Unexpected effect of substituents on the zero-field splitting of triplet phenyl nitrenes

Abstract

The EPR spectrum of triplet 2,4,6-tribromophenyl nitrene was obtained in glassy methylcyclohexane at 15K. Surprisingly, the zero-field splitting parameter D=0.989cm−1 derived from this spectrum is much lower than that reported previously for triplet 3,5-diazido-2,4,6-tribromophenyl nitrene and has the same value as in phenyl nitrenes composed with light atoms. DFT calculations of the zero-field splitting parameters support this unexpected experimental observation. Experimental and theoretical data provide evidence that the enhanced by bromine atoms spin-orbit contribution to the parameter D (the so called “heavy-atom effect”) is strongly modulated by other substituents attached to the aromatic cycle.