Photoluminescence efficiency of substituted quaterthiophene crystals

The photoluminescence (PL) efficiency of substituted alpha -conjugated quat erthiophene crystals shows marked differences depending on crystal packing and molecular geometry. This effect is studied by evaluating the role of th e intermolecular interactions and the effects of the single molecule confor mation on the intersystem crossing (ISC) rate. The comparison of these calc ulations with absolute quantum effciency measurements and with the experime ntal temperature dependence of the PL decay time, indicates that the differ ences in PL efficiency are not inherent to crystal packing effects but they an determined by the ISC rate.