Steady State and Dynamic Photophysical Properties of 2-Benzoimidazoleacetonitrile- α-Phenylmethylenes and 1-Aryl-2,2-Dicyanoethenes

The steady state and dynamic photophysical characteristics of newly synthesized 2-benzoimidazoleacetonitrile- α-phenylmethylenes (BIA’s) and 1-aryl-2,2-dicyanoethenes (DCE’s) have been investigated in solution at 300 K and in a frozen matrix at 77 K. The compounds have a very low or no emission in solution at 300 K both in non-polar and polar solvents. While in BIA’s a significant fluorescence ability is registered in a frozen ethanol matrix at 77 K, freezing solutions of DCE’s at 77 K does not lead to the appearance of either fluorescence or phosphorescence at 77 K even in the presence of C2H5J. The comparison of the fluorescence ability in aprotic and protic solvents does not show any evidence for the specific influence of the protondonating ability of the solvents on the weak fluorescence caused by the formation of intramolecular hydrogen bonds in excited states. The high fluorescence quantum yield of BIA’s in a frozen matrix at 77 K indicates that intramolecular libration of two heavy groups in the allyl chain is the reason for the weak fluorescence at 300 K. Quantum-chemical calculations support the hypothesis of quenching processes in the excited state of BIA’s at 300 K.