Differential Behavior of Amino-Imino Constitutional Isomers in Nonlinear Optical Processes

• Published in: Chemphyschem Vol. 11; no. 4; pp. 912 - 919
• Main Authors: Latorre, Sonia, Moreira, Ibério de P. R., Villacampa, Belén, Julià, Lluís, Velasco, Dolores, Bofill, Josep Maria, López-Calahorra, Francisco
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 15-03-2010; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc
• Subjects: Ab initio calculations; Atomic and molecular physics; Calculations and mathematical techniques in atomic and molecular physics (excluding electron correlation calculations); Electronic structure of atoms, molecules and their ions: theory; Exact sciences and technology; heterocyclic compounds; nonlinear optics; Physics; tautomerism; valence-bond model; Aromatics; tautomerism; Nitrogen heterocycle; Acridine derivatives; Optical properties; Theoretical study; Ab initio calculations; heterocyclic compounds; Isomers; Nonlinear optics; valence-bond model; Organic compounds
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.200900616

A detailed study of the “blocked” amino–imino tautomers derived from N‐acridine‐substituted 2‐aminobenzothiazole—and their effect on the nonlinear optical response—is presented. The synthesis, characterization, and nonlinear optical properties of these frozen tautomers, namely, N‐methyl‐N‐(2‐nitroacridin‐6‐yl)‐2‐aminobenzothia‐zole and 3‐methyl‐N‐(7‐nitroacridin‐3‐yl)‐2‐iminobenzothiazole, are reported. A theoretical model based on valence–bond theory is also proposed and used to analyze the effects of the nuclear configuration corresponding to each frozen tautomer structure. In the present case, the aromatic form and the allylic‐anion‐like system of the NCN group inherent to each isomer are crucial for understanding and analyzing the different responses of each “blocked” tautomer.
Differential behavior of tautomers: Small changes between 2‐amino and 2‐iminobenzothiazol isomers induce significant differences in their electronic structure and properties. This behavior leads to electronic effects that are essential for understanding the nonlinear optical response of these heterocyclic chromophores (see picture) and is also expected to be relevant in other analogous π systems.