EPR Study of the Triplet Excitons in a Single Crystal of DDQ Tetraethylammonium Ion Radical Salt.

The EPR spectra of the triplet excitons in a single crystal of tetraethylammonium 2,3-dichloro-5,6-dicyano p-benzosemiquinone are studied in detail. Principal values and directions of the fine structure tensor D and of the g tensor are obtained and discussed. The spin distribution in the dimers is shown to be the same as in the isolated molecules by comparing the g factor of the triplet exciton with that of the radical in solution and by comparing the experimental D tensor with the calculated one with spin densities which describe the unpaired electron in the isolated molecule. From the temperature dependence of the EPR spectrum the triplet exciton activation energy ET = 0.37 eV, the exciton—exciton exchange activation energy Ew = 0.41 eV, the intra- and inter-stacks exciton hopping frequency μj = 1.6 × 104 MHz and μt = 0.2 MHz are obtained. fa]This work was supported in part by the National Research Council of Italy (C.N.R.) through its Centro di Studio sugli Stati Molecolari Radiacalici ed Eccitati. © 1980, All rights reserved.