Investigations of the heavy atom effect occurring in bianthryl and 10,10 '-dibromobianthryl. Fluorescence, cyclovoltamperometric and actinometric studies

摘要

A preliminary study of photophysical and photochemical properties of 9,9'-bianthryl (BA) and 10,10'-dibromo, 9,9'-bianthryl (DBrBA) is presented. Dual fluorescence occurring in bianthryl (BA) has been investigated in solvents containing heavy atoms, such as chlorine, bromine and iodine. The presence of heavy atoms reduces strongly the uorescence lifetimes and the uorescence quantum yields of BA, the effect is strongest in ethyl iodide, i.e. in the solvent containing the heaviest atom, iodine. On the other hand, it has been found that introduction of two heavy atoms ( bromine) into the bianthryl molecule modifies noticeably its uorescence properties, which indicates existance of an internal heavy atom effect. Again, a reduction of the uorescence lifetime and the uorescence quantum yield, compared to the parent molecule, has been observed. On the basis of these observations the mechanism of (CT)-C-1 double right arrow (LE)-L-3 intersystem crossing has been discussed. In BA the rate determining process is a reversible spin inversion within the radical pair. In DBrBA where the spin flip is accelerated by the presence of heavy atoms (bromines) the spin-allowed electron transfer (CT)-C-3 double right arrow (LE)-L-3 becomes important in the overall intersystem crossing process. It has been found that DBrBA undergoes a photoreduction in the presence of aromatic donors, such as amines, leading finally to BA. Similar reaction seems to be observed in electrochemical measurement. The reduction of DBrBA originates from the primary electron transfer process either photoinduced or electrochemical leading to the free anion radicals of DBrBA. [References: 45]