Electrical and optical properties of thermally-evaporated thin films from A2[TiO(C2O4)2] (A = K, PPh4) and 1,8-dihydroxyanthraquinone

In this work, the synthesis of molecular materials formed from A2[TiO(C2O4)2] (A = K, PPh4) and 1,8 dihydroxyanthraquinone is reported. The synthesized materials were characterized by atomic force microscopy (AFM), infrared (IR) and ultraviolet-visible (UV-vis) spectroscopy. IR spectroscopy showed that the molecular-material thin-films, deposited by vacuum thermal evaporation, exhibit the same intra-molecular vibration modes as the starting powders, which suggests that the thermal evaporation process does not alter the initial chemical structures. Electrical transport properties were studied by dc conductivity measurements. The electrical activation energies of the complexes, which were in the range of 0.003-1.16 eV, were calculated from Arrhenius plots. Optical absorption studies in the wavelength range of 190-1090 nm at room temperature showed that the optical band gaps of the thin films were around 1.9-2.3 eV for direct transitions Egd. The cubic NLO effects were substantially enhanced for materials synthesized from K2[TiO(C2O4)2], where χ(3) (−3ω; ω, ω, ω) values in the promising range of 10−12 esu have been evaluated.

Research highlights▶ Synthesis of molecular materials formed from A2[TiO(C2O4)2] (A = K, PPh4) and 1,8 dihydroxyanthraquinone. ▶ Thin films show electrical conductivities of the order of 10−5 Scm−1. ▶ Optical studies showed that the optical band gaps of the thin films were around 1.9−2.3 eV. ▶ The measurement of cubic-only, non-degenerated χ (3) (−3ω; ω, ω, ω) NLO coefficients in all the studied samples, instead of quadratic- χ (2) ones, pointed out to predominantly amorphous structured-molecular arrangements.