Geometry and torsional motion of biphenyl in the ground and first excited singlet state

摘要

The lowest excited singlet state of biphenyl (BP) and a number of its isotopically and chemically substituted analogs have been studied by supersonic jet laser spectroscopy. The symmetry species of this excited state in BP can be classified asB+2uin theG16extended molecular symmetry groupG16(EM). The symmetryhyphen;allowed origin of the biphenyl hyphen;h10S1larr;S0electronic transition occurs at 35thinsp;268 cmminus;1. The frequency of the torsional motion inS1is determined to be sim;65 cmminus;1. The potential parameters for this motion inS1areV2=1195 cmminus;1,V4=minus;190 cmminus;1, andV6=18 cmminus;1. The torsional motion for the ground state (sim;50 cmminus;1) can be described byV2=50 cmminus;1andV4=minus;148 cmminus;1. The change in the dihedral angle between the two benzene rings in BP uponS0toS1excitation is determined to be sim;44deg; based on a Franckndash;Condon factor calculation. Several fundamentals of the molecular vibrations are assigned in theS1state. The exciton interaction between the coupled benzene rings in biphenyl is suggested to be large (103cmminus;1).