Computational study of the one- and two-photon absorption properties of macrocyclic thiophene derivatives

The geometrical structure, electronic structure, one-photon and two-photon absorption properties of a series of macrocyclic thiophene derivatives C[3T_DA]n (n = 2–5) have been studied using density functional theory (DFT) and Zerner’s intermediate neglect of differential overlap (ZINDO) methods theoretically. The results showed that the range of λ(1)maxs is 390–470 nm and λ(2)maxs is 640–670 nm, while, both λ(1)max and λ(2)max gradually enlarge as increasing the number of the C[3T_DA] unit. And C[3T_DA]n compounds exhibited large TPA cross-section (δmax), and the factors influencing on the δmax values were analyzed in detail. Transition dipole moments M0k and Mkn play important roles on δmax. Both π-electron number (Ne) and the product of oscillator strengths from ground state to mediate state (ƒ0k) and from mediate state to final state (ƒkn) are in proportion to δmax. Moreover, δmax linearly depends on the static second-order nonlinear optical susceptibilities (β0).

► The one- and two-photon absorption spectra, TPA transitions and TPA cross-sections of macrocyclic thiophene derivatives C[3T_DA]n (n = 2–5) have been explored in detail on basis of the stable π-conjugated structures using DFT combing with ZINDO and FTRNLO programs.
► Since their one- and two-photon absorption spectra locate at different windows, they will have a potential application in the TPA dynamic therapy.
► Moreover, the TPA cross-section (δmax) of C[3T_DA]5 (8997.2GM) is about 18 times bigger than that of C[3T_DA]2, in which transition dipole moments (M0k, Mkn), π-electron number (Ne), the product of oscillator strengths (ƒ0k × ƒkn), static second-order nonlinear optical coefficient (β0), and the thiophene and acetylene unit in each compound all play important roles on the increasing of δmax.
► It is suggested that this series of macrocyclic thiophene derivatives will be candidates in practical two-photon materials.