Date on Senior Honors Thesis

5-2021

Document Type

Senior Honors Thesis

Degree Name

B.S.

Department

Chemistry

Degree Program

College of Arts and Sciences

Author's Keywords

photoswitches,; molecular switches; electric field; computational chemistry; azoheteroarenes; half life

Abstract

Azoheteroarenes are relatively new photoswitchable compounds, where one of the phenyl rings of an azobenzene molecule is replaced by a heteroaromatic five-membered ring. Although few studies have been performed, recent findings on methylated azoheteroarenes show that these photoswitches have great potential in various optically addressable applications. Thermal stability of molecular switches is one of the primary factors considered in the design process. For the purposes of quick information transmission in materials science, the thermal (Z – E) relaxation process should be as short as possible. On the other hand, molecular memory storage devices prefer long Z - E relaxation times. In this computational study, we investigate how oriented external electric fields (OEEFs) can be used to tune the photoswitching properties of three unsubstituted heteroaryl azo compounds – azoimidazole (im), azopyrazole (pz), and azopyrrole (py). (Figure 1) Based on a density functional theory (DFT) approach, we examine the electric field control of the thermal half-lives and nonlinear optical properties of im, pz, and py. We show that favorable OEEF orientations can increase thermal half-life of studied molecules by as much as 60 times, compared to their half-life values in the field-free environment. A deeper understanding of the kinetic and nonlinear optical properties provides greater insight of how molecular switches can be enhanced for user-selective design in different environments.

Lay Summary

Molecular photoswitches are molecules capable of reversible switching with light between two isomers, making them useful for the modification of chemical, physical, and biological properties of materials. Some examples of molecular photoswitch usage are single-molecule optical memories, organic field-effect transistors (OFETs), metal-organic frameworks (MOFs), light-driven molecular crystal actuators, and drug release. One of the factors to consider when constructing a molecular photoswitch is the amount of time the molecule stays in the preferred isomer form. Additionally, it is also important to understand the susceptibility to separate charge in a molecule. In this work, we computationally study the two described factors on three different molecular photoswitches under the application of an external electric field. We show that favorable electric field orientations can increase the switching time of studied molecules by as much as 60 times that of the environment with no field involved. A deeper understanding of these properties can provide greater insight of how molecular switches can be enhanced for user-selective design in different environments.

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