Structural and electrochemical studies of TiO2 complexes with (4,4′-((1E,1′E)-(2,5-bis(octyloxy)-1,4-phenylene)bis(ethene-2,1-diyl))bis-(E)-N-(2,5-bis(octyloxy)benzylidene)) imine derivative bases towards organic devices

Abstract

Three (4,4′-((1E,1′E)-(2,5-bis(octyloxy)-1,4-phenylene)bis(ethene-2,1-diyl))bis-(E)-N-(2,5-bis(octyloxy)benzylidene)) imine derivatives were synthesized via a condensation reaction with p-toluenesulfonic acid as a catalyst. The effects of the end groups and vinylene (–HCCH–) moieties on the structural, thermal, optical, electrochemical and photovoltaic properties of imines were investigated to check the influence of TiO₂ on the imine properties. The thermal behavior of imines and their complexes with TiO₂ was widely investigated using FT-IR, XRD, DSC and POM methods in order to determine the order type in the imine structure. All imines present the highest occupied molecular orbital (HOMO) levels of about −5.39 eV (SAI1 and SAI2) and −5.27 eV (SAI3) and the lowest unoccupied molecular orbital (LUMO) levels at about −3.17 eV. The difference of the end groups in the imines in each case did not affect redox properties. Generally, both oxidation and reduction are easier after TiO₂ addition and it also changes the HOMO–LUMO levels of imines. Moreover, changes in the characteristic bands for imines in the region 1500–1700 cm⁻¹ observed as a drastic decrease of intensity or even disappearance of bands in the imine : TiO₂ mixture suggest the formation of a complex (CN)–TiO₂. Organic devices with the configuration of ITO/TiO₂/SAIx (or SAIx : TiO₂)/Au were fabricated and investigated in the presence and absence of visible light irradiation with an intensity of 93 mW cm⁻². In all imines and complexes with TiO₂, the generation of the photocurrent indicates their use as photodiodes and the best result was observed for SAI3 : TiO₂ complexes.