The synthesis and examination of some fluorescent derivatives of 2,2′-bithienyl and 2-(2′-furyl)-thiophen

Abstract

Derivatives of 2,2′-bithienyl with a carbonyl-containing substituent, COR (R = H, Me, OH, OMe, NH₂, etc.), at the 5-position (1) are highly fluorescent in hydrogen-bonding solvents. The effect on the emission process produced by replacement of either or both thiophen moieties by furan has been investigated. Whilst a derivative of 2-(2-furyl)thiophen with a formyl group at the 5-position (7) gives rise to a blue fluorescence similar to that of the corresponding bithienyl, 2-(5-formyl-2-furyl)thiophen (6) and two 5-acyl-2,2′-bifuryls (2) and (3) were found to be almost nonfluorescent.

The influence of solvent on the fluorescence of 5-acyl-2,2′-bithienyls has been examined in detail. A relation between solvent hydrogen-bonding character and the wavelengths of emission and absorption suggests that fluorescence arises from a charge-transfer excited state. Relative fluorescence efficiency also shows a pronounced dependence on the hydrogen-bonding properties of the solvent. Possible explanations for this behaviour have been put forward.