Examination of photophysical characteristics of perylene diimide chromophores and their potential application in electro-optical technologies

Abstract

1,6-, 1,7-, and 1,6,7- derivatives of dodecylthio–N,N’– (2,4–diisopropylphenyl)-3,4,9,10-perylenetetracarboxylic diimide, and N,N’-Di(4-ethynylphenyl)-1,7-di(4-tert-butylphenoxy)-3,4:9,10-perylenebis-(dicarboximide) (PhO-Ph-PDI) were synthesized, isolated, and characterized. The three Thio-PDI derivatives, 1,6–Thio–PDI, 1,7–Thio–PDI, and 1,6,7–Thio–PDI, displayed noticeable differences in their photophysical properties including their absorption and emission spectra, fluorescence quantum yield, fluorescence excited state lifetimes, and excited state dipole moments as calculated by the Lippert-Mataga analysis. Additionally, the Thio-PDI derivatives exhibited different colors at neutral and reduced state as determined by chemical reduction and CIE calculations. These studies determine that different PDI derivatives can provide unique photophysical contributions as building blocks within the molecular assemblies which comprise new technologies such as electrochromic (EC) devices. Comparatively, PhO-Ph-PDI was utilized as the primary building block within a molecular assembly for potential use in EC materials. A molecular assembly, or thin-film, of PhO-Ph-PDI was fabricated Copper Azide-Alkyne Cycloaddition reactions. The PhO-Ph-PDI thin-film was studied with TBAPF6 and TMeAPF6 in various solvents to study electrolyte size penetration within the PhO-Ph-PDI thin-film. Different reduced states were probed with cyclic voltammetry studies, spectroelectrochemical studies, and potential step spectroelectrochemical studies. These studies revealed that a combination of a smaller TMeAPF6 electrolyte and a longer applied potential allowed for better cation penetration through the PhO-Ph-PDI thin-film. This better penetration of the thin-film led to higher conversion of reduced states which is an essential criteria of EC devices. While the PhO-Ph-PDI thin-film did not achieve full conversion to all reduced states with either electrolyte, analysis of the PhO-Ph-PDI thin-film provides better understanding of the criteria required to improve molecular assemblies for EC devices. This includes selection of appropriate sized electrolyte and synthetic design of molecular assembly channel size by appropriate selection of chromophores utilized within the molecular assembly.