Extended triplet excitons in K+TCNQ−

By means of ESR, two types of triplet excitons have been discovered in K⁺TCNQ^? crystals, corresponding to the two independent rows of TCNQ^? ions in the crystal structure of this compound. The orientational dependence of the dipolar splittings at ?46°C and intensity measurements as a function of temperature are presented. The zero field splitting parameters are small and therefore the excitons must be large with respect to a lattice parameter. The extended nature of the excitons indicates, that either the electron electron repulsions are relatively small with respect to the one electron bandwidth in this material or that the alternation of the interionic distances is small.