Coherence in electronically excited dimers. III. The observation of coherence in dimers using optically detected electron spin resonance in zero field and its relationship to coherence in one-dimensional excitons

The observation of coherent dimers in their excited triplet state is reported for a molecular crystal of 1,2,4,5-tetrachlorobenzene at low temperatures (below 4.2 K). Utilizing the theory developed in our previous paper, the coherence time (10^-6 sec) and the anisotropy of the resonance interactions in the excited state were established. The identification of the dimer as translationally equivalent, from the zero-field optically detected magnetic-resonance spectra, establishes the effective dispersion for the triplet exciton band of the neat crystal. Morover, the magnitude of the resonance transfer time was shown to be much less than the coherence time: the dimer is coherent for a period of 10^5 times that associated with the stochastic limit.