Early Excited State Dynamics of 6-Styryl-Substituted Pyrylium Salts Exhibiting Dual Fluorescence

Pigliucci, A.; Nikolov, P.; Rehaman, A.; Gagliardi, L.; Cramer, C. J.; Vauthey, E.
J. Phys. Chem. B 2006, 110, 9988.

A series of 6-styryl-2,4-diphenylpyrylium salts exhibiting dual fluorescence has been investigated by fluorescence up-conversion in conjunction with quantum chemical calculations. The short-wavelength emission is due to an excited state localised on the pyrylium fragment and the long-wavelength emission arises from a charge-transfer state delocalised over the whole molecule. The two fluorescing states do not exhibit a precursor-successor relationship. The rise time of the short wavelength fluorescence is smaller than 200 fs, while that of the long wavelength emission depends on the electron donating property of the styryl group substituent. The rise is almost prompt with the weaker donors, but is slower, wavelength and viscosity dependent with the strongest electron-donating group. A model involving a S₂/S₁ conical intersection is proposed to account for these observations.

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