Solvato-, thermo- and photochromism in a new diazo diaromatic dye:2-(p-tolyldiazenyl)naphthalen-1-amine

The novel azo dye 2-(p-tolyldiazenyl)naphthalen-1-amine (2tona) was synthesized and structurally characterized by infrared, H-1-and C-13 NMR spectroscopies, complemented by density functional theory (DFT) calculations on the different possible isomeric species of the compound. The solvatochromism exhibited by 2tona in several solvents with different characteristics, as well as its thermo-and photochromic properties, were then investigated using UV-vis absorption spectroscopy, complemented by time-dependent DFT calculations.Solvatochromism was evaluated using the Kamlet-Taft model, highlighting the relevance of dipolar-ity/polarizability of the solvent, but also of its hydrogen bonding acceptor and donor abilities, in deter-mining the optical properties of 2tona in the different solutions studied. In apolar solvents and polar sol-vents with no ability to participate in H-bonds as donors, the solutions show yellow tones, and only the azo-trans isomeric form of the compound exists (two conformers in equilibrium). Solvents with higher polarity and H-bond acceptor character red shift the bands of the azo-trans conformers observed in the visible region, with all probability by stabilizing their LUMO and LUMO + 1 orbitals. The red tones of the solutions of the solvents with high ability to participate in H-bonds as donors reveal the presence in these media also of the hydrazone-trans tautomer of the compound.Thermo-and phochromic (induced by UV light; lambda = 311 nm) behaviors observed in methanol and chloroform solutions were also evaluated, and interpreted in terms of azo-hydrazone tautomerism and cis -trans isomerism.The studied compound appears as a versatile solvato-, thermo-and photochromic system, which is sensitive to different types of intermolecular interactions with the solvent, thus being a good candidate for practical applications in materials sciences. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

The novel azo dye 2tona displayed solvatochromism in different solvents and showed thermo-and photochromic properties. The compound appears to be a versatile system sensitive to different types of intermolecular interactions with the solvent.