Electronic spectra of the organic charge transfer salts TTT-In [antikvár]

Charge transfer complexes formed by the donor tetra- thiotetracene (TTT) and halogen acceptors have conducti- •i vities among the highest observed in organic solids . The TTT-I system was studied recently by X-ray and by con- n 2 3 4 2 ductivity experiments ' ' . Buravov et al reported two phases, one corresponding to composition n'V 1 (phase A) and another, called phase B to nw 1.5» Phase B has a metallic conductivity at high temperatures, and it remains high even at liquid He temperatures. The ability of iodine to form stable counterions I~ and triiodide and also the possibility of inclusion of neutral I2 molecules into the crystal is expected to be responsible for multiple phases with different electronic and magnetic properties. We discuss the optical properties of TTT-In observed both in solution and in the solid state, and also present single crystal conductivity data of the different phases. TTT-In was prepared by reacting TTT and iodine in nitrobenzene, the iodine concentration was varied in the 2 mole/mole TTT. solution between 0 and The solution was cooled from 210°C to room temperature at a rate 5°C/min. The was material obtained, recrystallized from nitrobenzene with a cooling rate as given above. Before recrystallization the iodine concentration was not very different from that in solution, but recrystallization resulted in a convergence of the iodine concentration to certain composition ratios, and in well developed crystals with good morphology.