Electronic excited states and luminescence properties of palladium(II)corrin complex

Abstract

The DFT and TD-DFT calculations were performed for palladium(II)1,2,2,7,12,12-heptamethylo-15-cyanocorrin complex ([Pd(II)HM-CN-corr]+). Experimentally [Pd(II)HM-CN-corr]+ exhibits a weak fluorescence and strong phosphorescence. For the [Pd(II)HM-CN-corr]+ complex the electronic spectrum was calculated using the BP86 and B3LYP functionals. The results shows that BP86 gives electronic transition energies in good agreement with the experiment, while B3LYP overestimates the calculated transition energies, which can be related to the order and energy of molecular orbitals. Therefore, the BP86 functional was used in further calculations. The presence of the solvent was taken into account by the use of the COSMO model. The spin-orbit (SO) states were calculated along the PEC determined by N-Pd-N bending angle active coordinate in the S1 using the ZORA method. The rate constants of fluorescence, phosphorescence and intersystem crossing processes were determined. Based on calculations the photophysical processes occurring in [Pd(II)HM-CN-corr]+ can be explained. After light absorption there is excitation to the S1 or S2 states and then the internal conversion to S1 state from S2. Comparison of the calculated rate constants of fluorescence (3.3·107 s-1) and ISC to the close lying T2 state (8.5·1010 s-1) in the S1 minimum shows that the ISC is more probable. This is an explanation why fluorescence in [Pd(II)HM-CN-corr]+ is weak. The vibrationally resolved fluorescence and phosphorescence band shapes were determined using the Franck-Condon approximation. The obtained band profiles agree qualitatively with the experimental ones. The most important molecular vibrations contributing to vibrational bands were determined. The calculated rate constants values and the obtained picture of photophysical processes agree qualitatively with the experimental data.