Preference for excited state imine-amine isomerisation over enol-keto isomerisation: spectroscopic exploration and quantum chemical calculations.

In this article, the photophysical properties of ethyl-3-(benzo[D]thiazol-2-yl)-5-chloro-2-hydroxybenzoate (EBTCH) and ethyl-3-(benzo[D]oxazol-2-yl)-5-chloro-2-hydroxybenzoate (EBOCH) have been explored spectroscopically along with quantum chemical calculations. From a structural viewpoint, both molecules have two proton acceptor sites (thiazole/oxazole N atom and ester O atom) and a common proton donor site (phenolic -OH) connected by a six-membered H-bonding ring capable of both imine-amine and enol-keto photoisomerisation. Steady state absorption and emission spectra and time-resolved fluorescence characteristics of EBTCH and EBOCH and a comparison with the spectral data of controlled compounds 2-(benzo[D]thiazol-2-yl)-4-chlorophenol (BTCP), 2-(benzo[D]oxazol-2-yl)-4-chlorophenol (BOCP) and ethyl 5-chloro-2-hydroxybenzoate (ECHB) support the preference for imine-amine isomerisation over enol-keto isomerization in the excited state.

Storehouse of Peculiar Supramolecular Architecture: Probing the Charge-Transfer Phenomenon and Effect of Altering the pH in a Meta-Oriented Single Donor-Double Acceptor Fluorophore.

The investigation of excited-state intramolecular charge transfer (ESICT) has been a fascinating area of research. Although the ESICT events have been studied mostly for -disubstituted donor-acceptor type molecules, the -oriented donor-acceptor type molecules have also shown tremendous potential as ESICT active molecules. In the current work, a small fluorescent probe diethyl 5-amino isophthalate () was investigated as a potential model to investigate ESICT events in the solution as well as solid phase.

Switching of photoinduced proton transfer from one six-membered hydrogen-bonded ring to other: a molecule of hydrazine and pH sensor.

The present study describes photophysical properties of 3-(benzo[]oxazol-2-yl)-5-bromo-2-hydroxybenzaldehyde (HBOB) and ()-2-(benzo[]oxazol-2-yl)-4-bromo-6-(hydrazonomethyl)phenol (HBON) molecules with asymmetric two-way proton transfer sites. The purpose of this study is to know the direction of ESIPT out of the two-way proton transfer pathways in these molecules in both the solid and solution state. The steady state and time-resolved spectral behaviour of HBOB and HBON and a comparison of the spectral features with the two distinct control compounds 2-(benzo[]oxazol-2-yl)-4-bromophenol (HBO) and ()-4-bromo-2-(hydrazonomethyl)phenol (HBN) having single 6-membered hydrogen bonded network reveal that HBOB undergoes imine-amine photoisomerisation by proton transfer towards the oxazole side and HBON undergoes towards the hydrazone side with characteristic Stokes' shifted emission.

Investigating the Photophysical Aspects of a Naphthalene-Based Excited-State Proton Transfer Dye 1-(1-Benzo[]imidazol-2-yl)naphthalen-2-ol: pH-Dependent Modulation of Photodynamics.

The steady state and time-resolved photophysical behavior of a proton transfer dye 1-(1-benzo[]imidazol-2-yl)naphthalen-2-ol () was investigated. The excited state intramolecular proton transfer (ESIPT) reaction in is predominant in nonpolar solutions (toluene and DCM) with a lifetime of ∼1.0 ns.

Dual-Channel Imine-Amine Photoisomerization in a Benzoimidazole and Benzothiazole Coupled System: Photophysics and Applications.

A molecule, namely 2-(1-benzo[]imidazol-2-yl)-6-(benzo[]thiazol-2-yl)-4-bromophenol (), having a two-way proton transfer unit of thiazole and imidazole moieties was synthesized and characterized by NMR, electrospray ionization mass spectrometry (ESI-MS), and single-crystal diffraction studies. Steady state and time-resolved spectral studies of support excited state intramolecular proton transfer (ESIPT), causing imine-amine tautomerization through a two-way 6-membered H-bonded ring, where the N atoms of benzothiazole and the benzoimidazole unit are involved as proton acceptor sites. Interestingly, in a nonpolar and moderately polar solvent, photoisomerization in is found to be favored toward the thiazole ring, whereas in a highly polar solvent, it is favored toward the imidazole ring.

Interrogating the nature of aggregates formed in a model azine based ESIPT coupled AIE active probe: stark differences in photodynamics in the solid state and aggregates in water.

A novel Schiff base 4-bromo-2-(()-(()-(1-(naphthalen-2-yl)ethylidene)hydrazono)methyl)phenol (BNHMP) was synthesized and characterized by NMR, ESI-MS, FTIR and single crystal X-ray diffraction studies. In the solution phase, BNHMP shows prominent emission from the keto-form, a consequence of excited state intramolecular proton transfer (ESIPT). The quantum yield and excited state lifetime decrease in polar solvent THF compared to relatively non-polar solvent DCM.

Structural isomerism induces pH dependent AIE-coupled ESIPT: an in-depth spectroscopic exploration with application in amine vapor sensing.

A novel excited state intramolecular proton transfer probe 3-(benzo[]thiazol-2-yl)-4-hydroxy-5-methoxybenzaldehyde (3BTHMB) was synthesized and characterized using NMR, ESIMS and single crystal diffraction studies. The steady state and time resolved studies using the time correlated single photon counting (TCSPC) technique revealed that 3BTHMB shows ESIPT reaction with a time constant of 0.10-0.

Fluorescence detection of Al ion in aqueous medium and live cell imaging by ESIPT probe (E)-N'-(5-bromo-2-hydroxybenzylidene)-4-hydroxybenzohydrazide.

The molecule (E)-N'-(5-bromo-2-hydroxybenzylidene)-4-hydroxybenzohydrazide (BHHB) has been synthesized and its photophysical properties have been investigated by using steady state absorption, emission and time resolved emission spectroscopy. The molecule shows excited state intramolecular proton transfer (ESIPT) process with characteristics large Stoke shifted emission. Fluorescence enhancement of BHHB only in presence of Al ion is used as selective aluminium ion sensor in the sub-nano molar scale in aqueous solution.

Proton transfer inhibited charge transfer in a coumarinyl chalcone: Hassle free detection of chloroform vapor in alcohol medium and in neat solution.

The photophysical aspects of a synthesized coumarinyl chalcone derivative 3-((2E, 4E)-5-(4-(dimethylamino) phenyl) penta-2, 4-dienoyl)-4-hydroxy-2H-chromen-2-one (DPPHC) were explored. DPPHC shows excited state intramolecular proton transfer (ESIPT) suppressed excited state intramolecular charge transfer (ESICT) as evidenced from steady state and time resolved spectroscopic analysis. Interestingly, DPPHC behaves as a strong red emitter solely in chloroform and dichloromethane semi-polar solvents exclusively.

Effect of temperature and salts on niosome-bound anti-cancer drug along with disruptive influence of cyclodextrins.

Encapsulation of a persuasive anticancer drug (Sanguinarine, SGR) within microheterogeneous environment of niosome has been investigated. Utilizing steady-state and time-resolved spectroscopic methods the effects of extrinsically added salts and temperature on the photophysical properties of niosome-bound bio-active drug have been explored thoroughly. The prototropic (alkanolamine⇌ iminium) equilibrium of SGR is found to be preferentially favored toward the neutral form inside the hydrophobic interior of niosome.

Sphingomyelin-induced structural modification of native human hemoglobin and its chemically and thermally disrupted secondary structure: A photophysical exploration.

Sphingomyelin-induced structural modification of Human Hemoglobin (Hb) has been investigated in its native and unfolded conformers that are partially denatured in presence of ∼ 4 M urea, completely denatured in ∼ 8 M urea and thermally disrupted (at ∼ 65 °C) state. The absorption studies unveil ground state complexation between Hb and SM. From steady-state fluorescence and quenching studies alteration of the micro-environments around Trp residues of Hb in above mentioned different cases has been determined.

How is the interaction of a chloride channel blocker with phospholipids influenced by divalent metal ions? Effect of unsaturation on the lipid side chain.

The present study reveals the effect of various divalent ions (Ca, Mgand Zn) on the binding interaction of a prospective chloride channel blocker, 9-methylanthroate (9MA), with liposome membranes, namely, dimyristoylphosphatidylcholine (DMPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). The liposome membranes DMPC and POPC differ in the unsaturation of the side-chain. The drug (9MA) is found to experience a greater degree of partitioning into the POPC lipid bilayer (containing unsaturated side-chain) in comparison to DMPC (containing saturated side-chain).

Imine-Amine Tautomerism vs Keto-Enol Tautomerism: Acceptor Basicity Dominates Over Acceptor Electronegativity in the ESIPT Process through a Six-Membered Intramolecular H-Bonded Network.

Photophysical properties of a synthesized asymmetric two-way proton transfer molecule 3-(benzo[]thiazol-2-yl)-2-hydroxy-5-methoxybenzaldehyde () were studied in detail. could undergo excited-state intramolecular proton transfer (ESIPT) involving a 6-membered H-bonded network toward either the N or the O atom present in the molecule as proton acceptors. From tedious spectroscopic dissection, however, it was established that ESIPT was driven exclusively toward the N center over the O center in the solid state as well as in the solution phase.

Photophysical Properties of an Azine-Linked Pyrene-Cinnamaldehyde Hybrid: Evidence of Solvent-Dependent Charge-Transfer-Coupled Excimer Emission.

We report the photophysical properties of a synthetic asymmetric azine-based compound (17,18)-4'-(()-3-phenylallylidene)-1'-(dimethylamino)-1-((pyren-8-yl)methylene)hydrazine (). The molecule shows an appreciable red shift in the emission maximum in a wide range of solvents. In water, shows the characteristic feature of excimer formation exclusively.

Evaluating the merit of a diethylamino coumarin-derived thiosemicarbazone as an intramolecular charge transfer probe: efficient Zn(ii) mediated emission swing from green to yellow.

We report the synthesis and photophysical properties of a coumarin based probe (1E)-1-(1-(7-(diethylamino)-2-oxo-2H-chromen-3-yl) ethylidene) thiosemicarbazide (DIDOT). DIDOT shows a polarity dependent change in the emission maxima in the solution phase. This is explained by the increased dipole moment in the excited state by an intramolecular charge transfer (ICT) process.

Comparative Photophysical Study of Differently Substituted Cinnamaldehyde-Based Chalcones: From Intramolecular Charge Transfer to Fluorogenic Solvent Selectivity.

We synthesized three cinnamaldehyde-based chalcone derivatives, (2E,4E)-1-(2-hydroxyphenyl)-5-phenylpenta-2,4-dien-1-one (), (2E,4E)-5-(4-(dimethylamino)phenyl)-1-phenylpenta-2,4-dien-1-one (), and (2E,4E)-5-(4-(dimethylamino)phenyl)-1-(2-hydroxyphenyl)penta-2,4-dien-1-one (). The molecule was totally nonfluorescent. Exclusion of a phenolic -OH moiety from along with the introduction of a dimethylamino moiety in resulted in excellent excited-state charge-transfer properties in the solution phase.

Unsaturation of the phospholipid side-chain influences its interaction with cyclodextrins: A spectroscopic exploration using a phenazinium dye.

The interaction of a cationic photosensitizer Safranin-O with liposome membranes having similar surface charge (negative) but differing in the presence of saturation on the lipid side-chain has been studied. To this end, dimyristoyl-l-R-phosphatidylglycerol (DMPG) and 1,2-dioleoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DOPG) phospholipids were employed to prepare small unilamellar vesicles. The dye is found to bind in the headgroup region of both the liposome membranes with significantly higher affinity to DOPG lipid containing unsaturated side chain.

Host sensitized lanthanide photoluminescence from post-synthetically modified semiconductor nanoparticles depends on reactant identity.

This work investigates the photoluminescence characteristics where cadmium selenide (CdSe) and zinc sulfide (ZnS) nanoparticles are treated post-synthetically by the trivalent lanthanide cations (Ln) [Ln = Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb] separately to form either CdSe/Ln or ZnS/Ln nanoparticles. Host sensitized Ln emission was found to be present only in CdSe/Eu, CdSe/Tb, ZnS/Eu, ZnS/Tb and ZnS/Yb nanoparticles. In all the cases tuning of emission of the nanoparticles has been observed, irrespective of the presence or absence of host sensitization.

CHEF-Affected Fluorogenic Nanomolar Detection of Al by an Anthranilic Acid-Naphthalene Hybrid: Cell Imaging and Crystal Structure.

We report the synthesis of a novel hydrazine-bridged anthranilic acid-naphthalene conjugate ()-2-(benzamido)-'-((2-hydroxynaphthalen-1-yl) methylene) benzohydrazide () and its crystal structure. can detect Al by a sharp increment in fluorescence intensity (∼40 times) in aqueous methanolic medium. The limit of detection of towards Al is 1.

Interaction of a cationic amphiphile with monomeric and polymeric electrolytes: From morphological transition to associative phase separation.

The discrete effects of a series of structurally divergent monomeric viz. Sodium Chloride (NaCl), Tetra-butyl Ammonium Chloride (TBAC) and Sodium Benzoate (NaBz) and polymeric viz. Sodium Polystyrene Sulfonate (NaPSS) electrolytes towards the morphological and/or aggregation properties of Octadecyl-trimethyl Ammonium Bromide (OTAB) micelles have been quantified spectroscopically by means of the modulations of the absorption and emission spectral properties of an extrinsic anthracene-based probe 9-methyl anthroate (9-MA) within the concerned media.

Binding interaction of phenazinium-based cationic photosensitizers with human hemoglobin: Exploring the effects of pH and chemical structure.

The present study demonstrates a spectroscopic study on the interaction of two phenazinium-based cationic photosensitizers, namely, phenosafranin (PSF) and safranin-O (SO) with human hemoglobin (Hb) with particular emphasis on exploring the effects of pH and chemical structures of the dye molecules on the binding phenomenon. The protein (Hb) undergoes complex conformational transitions depending on the medium pH. The dye molecules exhibit a prominent fluorescence quenching following interaction with Hb under various experimental conditions (pH 3.

Employing a hydrazine linked asymmetric double naphthalene hybrid for efficient naked eye detection of F: Crystal structure with real application for F.

An asymmetric hydrazide, (12E, 13E)-2-((naphthalen-1-yl) methylene)-1-(1-(2-hydroxynaphthalen-6-yl) ethylidene) hydrazine (abbreviated as AH) is synthesized and characterized by standard techniques and crystal structure of AH has been obtained. The naked eye detection of F in aqueous acetonitrile (acetonitrile: water=7:3/v:v) by AH has been investigated by UV-Visible titration and in presence of other anions, the limit of detection being 1.31×10(M).

How Does Nanoconfinement within a Reverse Micelle Influence the Interaction of Phenazinium-Based Photosensitizers with DNA?

The major focus of the present work lies in exploring the influence of nanoconfinement within aerosol-OT (AOT) reverse micelles on the binding interaction of two phenazinium-based photosensitizers, namely, phenosafranin (PSF) and safranin-O (SO), with the DNA duplex. Circular dichroism and dynamic light-scattering studies reveal the condensation of DNA within the reverse micellar interior (transformation of the B-form of native DNA to ψ-form). Our results unveil a remarkable effect of the degree of hydration of the reverse micellar core on the stability of the stacking interaction (intercalation) of the drugs (PSF and SO) into DNA; increasing size of the water nanopool (that is, ) accompanies decreasing curvature of the DNA duplex structure with the consequent effect of increasing stabilization of the drug:DNA intercalation.

Differential Perturbation of the Protrotropic Equilibrium of a Biological Photosensitizer within Bile Salt Aggregates of Varying Hydrophobicity: A Fluorimetric Investigation.

The present work reveals the binding interactions of a credible cancer cell photosensitizer, harmane (HM), with some selected bile salt aggregates of dissimilar hydrophobicity viz. sodium deoxycholate (NaDC), sodium cholate (NaC) and sodium taurocholate (NaTC). The explicit variation of the prototropic equilibrium of the photosensitizer both in the ground and excited state has been utilized to scrutinize the interaction phenomena.

Binding mode dependent signaling for the detection of Cu: An experimental and theoretical approach with practical applications.

Two amido-schiff bases (3-Hydroxy-naphthalene-2-carboxylic acid pyren-1-ylmethylene-hydrazide and Naphthalene-2-carboxylic acid pyren-1-ylmethylene-hydrazide) have been synthesized having a common structural unit and only differs by a -OH group in the naphthalene ring. Both of them can detect Cu ion selectively in semi-aqueous medium in distinctly different output modes (one detects Cu by naked-eye color change where as the other detects Cu by fluorescence enhancement). The difference in the binding of Cu with the compounds is the reason for this observation.