Estimation of the site-energy difference in the crystal of tetraethylammonium(dimethyltetracyano-p-quinodimethanide)2 (Et4N(DMTCNQ)2)

We determined the fractional charge of DMTCNQ in the crystal of anion radical salts Et4N(DMTCNQ)2 as Et4N+(A−0.6B−0.4) combining the frequency shift of the Raman active CC stretching mode with the calculation of Madelung energy, where A and B represent DMTCNQ in the crystallographically independent sites. We estimated the site-energy difference between A and B from the analysis of the reflection spectrum of the charge-transfer band. The site-energy difference estimated from the calculation of the Madelung energy was comparable with this experimentally estimated value 0.082 eV.