Synthesis, electrochemical, thermal and photophysical characterization of photoactive discotic dyes based on the tris-[1,2,4]-triazolo-[1,3,5]-triazine core

Abstract

This work presents the synthesis and characterization of compounds based on the heterocycle tris-[1,2,4]-triazolo-[1,3,5]-triazine (TTT) obtained by a new building block that can be applied to afford different discotic materials in one step. The thermal properties were evaluated by TGA and DSC and indicate very thermal stable compounds. The compounds exhibited absorption in the UV-B region (∼280 nm) with molar absorptivity coefficients and radiative rate constants arising from spin and symmetry allowed π–π* electronic transitions. An emission located in the UV-A region (∼363 nm) was observed, which was most likely due to a normal emission because no evidence of a charge-transfer mechanism in the excited state was observed. Spin-coated films indicate the presence of π-stacking in compounds presenting lower alkyl chains. Cyclic voltammetry measurements showed reduction and oxidation processes. The HOMO energy was obtained from the oxidation potential corresponding and the LUMO energy was found by subtracting its optical band gap from the HOMO value. In addition, in situ UV-Vis measurements were employed to evaluate the changes in the absorption spectra due to the changes in the electronic structure of the conjugated molecules under oxidative and reductive potentials.