We report on laser-induced fluorescence excitation and dispersed fluorescence spectra of two isomeric compounds: 1,4- and 1,8-diazatriphenylene (1,4- and 1,8-DAT) isolated in supersonic molecular jets, and their 1:1 complexes with protic solvents. We found that the ground and excited state vibronic patterns of bare 1,4-PAT differ significantly from those of 1,8-DAT, and those of the complexes of both isomers. A marked activity of several out-of-plarie vibrations in 1,4-DAT and the symptoms of the distortion. of the S-1 excited molecule were diagnosed from the vibronic spectra, whereas planar structures were predicted for 1,8-DAT in S-0 and S-1 states. An anharmonic double-minimum potential along an out-of-plane coordinate has been derived and used to predict higher overtones of the S-1 state vibration at 113 cm(-1). Large enhancement of fluorescence was observed upon formation of 1:1 complexes of 1,4-DAT with water or methanol, which is explained in terms of an increased separation of interacting (n,pi*) and (pi,pi*) electronic states in the H-bonded complexes, and/or a suppression of the intersystem crossing. process.