Photophysical Behavior of Malachite Green in Solid and Liquid Media

Abstract

Malachite Green (MG) incorporated in glass appears in four forms. In acidic glasses, yellow H(MG)²⁺ protonated dications; the green monocation MG⁺ in H₂O at pH 4 to 6; the colorless carbinol base HO(MG) at higher pH; and a new purple species in certain glasses prepared by mineral acid catalysis. Uniquely high luminescence yields indicate formation of chemical bonds between MG⁺ and the silicate groups, suggesting Lewis-acid behavior of three-coordinated carbon. Novel cascade emission is observed from the three first excited singlets S₁ S_2, and S_3- In sol-gel glasses, green MG⁺ bleaches reversibly under illumination.