A theoretical study of the ring size effect on one- and two-photon absorption properties of macrocyclic thiophene derivatives

Abstract

The equilibrium geometries, electronic structures, one-and two-photon absorption (OPA and TPA) properties of macrocyclic thiophene derivatives [C[6T_A_E] n -Me (n = 1-3)] with different ring sizes have been investigated by quantum chemistry calculation. The results indicate that as the unit number increases, the p-conjugated effect enhances, OPA maximum wavelength (l (1) max ) shows a significant red-shift with increasing oscillator strength (f 0k ), and the TPA cross-section value (d max ) also increases, the d max value of C[6T_A_E] 3 -Me is twentyfold larger than that of the repeat unit C[6T_A_E]-Me. We have analyzed the internal factors influencing d max such as transition dipole moments (M 0k and M kn ), the product of oscillator strengths (f 0k  f kn ), and the number of p electrons (Ne) in detail. In addition, it is demonstrated that intramolecular charge transfer (ICT) is one of the intrinsic factors, but not a dominant one for the increase in TPA cross-section with regard to this system.