A series of quantum calculation have been done to investigate the excited state property of laser dye molecule LDS751 by density function theory. The possible configuration and processes have been predicted by the theoretical point of view. Two major isomization pathways which may have influence on the excitation spectral property have been analyzed, it is indicated that rotation corresponding to the bridge C—C bond and terminal C—N maybe the comparable reaction channels in the first excited state. The intramolecular charge transfer and the degree have been estimated by the comparison of the summary of the charge re-distribution during different function group in the excitation. The conclusion can give some evidence and support to the relative absorption and emission spectra in different time scale experimental investigation.

Key words: dye molecule, conjugation, charge transfer, photo-isomerization