Nanosecond Flash Photolysis Studies of Intersystem Crossing Rate Constants in Biradicals: Structural Effects Brought about by Spin Orbit Coupling

摘要

This paper concerns the structural effects of spin-orbit coupling (SOC) as a mechanism of intersystem crossing (isc) in triplet-derived biradicals. First we show that SOC is strongly enhanced in biradicals with an acyl terminus relative to biradicals with only hydrocarbon termini. Second, we present evidence that, even for long chains, biradicals containing an acyl terminus prefer to undergo isc in conformers with small end-to-end distances. This appears to be a direct result of the dominance of SOC over electron-nuclear hyperfine coupling (HFC) in the isc process.