Influence of hydrostatic pressure and temperature on two-photon absorption of a C60-2-thioxo-1,3-dithiole cycloadduct

Two-photon absorption (TPA) at lambda=532 nm versus applied hydrostatic pressure (p) (up to 20 GPa) and temperature (T) (in the 77-300 K range) was used to study intermolecular dynamics in powderlike fullerene-1,3-dithiolic adduct and C-60 systems. For C-60-1,3-dithiole adduct, we observed a sharplike maxim of the TPA versus p-T below 230 K. Comparing the obtained results with those of C60, we have unambiguously shown that the observed behaviors are connected with the adding of the 1,3-dithiole core. To explain the experimental results, we performed ab initio molecular-dynamics geometry optimization, taking into account the superposition of all possible molecular conformations with appropriate weighting factors and higher-order intermolecular multipole interactions. We have shown an increase of the absolute value of the TPA coefficient in the C-60 cycloadduct by more than 30%. This fact is mainly caused by the asymmetry of intramolecular electronic charge-density asymmetry. The modulatedlike dependence of the TPA versus p and T have been observed. The latter one reflects the vibration and rotational contributions to the TPA values. [S0163-1829(99)07713-9].