Location of a1Agstate in bithiophene

摘要

The 0ndash;0 excitation energy of a1Agstate of 2,2rsquo;hyphen;bithiophene has been determined by measuring the twohyphen;photon fluorescence excitation spectrum of a dilute solution of this molecule in crystallinenhyphen;hexane at 77 K. Because the 0ndash;0 energy is what would have been predicted by extrapolating previously measured agr;,ohgr;hyphen;dithienylpolyene 2thinsp;1Ag0ndash;0 energies to zero polyene chain length, it is assigned to the 2thinsp;1Agstate. The 0ndash;0 band is centered at 36thinsp;173 cmminus;1, approximately 6570 cmminus;1above the 0ndash;0 of the 1thinsp;1Agto 1thinsp;1Butransition. This order of bithiophene excited singlet states is opposite to that of the linear polyene with the same number of double bond but may reverse for chains longer than six repeat units.