Simple practical method for synthesis of trisubstituted imidazoles: an efficient copper catalyzed multicomponent reaction

A rapid practical process has been developed for synthesis of 2,4,5-trisubstituted-imidazoles in excellent yields up to 95% from readily available starting materials. In this CuI catalyzed synthesis, trisubstituted imidazoles were afforded in short reaction times, wherein the substrate scope is well explored with benzoin as well as benzil reacting with different aldehydes in the presence of ammonium acetate as the nitrogen source.

A rapid practical process has been developed for synthesis of 2,4,5-trisubstituted-imidazoles in excellent yields up to 95% from readily available starting materials.

Solvent polarity dependent excited state hydrogen bond effects and intramolecular double proton transfer mechanism for 2-hydroxyphenyl-substituted benzo[1,2-d:4,5-d']bisimidazole system

In this work, we probe into the photo-induced excited state hydrogen bonding interactions and excited state proton transfer (ESPT) behaviors for a representative benzo[1,2-d:4,5-d']bisimidazole derivative (i.e., 2-hydroxyphenyl-substituted benzo[1,2-d:4,5-d']bisimidazole (HPBB)) compound. In view of aprotic solvents with different polarities, cyclohexane (CYH), dichloromethane (DCM) and acetonitrile (MeCN) solvents are considered. Analyzing hydrogen-bond geometrical parameters, infrared (IR) vibrational spectra, Mayer bond order and predicting hydrogen bonding energy (E_(HB)), we verify dual hydrogen bonds of HPBB are strengthened in S₁ state. Particularly, in nonpolar solvent, the enhanced excited state hydrogen bonds become more obvious. The intriguing charge redistribution and frontier molecular orbitals (MOs) reveal hydrogen bonding acceptance ability of acceptor moieties becomes stronger, which plays a crucial role in capturing hydroxyl proton via photoexcitation. To check and explore ESIPT mechanism, we present the solvent polarity dependent asynchronous excited state intramolecular double proton transfer (ESIDPT) mechanism. That is, nonpolar solvent promotes excited state intramolecular single proton transfer (ESISPT) process for HPBB, while polar solvent contributes to ESIDPT behavior with the primary single proton-transfer product in S₁ state. This work not only makes a rational attribution to experimental phenomena, but also clarifies detailed excited state behaviors for HPBB and presents regulating ESIPT mechanism via solvent polarity.

Biomimetic systems trigger a benzothiazole based molecular switch to 'turn on' fluorescence

Molecular switches are valuable tools for the detection of many chemical and biological processes. On the other hand, Schiff bases are known for their simplicity in synthesis and their enormous biochemical applications. In this scenario, when a strategically designed Schiff base acts as a molecular switch in biomimetic environments drags inevitable attention. In this article, we hereby demonstrate an interesting behavior of a strategically designed bioactive benzothiazole based Schiff base (E)-2-(((6-chlorobenzo[d]thiazol-2-ylimino)methyl)-5-diethylamino) phenol (CBMDP) whose fluorescence characteristics dramatically modulate as consequence of its structural modification in aqueous and biomimetic environments individually. Electronic absorption, steady state and time resolved fluorescence spectroscopic techniques along with DFT based quantum chemical calculation evidence that in pure organic solvents CBMDP exists in highly fluorescent enol-imine (N) form which transform into feebly fluorescent hydrated species (H) in bulk aqueous media. Contrariwise, on interaction with the ionic and non-ionic micellar media or with liposome, a structural restoration occurs from less fluorescent hydrated (H) species into a highly fluorescent normal (N) one. This molecular flipping of the title compound upon micellar compartmentalization is possibly caused by the micropolarity of the local environment and further supported by its spectral behavior in different polarity gradient solvent mixture of water-dioxane (protic-aprotic) and water-methanol (protic -protic). Usually, Schiff bases are prone to hydrolysis in aqueous media, interestingly, the structural framework of this strategically designed molecule only allow the first step of hydrolysis, which is hydration of azomethine linkage whereas it withstand the second step, and that possibly helps the structural restoration process. Hence the article described herein may emphasize how a systematically designed Schiff base framework can be used as 'turn off- turn on' fluorescent molecular switch which may be extremely useful for its applications in the area of biochemical sensors.

Modulation of Excited State Proton Transfer Dynamics of a Lactim-Lactam Tautomeric System in Different Block Copolymer-Surfactant Aggregates

The proton transfer (PT) process in 1-(2-hydroxy-5-chloro-phenyl)-3,5-dioxo-1H-imidazo-[3,4-b]isoindole (ADCL) has been studied in three different copolymer-surfactant supramolecular assemblies prepared in aqueous 1% P123 triblock copolymer micellar solution with varying concentrations of surfactants (sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and triton-X-100 (TX 100)). The aim of the present study is to monitor the modulation of the PT process by changing the degree of micellar hydration inside the P123 micelle with the addition of the three different surfactants (two ionic and one non ionic), that is, in P123-surfactant aggregates. Besides, a comparative study has been done with these results with those in water, pure P123 micellar medium and three different surfactants medium. The micropolarity measurement and time-resolved fluorescence anisotropic measurements have been performed to evaluate the binding location of the probe (ADCL) in the three different copolymer-surfactant supramolecular assemblies. It is found that the micropolarity at the binding site of the molecule in the various environments largely influences the PT rate of ADCL. The PT rate is found to be the slowest in the P123 medium and in P123-surfactant aggregates the rate becomes faster as the micropolarity around the binding locations of the molecule in these aggregates is higher in comparison to that in P123 micelle.