Interchain interaction and Davydov splitting in polythiophene crystals:: An ab initio approach

The crystal-induced energy splitting of the lowest excitonic state in polymer crystals, the so-called Davydov splitting Delta, is calculated with a first-principles density-matrix scheme. We show that different crystalline arrangements lead to significant variations in Delta, from below to above the thermal energy k(B)T at room temperature, with relevant implications on the luminescence efficiency. This is one more piece of evidence supporting the fact that control of interchain interactions and solid-state packing is essential for the design of efficient optical devices. (C) 2002 American Institute of Physics.