OPTICAL-SPECTRA OF ISOLATED S-CIS-BITHIOPHENE AND S-TRANS-BITHIOPHENE - TORSIONAL POTENTIAL IN THE GROUND AND EXCITED-STATES

Fluorescence excitation and fluorescence spectra of 2,2'-dithenyl (commonly known as bithiophene) seeded into a supersonic helium expansion show complete vibronic resolution. The fluorescence excitation spectrum has two components whose relative intensity depends on expansion conditions. Measurement and analysis of these spectra for systematic variation of expansion conditions leads to their assignment to the s-trans and s-cis conformers and provides information on the potential for s-trans to s-cis interconversion in the ground and first excited singlet states.