Wavelength dependent photochemistry of expanded chromophore and asymmetric dibenzothiophene S-Oxide derivatives

Abstract

Irradiation of dibenzothiophene S-oxide (DBTO) is believed to generate ground state atomic oxygen [O(3P)]. The irradiation conditions and the efficiency of the deoxygenation event are not ideal when working with biological systems. Dinaphtho[2,1-b:1′,2′-d]thiophene S-oxide (DNTO) and several other analogs were shown to allow visible light to drive deoxygenation due to red-shifted absorbance of the DBTO derivatives. Additionally, DNTO and its analogs did not substantially improved quantum yield of deoxygenation (Φdeox.). To improve both Φdeox. and absorbance, changes were made to the DBTO scaffold. The first change was an addition of an electron withdrawing group (EWG) to weaken the SO bond strength of the sulfoxide to improve Φdeox.. The second change was the addition of an aromatic substituent to enhance and red-shift the absorbance. Common intermediate experiments were performed in toluene to examine if these new DBTO analogs produced a common oxidant under both UV and visible light irradiation. The separate light sources produced different product ratios suggesting these asymmetric DBTO derivatives have wavelength-dependent mechanisms of oxidation.