Spectroscopy and Photophysics of Low-Lying Excited Singlet States of α,ω-Dithienylbutadiene and α,ω-Dithienylethylene Vapors

Fluorescence and excitation spectra and fluorescence lifetimes have been measured for α,ω-dithienylbutadiene (DTB) and α,ω-dithienylethylene (DTE) in a jet-cooled He expansion and in the static vapor phase. It is shown that the emission of DTB in the static vapor phase consists of the S1(21Ag) and S2(11Bu) fluorescence, while the emission in a jet consists of solely the S1 fluorescence. The fluorescence quantum yields of DTB and DTE vapors decrease significantly with increasing excitation energy. The conformer-specific fluorescence was measured for DTB and DTE in a jet. The false S1 (21Ag) origin of the most stable conformer of DTB was observed at 25470.5 cm−1 in a jet, which is located approximately 2800 cm−1 below the S2 (11Bu) origin. The S1 origins of the two conformers of DTE were observed at 28648 and 28966 cm−1 in a jet, and the S1 state of the most stable conformer is assigned as 11Bu.