Intermolecular dynamics and exciplex formation of the 1-cyanonaphthalene/triethylamine van der Waals complex

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Abstract
The exciplex formation dynamics of the 1-cyanonaphthalene/triethylamine van der Waals complex upon excitation has been examined under collision free conditions. Mode-specificity has been found in the excitation of a combination band between intra- and intermolecular vibrational modes in the S1 state of the vdW complex to promote the exciplex formation reaction. The specificity is lost at higher excess energies since randomization of energy among intermolecular modes is more extensive than the reaction rate. The fluorescence decays of the S1 and exciplex states have been measured as a function of excess vibrational energy above the S1 origin. The lifetime of the S1 state at the excess energy where the mode-specific reaction is observed is different from that of the exciplex fluorescence. As the excess energy increases, the decay rate of the S1 state shows a sharp increase due to the exciplex formation while the exciplex fluorescence rate remains constant. The observed decay rate constants have been discussed using a simple kinetic model which accounts for the mode-specific exciplex formation.