Ground and low-lying excited electronic states of [3,3'] bidiazirinylidene (C2N4).

The second-order generalized Van Vleck perturbation theory (GVVPT2) variant of multireference perturbation theory was used to investigate the ground and low-lying excited electronic states of [3,3'] bidiazirinylidene (C(2)N(4)). C(2)N(4) is arguably the simplest molecule with multiple CN(2) rings. Equilibrium geometries and adiabatic energy differences of the 1(1)A(g) ground state and 2 (1)A(g), 1(1)B(1g), 1(3)B(1g), 1(1)B(2g), 1(3)B(2g), 1(1)B(3g), 1(3)B(3g), 1(1)B(2u), 1(3)B(2u), 1(1)B(3u), and 1(3)B(3u) excited states of D(2h) symmetry were obtained. In addition, vertical excitation energies to and emission energies from the excited states were obtained. The 1(1)A(g) optimized geometry and harmonic frequencies for the CN(2) rings in C(2)N(4) are similar to those for the related difluorodiazirine molecule: R(CN), R(NN) bonds and the angleNCN angle are 0.012 and 0.006 A longer and 0.8 degrees smaller than that for the ring in F(2)CN(2). The NN stretch frequencies are 1470 and 1562 cm(-1), and CN stretches are 993 and 995 cm(-1). The similarity between the GVVPT2 results of C(2)N(4) and F(2)CN(2) suggests that C(2)N(4) might be sufficiently stable to be synthesized. The lowest-energy spin- and electric dipole-allowed vertical excitation, to the 1(1)B(2u) state, is predicted to occur in the visible (2.30 eV, 538.9 nm).