Investigation of Mechanisms of Reversible Photodegradation of 1-Amino-2-Methylanthraquinone Doped in PMMA Polymer Using Semi-Empirical Potential Energy Surface Calculations

The mechanisms of reversible photodegradation of 1-amino-2-methylanthraquinone in PMMA have previously been studied through the use of amplified spontaneous emission (ASE) and linear absorption spectroscopy. From this, and other work on related anthraquinone species, the commonly accepted mechanism of reversible photodegradation is a phototautomerization in which a proton from the amine is transferred to the adjacent oxygen. Though this work has provided invaluable information, it alone is unable to extricate a complete answer as to the mechanisms of degradation and recovery. Herein the potential energy surface (PES) of the phototautomerization reaction for 1-amino-2-methylanthraquinone is analyzed using MO semi-empirical potential energy surface calculations, revealing it to be an unlikely mechanism. Additionally an alternate theoretical mechanism in which the generation of a long lived twisted intramolecular charge transfer (TICT) state is responsible for reversible photodegradation is looked at in brief.