Two-photon—induced fluorescence and electronic structure of substituted dicyanomethylene pyrans in solutions under femtosecond excitation

The method of two-quantum etalon is used to determine the two-photon absorption cross sections of eight dicyanomethylene (DCM) pyran dyes (DCM derivatives). Measurements of two-photon absorption of femtosecond Ti: sapphire-laser (λ = 800 nm, τ = 100 fs, and f = 89 MHz) radiation have been carried out. The nature of nonlinear excitation has been confirmed by the dependence of the fluorescence intensity on the excitation radiation intensity, which is close to a square-law one. Based on the measured two-photon absorption cross sections, the sizes of delocalized π-electronic clouds of DCM dye molecules with different substitutes are estimated in solvents with different polarity parameters. It is demonstrated that an increase in the polarity parameter of the solvent causes the two-photon absorption cross sections and sizes of delocalized π-electronic clouds of DCM, DCM-doa, DCM-17, DCM-5M, and DCM-11 dyes to increase. It is demonstrated that the size of the delocalized π-electronic cloud and the quantum fluorescence yield of the DCM-ul dye decrease with increasing polarity of the solvent despite the growth of the two-photon absorption cross section. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 69–73, November, 2005.