Journal of Physical Chemistry A, Vol.101, No.11, 2083-2088, 1997
Effects of Additional Linkers in Biphenyl-4,4’-Dinitrene on the Low-Lying Singlet-Triplet Energy-Gap and Zero-Field Splitting
Perturbation effects of additional linkers on the spin-spin coupling in biphenyl-4,4’-dinitrene (1) were examined by introducing a linking group between 2- and 2’-positions of 1. Five different doubly linked systems showed triplet ESR spectra corresponding to quinonoid dinitrenes. Curie law analyses suggested that all those tripler states were thermally excited triplet states. In addition, the singlet-tripler energy gaps, which were determined by the Curie law analyses, were well, correlated with their corresponding zero-field-splitting (zfs) D values. The result could be explained by the stability of dinitrene character which is estimated from the resonance energy of the intervening pi-system. Our semiempirical molecular orbital calculations supported the experimental correlation between the singlet-triplet energy gap and the zfs D value.
Keywords:SEMIEMPIRICAL METHODS;RESONANCE ENERGIES;OPTIMIZATION;HETEROCYCLES;AROMATICITY;PARAMETERS;EXCHANGE