Session: Research Posters

Paper Number: 166740

Modulating Optical Properties of 2d Transition Metal Dichalcogenides via Photochromic Molecules: A Computational Approach 

Two-dimensional (2D) transition metal dichalcogenides (TMDs) are a class of materials that have garnered significant attention in the field of optoelectronics due to their remarkable properties. One of the most striking features of TMDs is their ability to transition from an indirect band gap to a direct band gap as they are reduced to monolayer thickness. This transition enhances their suitability for various optical applications, including photodetectors, light-emitting devices, and solar cells. The ability to manipulate their optoelectronic properties opens up exciting possibilities for the development of next-generation optical devices.

In parallel, photochromic molecules present another layer of functionality. These molecules can undergo reversible structural transformations when exposed to ultraviolet (UV) or visible light. Such transformations result in significant changes in their electronic properties, specifically in the energy levels of their highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). The tunability of these energy levels offers a unique opportunity to dynamically control charge transport and exciton behavior in TMDs, which is crucial for enhancing the performance of optoelectronic devices.

This study aims to investigate the feasibility of modulating the optical properties of monolayer TMDs using photochromic molecules through first-principles calculations. Our approach centers on the concept of charge transfer: when the HOMO or LUMO energy levels of the photochromic molecule align with the band gap of the TMD, significant charge transfer can occur. This interaction leads to a depletion of excitons in the monolayer, which are bound states of electrons and holes that play a critical role in the material's optical response.

The isomerization of the photochromic molecule induces a shift in its LUMO (or HOMO) relative to the TMD's conduction band minimum (or valence band maximum). This shift results in a further decrease in electron (or hole) concentrations within the TMD, thereby reducing the exciton population. As a consequence, the overall optical response of the material is diminished. Notably, when the isomerization process is reversed, the original optical properties of the TMD are restored. This reversible mechanism provides a light-responsive switching capability that could be leveraged in various optoelectronic applications.

To identify effective hybrid systems that combine photochromic molecules with TMDs, we conducted density functional theory (DFT) simulations on three prominent monolayers: molybdenum diselenide (MoSe₂), molybdenum disulfide (MoS₂), and tungsten diselenide (WSe₂). Each TMD was coupled with a spiropyran derivative, featuring a C₁₈H₃₇ ligand in both open-chain and closed-chain configurations. By analyzing the density of states, we evaluated energy level shifts and the dynamics of charge transfer within these hybrid structures. Our findings provide crucial insights into the design and optimization of tunable, light-controlled optoelectronic devices based on 2D materials, highlighting the potential of hybrid systems in advancing the field of optoelectronics. This research not only furthers our understanding of TMDs but also paves the way for innovative applications in future technology.

 

Presenting Author: John Audi University of St Thomas

Presenting Author Biography: John Audi is a undergraduate student in the Department of Mechanical Engineering at the University of St Thomas

Authors:

John Audi University of St Thomas
Michael Brophy University of St. Thomas
Jeong Ho You University of St. Thomas
Sewon Park Purdue University
Jong Hyun Choi Purdue University