Acid-responsive behavior promoted by imine units in novel triphenylamine-based oligomers functionalized with chromophoric moieties

Abstract

A series of oligomeric poly(ether-imine)s, named by us oligo(ether-imine)s were synthesized by polycondensation reaction of some di(ether-aldehyde)s with a CF3-substituted and ortho-catenated triphenylamine (TPA) diamine. The obtained TPA-based oligomers with ortho-link structural pattern, not encountered yet for this class of compounds, displayed excellent organosolubility in the majority convenient and accessible solvents. This enabled their easy processing in homogenous thin film with granular or vesicular morphology, another novel feature highlighted for this class of compounds. The photo-optical activity of oligo(ether-imine)s was investigated in detail by UV–vis and fluorescence spectroscopy, which evidenced the occurrence of a dual intramolecular charge transfer between TPA and both CF3 units and imine-phenyl framework. The acid sensing properties were surveyed both in solution and solid state, being found that upon protonation the planarity is lessen, the donor-acceptor strength decreases and the ICT bands are hipsochromically shifted. Instead, due to pH-induced conformational changes of the present molecules, the quenched fluorescence of the neutral states was turned-on. The redox behavior measured by cyclic voltammetry before and after protonation was contingent on the type of chromophoric unit incorporated into the dialdehyde segment. Owing to their ability to promote favorable, multifunctional properties, applications of these oligomers in optoelectronic devices or pH-sensors are foreseen.