Two-photon circular-linear dichroism of perylene in solution: a theoretical-experimental study.

Herein, we report on the theoretical-experimental analysis of the two-photon absorption (TPA) and two-photon circular-linear dichroism (TPCLD) spectra of a highly conjugated, rigid, and centrosymmetric molecule in solution, that is, perylene/CH2Cl2. We show how a three-energy-level diagram, under the sum-over-essential states approach, assists in the determination of the magnitude of transition electric dipole moments and the angle between them for the main TPA transitions. We demonstrate the potential of TPCLD to reveal the symmetry of excited states and the angles between their transition electric dipole moments and that of the ground state. By means of TPCLD, we explain how the overwhelming contribution of certain TPA transitions can mask important spectral features in regions where the transition electric dipole moments are perpendicular. TPCLD is expected to enhance the understanding of the photophysical properties of materials that are not accessible using conventional linear and two-photon spectroscopy. TPA and TPCLD measurements were performed employing the open-aperture Z-scan technique using an amplified femtosecond system. Time-dependent density functional theory (TD-DFT) calculations were carried out using response theory at the B3LYP level with the aug-cc-pVDZ basis set. Solvent effects were included through the polarizable continuum model (PCM).