Photodeoxygenation of dinaphthothiophene, benzophenanthrothiophene, and benzonaphthothiophene S-oxides

Abstract

Photoinduced deoxygenation of dibenzothiophene S-oxide (DBTO) has been suggested to release atomic oxygen [O(³P)]. To expand the conditions and applications where O(³P) could be used, generation of O(³P) at longer wavelengths was desirable. The sulfoxides benzo[b]naphtho-[1,2,d]thiophene S-oxide, benzo[b]naphtho[2,1,d]thiophene S-oxide, benzo[b]phenanthro[9,10-d]thiophene S-oxide, dinaphtho[2,1-b:1′,2′-d]thiophene S-oxide, and dinaphtho[1,2-b:2′,1′-d]thiophene S-oxide all absorb light at longer wavelengths than DBTO. To determine if these sulfoxides could be used to generate O(³P), quantum yield studies, product studies, and computational analysis were performed. Quantum yields for the deoxygenation were up to 3 times larger for these sulfoxides compared to DBTO. However, oxidation of the solvent by these sulfoxides resulted in different ratios of oxidized products compared to DBTO, which suggested a change in deoxygenation mechanism. Density functional calculations revealed a much larger singlet–triplet gap for the larger sulfoxides compared to DBTO. This led to the conclusion that the examined sulfoxides could undergo deoxygenation by two different mechanisms.