π-Conjugated Molecules Containing Naphtho[2,3-b]thiophene and Their Derivatives: Theoretical Design for Organic Semiconductors

We performed a theoretical investigation on a series of pi-conjugated organic molecules containing naphtho[2,3-b]thiophene and their derivatives using density functional theory calculations. All molecules considered exhibit planar structures and aromaticity. Energy levels of frontier orbitals and reduction and oxidation potentials of these compounds predicted by our solvation model reveal good agreement with available experimental values. The UV absorption spectra point out a clear trend that maximum peaks corresponding HOMO-LUMO transitions are red-shifted: (i) from compounds containing 0 to those containing Se, (ii) from dimers 1a-3a and 1b-3b to timers 4a-6a and 4b-6b, and from parent compounds 1a-6a to perfluorinated derivatives 1b-6b. Parent compounds 1a-6a can be considered as p-type semiconducting materials with low reorganization energies, high transfer integrals, and hole mobility. Perfluorinated compounds 1b-6b are suggested to be very good candidates for ambipolar semiconducting materials. Introduction of fused-ring core molecules considerably improves the charge transport characteristics of the co-oligomers 4a-6a and 4b-6b as compared to those of corresponding molecules 1a-3a and 1b-3b. Accordingly, the former have lower reorganization energies, higher electron transfer integrals, and higher rates of charge hopping.