Comprehensive study on excited state intramolecular proton transfer in 2-(benzo[d]thiazol-2-yl)-3-methoxynaphthalen-1-ol and 2-(benzo[d]thiazol-2-yl)naphthalene-1,3-diol: Effect of solvent, aggregation, viscosity and TDDFT study

An insight into the dual fluorescence of 3,6-dihydroxybenzene-1,2,4,5-tetracarboxylic acid tetraethyl ester - An experimental and theoretical study

The Excited State Intramolecular Proton Transfer (ESIPT) phenomenon involving photo-induced keto-enol tautomerization is known to cause significant variations in the excited state structures and photophysical properties of certain molecules. Here, the dual emission exhibited by 3,6-dihydroxybenzene-1,2,4,5-tetracarboxylic acid tetraethyl ester has been studied both experimentally and theoretically and it is concluded that the second emission is due to ESIPT in polar protic solvents, while it is due to dianion formation in solvents like DMSO and DMF.

Revelation solvent effects: excited state hydrogen bond and proton transfer of 2-(benzo[d]thiazol-2-yl)-3-methoxynaphthalen-1-ol

ESIPT reaction of an MMT molecule is gradually inhibited with increasing solvent polarity.

Fluorescence light-up detection of cyanide in water based on cyclization reaction followed by ESIPT and AIEE

Schiff base 1 (2,4-di-tert-butyl-6-((2-hydroxyphenyl-imino)-methyl)phenol) containing two hydroxyl groups could undergo an oxidative cyclization reaction and then generate hydroxyphenylbenzoxazole (HBO) 2 when CN^- was present as a catalyst. The multistep cyclization reaction was proved by spectroscopy, ¹H NMR, ¹³C NMR and mass spectra. C[double bond, length as m-dash]N isomerization is the predominant decay process of the excited states, so sensor 1 is weakly emissive in solution at ambient temperature. When 1 reacts with CN^-, the emission is remarkably enhanced, where 1 is converted to 2. The cyclization product HBO 2 displays bright green luminescence in micellar due to the ESIPT (excited-state intramolecular proton transfer) as well as AIEE (aggregation-induced emission enhancement) effect. The detection limit is 5.92 × 10^-7 M, lower than the WHO guideline of CN^- in drinking water (1.9 μM). The selective and competitive experiments reveal that sensor 1 shows high sensing selectivity and sensitivity for CN^- over other anions. Test papers containing absorbed 1 were prepared and applied for practical application of cyanide detection.

Photoinduced Electron Transfer Switching Mechanism of a Naphthalimide Derivative with its Solvatochromic Behaviour: An Experimental and Theoretical Study with In Cell Investigations

The sole existence of a t-bone-shaped naphthalimide derivative [2-(2-aminoethyl)-1H-benzo[de]isoquinoline-1,3(2H)dione] (NAP), which gives rise to a photoinduced electron transfer (PET) mechanism, has been established using a combination of experimental and theoretical studies. In parallel an in vitro-in cell PET mechanism has also been shown. To understand the photophysics of NAP, solvent studies have been carried out in different solvents. In addition, theoretical calculations have been conducted to explain the spectroscopic properties through optimized structures. A "turn off" PET mechanism has also been observed in the presence of specific metal ions, namely, Cr³⁺ , Fe³⁺ and Hg²⁺ among a series of metal ions. Theoretical studies reveal that NAP-Cr³⁺ , NAP-Fe³⁺ and NAP-Hg²⁺ have their HOMO energy states lying in between a HOMO-LUMO energy state of the t-bone-type NAP molecule. On the contrary, the HOMO state of the other metal ion-NAP conjugate (NAP-Mⁿ⁺ ) does not lie in between the HOMO-LUMO energy gap of the t-bone-type NAP molecule. Coupled with in vitro studies, in cell investigations reveal an enhancement of fluorescence intensity of NAP upon cytosolic metal sensing. Furthermore, a very high cell viability of NAP treated cells as tested by MTT assay and a fast permeation of the said compound as revealed by flow cytometry suggest NAP to be a potential candidate in metal sensing and bioimaging applications.