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 (com monly known as bithiophene) seeded into a supersonic helium expansion show complete vibronic resolution. The fluorescence excitation spectru m has two components whose relative intensity depends on expansion con ditions. Measurement and analysis of these spectra for systematic vari ation 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.