Synthesis and study of the photophysical properties of tetrazole-based push-pull chromophores

Abstract

Push-pull chromophores (also, called donor-acceptor compounds) are delocalized π-electron systems with a donor at one end of the molecule and an acceptor at the other. These compounds are used as active materials in organic devices such as organic light emitting diodes (OLED), organic photovoltaic cells (OPVC) and dye-sensitizing solar cells (DSSC). There are numerous studies on heterocyclic push-pull compounds based on oxazoles, oxadiazoles and triazoles with promising optical and photophysical properties. However, systematic study of the substituent effect on the photophysical properties of tetrazole-based donor-acceptor compounds is scarce in the literature. Thus, the aim of this project was to synthesize several push-pull tetrazole compounds of the general structure 2,5-AD and 2,5-DA with varying strengths of donors (D) and acceptors (A) and investigate their photophysical properties by UV-Vis and fluorescence spectroscopy. The key step in the synthesis of 2,5-AD and 2,5-DA involved a copper-catalyzed aerobic C-N coupling reaction of the appropriately substituted aryl tetrazoles and aryl boronic acids. The photophysical properties were analyzed in different organic solvents, using ultra-violet visible and fluorescence spectroscopy. Our work so far shows that the UV-Vis absorption characteristics of these molecules can be tuned with substituents. The 2,5-AD compounds studied showed weak emission, while no fluorescence was observed from the 2,5-DA compounds. Our preliminary work indicates that the synthesized compounds exhibit small solvatochromic behavior and cannot serve as solvent polarity indicators.