifts in their optical spectra, compared to their non‐fused analogues. In general, we find that these red‐shifts are promoted by planarization of the macrocycle caused by β‐meso‐ring fusion. However, in select examples of ring‐fused chlorins bearing an additional non‐pyrrolic subunit, in fact we see strong deviation from planar conformation contrary to the general trend. These molecules show Qy bands in the NIR region, but with reduced absorptivity.