Photochemistry of 1-cyanonaphthalene/triethylamine van der Waals complex: Intermolecular exciplex formation under collision free conditions

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Abstract
The van der Waals complex of 1-cyanonaphthalene with triethylamine exhibits fluorescence from the intermolecular exciplex upon electronic excitation. The efficiency of exciplex formation is strongly excitation energy dependent. The excitation of the complex into the origin band shows resonant emission, while excitations into vibronic bands with excess vibrational energies >400 cm−1 lead to the exciplex formation. The exciplex formation efficiency is also dependent on isotopic substitution in 1-cyanonaphthalene. The barrier to the exciplex formation is larger for the deuterated complex. The fluorescence excitation spectrum of the exciplex reveals that the exciplex formation process is favored over other intramolecular relaxation processes over the excess energy range 700–1500 cm−1. These results suggest that van der Waals complexes can be important intermediates in the intermolecular exciplex formation in the vapor phase.