A Quantum Mechanical Description of Photosensitization in Photodynamic Therapy using a Two-Electron Molecule Approximation

TL;DR

This paper presents a quantum mechanical model of photosensitization in photodynamic therapy, approximating the involved molecules as two-electron systems and detailing the energy transfer process.

Contribution

It introduces a novel quantum mechanical framework for understanding photosensitization in PDT using a two-electron molecule approximation.

Findings

Conservation laws are maintained throughout the process.

The model describes energy transfer via intersystem crossing and electron exchange.

Provides a fundamental quantum description applicable to medical and educational contexts.

Abstract

A fundamental, Quantum Mechanical description of photoactivation of a generic photosensitizer and the ensuing transfer of energy to endogenous oxygen as part of the Type II pathway to photodamage during photodynamic therapy (PDT) is presented. The PS and molecular oxygen are approximated as two-electron molecules. Conservation of energy and of angular momenta of the two molecule system are abided via selection rules throughout the four-stage process, including initial states, absorption of a photon by the PS, conversion of the PS to an excited spin triplet via intersystem crossing (ISC), and the transition of molecular oxygen to an excited spin singlet state via a Triplet-Triplet Exchange of electrons with the PS. The provided description of photosensitization will provide students and researchers with a fundamental introduction to PDT, while offering the broader population of Quantum Mechanics and Physical Chemistry students an advanced example of quantum systems in an applied, medical context.