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Photochromism

Overview

Photochromism is the reversible transformation of a molecule between two distinct forms upon irradiation with light of appropriate wavelengths. The two forms generally differ in their molecular structure, absorption spectrum, and physicochemical properties. This phenomenon forms the basis of molecular switches, optical memories, smart materials, and photosensitive devices.

The photochromic conversion usually proceeds through excited electronic states, followed by structural rearrangements such as bond cleavage, bond formation, or isomerization.

Computational Studies

Computational chemistry provides molecular-level insight into photochromic processes that are often inaccessible experimentally. Electronic structure methods and excited-state calculations help determine

  • Ground- and excited-state potential energy surfaces
  • Absorption and emission spectra
  • Conical intersections governing ultrafast relaxation
  • Reaction pathways between photochromic states
  • Energy barriers for thermal back reactions

Methods commonly employed include Density Functional Theory (DFT), Time-Dependent DFT (TD-DFT), CASSCF, CASPT2, and nonadiabatic molecular dynamics.

Computational investigations enable the rational design of efficient photochromic materials with improved fatigue resistance, switching efficiency, and optical performance.