The Chromic Response to Environment of some Imine-Based Oligomers

Abstract

Among the organic materials widely studied for applications in advanced techniques, imine-based compounds (or azomethines) have received considerable attention due to their ability to reversibly change the color under the action of an external stimulus. The halochromic or photochromic behavior of imines is based on the protonation or photoizomerization ability of the imine linkage, the color changing effect occurring in response to the change in pH of the surrounding medium or electromagnetic radiation absorption. Starting from these aspects, three imine-based oligomers with a donor-acceptor-donor topology containing phenoxazine as the donor unit and diphenyl-1,3,4-oxadiazole, 9,9-diphenylfluorene or fluorene as an acceptor moiety were thoroughly investigated with respect to their protonation and photoiradiation behavior, evaluated by means of photo-physics analysis.

Effect of Protonation on Optical and Electrochemical Properties of Thiophene–Phenylene-Based Schiff Bases with Alkoxy Side Groups

“… 30 − 32 Such a process may lower the glass transition temperature of the doped material, 33 improve its solubility, 33 and increase its conductivity. 33 Moreover, through the change in protonated molecule planarity, 33 the optical 34 , 35 and electrochemical 36 properties are being modified. Protonation of the imine bond may also lead to a major increase in photoluminescence (PL) intensity, 34 , 37 − 39 probably due to the deactivation of photoinduced electron transfer, responsible for the PL quenching in imine compounds.…”

“…Halogen doping is also one of the most often used methods in the case of PAz thin films. , Due to the presence of a lone electron pair connected with a nitrogen atom of the imine bonds, azomethines and PAzs may be also doped using either inorganic or organic acids. − Such a process may lower the glass transition temperature of the doped material, improve its solubility, and increase its conductivity . Moreover, through the change in protonated molecule planarity, the optical , and electrochemical properties are being modified. Protonation of the imine bond may also lead to a major increase in photoluminescence (PL) intensity, ,− probably due to the deactivation of photoinduced electron transfer, responsible for the PL quenching in imine compounds .…”