Highly luminescent anthracene sulfides. Synthesis, experimental and DFT study of their optical properties and interaction with electron deficient nitroaromatic compounds

Abstract

We report on the synthesis, thermal and photooxidative behavior and optical properties of a series alkyl and aryl sulfides with anthracene cores. All anthracene sulfides studied here were highly fluorescent. Their optical behavior was compared with that of related pyrene bisulfide and tetrasulfides. All sulfides are crystalline compounds and show good chemical stability in condensed phase. In solution, the pyrene derivatives are very stable but the anthracene derivatives suffer a slow photooxidation process under air and ambient light. While the bisulfides of anthracene and pyrene have very different spectroscopic behavior, the tetrasubstituted anthracene and pyrene sulfides exhibit quite a few similarities. Thus, the chromophoric core of the compounds consists of the aromatic core and the sulfur or oxygen atoms, so the variation from alkyl to aryl substituents does not alter the profiles of the absorption and emission spectra. All they show intense fluorescence, but sulfides bearing SCH2 or OCH2 groups display higher fluorescence efficiencies than the ones with aryl substituents. In addition, their quenching efficiencies with nitroaromatic compounds of both series are dominated by steric hindrance rather than by electronic factors. Bathochromic shifts in the absorption spectra are well reproduced by TDDFT. Moreover, calculations indicate that the lower energy excitations are of non-ionic type in agreement with experimental results which showed that both absorption and emission spectra are devoid of noticeable solvatochromic effects.