Experimental and Theoretical Investigation of Excited-State Intramolecular Proton Transfer Processes of Benzothiazole Derivatives in Amino-polydimethylsiloxanes before and after Cross-Linking by CO 2

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2020-01, Vol.124 (2), p.288-299
• Main Authors: T A Duarte, Luís Gustavo, Rodembusch, Fabiano S, Atvars, Teresa D Z, Weiss, Richard G
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.9b10325

The changes in the ability of three fluorescent derivatives of 2-(2'-hydroxyphenyl)benzothiazole to undergo excited-state intramolecular proton transfer (ESIPT) processes have been correlated with the rheological properties of four amino-polydimethylsiloxanes with different molar masses and containing different amounts of monomer units with amino pendant groups, in the presence and absence of a cross-linking molecule, CO . The changes lead to a variety of species (keto, enol, and enolate forms) in both the ground and excited states. Calculations using the density-functional theory/time-dependent density-functional theory method at the CAM-B3LYP/6-311++G(d,p) level helped to identify how ESIPT is involved in the formation of the intermediates. The results demonstrate that proton transfer in 2-(2'-hydroxyphenyl)benzothiazoles is a powerful tool to identify local changes in the viscosity and micropolarity of the environment that are attributed to the structural differences of the amino-polydimethylsiloxanes and their cross-linking.