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 S2, and S3- In sol-gel glasses, green MG+ bleaches reversibly under illumination.