Polarized twohyphen;photon fluorescence excitation studies of pyrimidine

摘要

Twohyphen;photon fluorescence excitation studies are reported for pyrimidine (1,thinsp;3hyphen;diazine) dissolved in a hexane solution at room temperature. Quantitative twohyphen;photon absorption strengths for the three lowest electronic absorption bands are measured relative to the benzeneB2uthinsp;larr;thinsp;A1gtwohyphen;photon transition. TheB1(npgr;ast;)thinsp;larr;thinsp;A1excitation profile matches the onehyphen;photon absorption band closely, indicating an allowed twohyphen;photon transition. However, theB2(pgr;pgr;ast;) twohyphen;photon intensity is vibronically induced by a 1600 cmminus;1b2vibration, even though transitions into this state are formally twohyphen;photon allowed. In addition, polarization analysis is used to uncover a new transition in pyrimidine in a region of overlapping absorptions. This new transition is assigned to the lowestA2(npgr;ast;) state. If this assignment is correct, theA2(npgr;ast;),B1(npgr;ast;) splitting is 1.4 eV. Spectroscopic CNDO and INDO calculations of the twohyphen;photon absorption strengths are also reported.