The excimer formation and photodissociation in jet-cooled molecular clusters of 1-cyanonaphthalene (1-CNN) and its deuterated compound (1-CNN-d(7)) were investigated. The jet-cooled excimer fluorescence was observed in the excitation cluster band (n greater than or equal to 4) of 1-CNN-d7 as well as of 1-CNN. The excitation of the excimer at 700-750 nm results in a considerably strong depletion of the excimer fluorescence and a simultaneous fragment fluorescence of the clusters at 335-350 nm. An excimer depletion spectrum was observed at 700-750 nm from the wavelength dependence of the depletion laser of the fragment intensity. Comparison of the excimer depletion spectrum of the jet-cooled cluster with that of the transient absorption of the excimer in solution suggests that the excitation into the upper state of the excimer induces the photodissociation of the excimer and the simultaneous fluorescence of the fragment. Fluorescence decay times of the fragment by the excimer depletion were considerably larger than those of the monomer and smaller than the dimer＇s. The photodissociation mechanism of the excimer was discussed in terms of decay times of the fragment fluorescence and the unexpectedly stable dimer core of 1-CNN.