Quantum chemical calculations and experimental studies of third-order nonlinear optical properties of conjugated TTF–quinones

• Static and dynamic (α), (γ  ) and also dynamic (χ(3))(χ(3)) using TDHF method for 1 and 2 are calculated.
• OPA characterizations and HOMO, LUMO, HOMO–LUMO gaps are evaluated by CI and DFT methods, respectively.
• Compounds 1 and 2 might possess third-order NLO phenomena.
• Theoretical results for susceptibilities explain the experimental findings.

To investigate microscopic third-order nonlinear optical (NLO) behaviour of two tetrathiafulvalene (TTF) derivatives, TTF–diquinone triad (1) and TTF–monoquinone dyad (2), we have computed both dispersion-free and also dispersion of dipole polarizabilities (α) and third-order hyperpolarizabilities (γ) at 532 nm wavelength using time-dependent Hartree–Fock (TDHF) method. The one-photon absorption (OPA) characterizations of the title molecules have been theoretically obtained by means of configuration interaction (CI) method with all doubly occupied molecular orbitals. We have also calculated the dynamic third-order susceptibilities (χ(3)) using the TDHF method. Our theoretical results on the maximum OPA wavelengths, third-order susceptibilities and corresponding microscopic NLO responses are in good agreement with the previous experimental observations of the examined TTF-based molecules. The highest occupied molecular orbitals (HOMO), the lowest unoccupied molecular orbitals (LUMO) and the HOMO–LUMO band gaps for 1 and 2 have been evaluated by density functional theory (DFT) quantum mechanical calculations at B3LYP/6–31G(d, p) level.

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