Synthesis of a doubly SO2-fused phlorin: Tuning the structure and properties by the SO2 groups

Abstract

A doubly SO2-fused phlorin 4 has been synthesized by the [2 + 2] condensation of dipyrromethanecarbinol 2 and SO2-fused dipyrromenthane 3 in the presence of TFA, followed by DDQ oxidation. The SO2-fused phlorin 4 has been characterized by absorption, fluorescence, mass and NMR spectra, as well as X-ray analysis. Compared to the [Formula: see text]-unsubstituted phlorin 5, the SO2-fused phlorin 4 exhibits a red-shifted absorption spectrum (around 12 nm), a more distorted molecular conformation, as well as nice photostability even with an electron-donating meso-3,5-di-tert-butylphenyl group. The titration of 4 and 5 with TBAF has been monitored by absorption spectroscopy. The deprotonated phlorin 4 shows a peak at 870 nm which is red shifted by 26 nm compared to that of deprotonated 5.