Femtosecond polarization resolved spectroscopy: A tool for determinationof the three-dimensional orientation of electronic transition dipolemoments and identification of configurational isomers

摘要

A method is presented that combines femtosecond polarization resolved UV/visible pump—IR probespectroscopy and density functional theory calculations in determining the three-dimensionalorientation of an electronic transition dipole moment (tdm) within the molecular structure. Themethod is demonstrated on the approximately planar molecule coumarin 314 (C314) dissolved inacetonitrile, which can exist in two ground state configurations: the E- and the Z-isomer. Based onan exhaustive search analysis on polarization resolved measurement data for four differentvibrational modes, it is concluded that C314 in acetonitrile is the E-isomer. The electronic tdmvector for the electronic S_0→S_1transition is determined and the analysis shows that performing theprocedure for four vibrational modes instead of the minimally required three reduces the 1σprobability area from 2.34% to 2.24% of the solution space. Moreover, fastest rotationalcorrelation time τ_c for the C314 E-isomer is determined to be 26 ± 2 ps.