The UV photodissociation of the C4H4N2, C4H4N2 and C6N4 molecules have been investigated. Laser-induced fluorescence (LIF) was used to study the nascent internal energy distribution of the ON radicals produced by photolysis of the above molecules at 193 nm. Tha 0-0 band rotational distributions of the X32+ state of CN radical can be described by a Boltzmann distribution foi all of these molecules. The rotational temperatures for v"=0 level of ON(X) are 1680+40, 2000+50 and 1470+30K for G4H4N2, C4H2N2 and G6N4, respectively. The rotational temperature of the 1-1 band is 1150+160K for C4H2N2 molecule. The gas phase UV absorption spectra of these molecules were measured.