Probing optical properties of thiophene derivatives for two-photon absorption

We report a state-of-the-art characterization of the linear and nonlinear optical properties of two recent synthesized organic dyes based on the 2,5-dithienylpyrrole motifs. In particular after a careful conformational search was performed, the absorption spectra have been obtained at time-dependent density functional theory level taking into account vibrational and dynamical effects via a Wigner exploration of the potential energy surface. Furthermore, the excited state topology and electronic density reorganization have been characterized using natural transition orbitals and the charge transfer character quantified through recent developed descriptors, also allowing for the rationalization of the poor interfacial electron injection properties exhibited by the dyes when grafted on TiO2 surfaces. Finally, two-photon absorption spectra have been calculated, extremely high cross sections have been obtained in the infrared region paving the way to the possible exploitation of the previous dyes for the development of photoactive smart materials or photodynamic therapy.