Stability, optical and charge transport properties of saddle-shaped cyclooctatetrathiophene (COTh) isomers: a theoretical study

Design and structure–property relationship studies of the system containing a cyclooctatetraene (COT) ring fused with four 5-membered heterocyclic rings have been reported. The five-membered heterocycle chosen for the present study is thiophene and based on connectivity with COT, cyclooctatetrathiophene (COTh) exists in fifteen geometrical isomers. The systematic reviews of all the isomers of COTh, are carried out by utilizing density functional theory (DFT) and time dependent-density functional theory (TD-DFT) calculations. Electronic excitations, reorganization energies (transport properties of electron and hole), electron affinities (EA) and ionization potentials (IP) of all the isomers are reported. Based on the outcomes of this study, we suggest that one of the isomers, among all fifteen possible isomers, is better suited for applications that take advantage of its charge transport properties.