Nitro-Substituted 4-[(Phenylmethylene)imino]phenolates: Solvatochromism and Their Use as Solvatochromic Switches and as Probes for the Investigation of Preferential Solvation in Solvent Mixtures

Abstract

Four 4-[[(4-nitrophenyl)methylene]imino]phenols (2a-d) were synthesized. After deprotonation in solution, they formed the solvatochromic phenolates 3a-d, which revealed a reversal in solvatochromism. Their UV-vis spectroscopic behavior was explained on the basis of the interaction of the dyes with the medium through combined effects, such as nonspecific solute-solvent interactions and hydrogen bonding between the solvents and the nitro and phenolate groups. Dyes 3a-c were used as probes to investigate binary solvent mixtures, and the synergistic behavior observed was attributed to solvent-solvent and solute-solvent interactions. A very unusual UV-vis spectroscopic behavior occurred with dye 3d, which has in its molecular structure two nitro substituents as acceptor groups and two phenyl groups on the phenolate moiety. In alcohol/water mixtures, the E(T)(3d) values increase from pure alcohol (methanol, ethanol, and propan-2-ol) until the addition of up to 80-96% water. Subsequently, the addition of a small amount of water causes a very sharp reduction in the E(T)(3d) value (for methanol, this corresponds to a bathochromic shift from 543 to 732 nm). This represents the first example of a solvatochromic switch triggered by a subtle change in the polarity of the medium, the color of the solutions being easily reversed by adding small amounts of the required cosolvent.

Negative Solvatochromism of an Anionic Thiazole‐Based Dye

“…Selected UV/vis spectra of compound 2 are shown in Figure 2. The longest‐wavelength absorption can be attributed to a strong π–π* transition from the S 0 to the S 1 state with an intramolecular charge transfer (ICT) character that is typical for these push‐pull dyes 10. The λ max of the absorption varies from 510 nm for the polar strong HBD solvent methanol to 624 nm for the very polar solvent tetramethylurea (TMU), which results in a negative solvatochromism of 114 nm (3580 cm −1 or 0.44 eV).…”

“…Recently, an extended anionic nitrophenol derivative was presented by Nandi et al. in 2012 10. Unfortunately, the dye was not described fully as it was generated in situ and its properties measured directly.…”

An Azo Dye Based D‐π‐A Chromogenic Probe for Selective Naked‐Eye Detection of Hg2+ Ion: Application in Logic Gate Operation

“…Due to the existence of D‐π‐A unit, upon excitation, the chromophore experiences a large change in dipole moment as a result of change in the relative contributions from different resonating structures i. e. less polar benzenoid form and more polar quinonoid form. Suitably substituted azo dyes forming D‐π‐A framework are proved to be a preferred probe for monitoring micro polarity, specific solute‐solvent interactions, complex biochemical and biological interactions due to their greater sensitivity towards environmental changes . Recently, we have utilized an azo dye 4‐ ( p ‐nitrophenylazo) phenol with a donor‐ π‐acceptor (D‐π‐A) framework as a solvatochromic probe to study solute‐solvent intermolecular interactions in pure and binary mixture of solvents.…”

The Colorimetric Signaling of Water Content by a Deprotonated Schiff Base in some Aprotic Organic Solvents

“…This will give more accurate results for water signaling because it will not depend on the anion concentration. Besides, the deprotonated form of few dyes shows colorimetric solvatochromism …”