Influence of deuteration on the order–disorder phase transition of anthracene–tetracyanobenzene

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Abstract
Raman measurements of intermolecular vibrational frequencies, differential scanning calorimetry, and ESR measurements of triplet excitons are reported for crystalline anthracene–tracyanobenzene and various deuterated analogs. Deuteration of all the α- or all β-anthracene positions lowers the temperature of the order–disorder transition by 10–12 K. Perdeuteration lowers it by 17 K. The effect may result from decreased repulsive interactions when the CH bond is replaced by the shorter CD bond. High excitation light intensities can change the apparent transition temperatures and expand the measured coexistence range of the high- and low-temperature phases. (AIP)