Photophysical investigation of synthesized probe BTNP shows it undergoes coupling of AIE and ESIPT in strictly non-polar medium, as opposed to conventional trend of AIEgens forming aggregates in ...water only. Hence, BTNP was used to generalize the definition of AIE phenomenon itself.
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Excited photophysics of a synthesized molecule namely 2-(benzodthiazol-2-yl)-5-nitrophenol (BTNP) have been studied using steady state and time resolved techniques. BTNP exhibits ESIPT exclusively in non-polar media with exceptional Stokes’ shift. In polar solvents anion formation of BTNP hampers the ESIPT process. Solid state emission spectral pattern matches reasonably well with that in non-polar medium. Dynamic light scattering showed the increment of particle size in heptane in comparison to water, a trend reversed to conventional trait of Aggregation Induced Emission (AIE) active molecules. Nitro substituent in BTNP reverses the conventional definition of a ‘good solvent’ and ‘bad solvent’, thereby promoting ESIPT in non-polar medium via aggregation. As all reports on AIE active compounds claim water to be the solvent capable of producing the effect, we have reversed the effect by simple change in substitution. Reversal of AIE phenomenon would certainly open up new avenues in future research on AIE active fluorophores.
Photophysical properties of a synthesized asymmetric two-way proton transfer molecule 3-(benzodthiazol-2-yl)-2-hydroxy-5-methoxybenzaldehyde (BTHMB) were studied in detail. BTHMB 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. The aforementioned deduction was based on spectral comparison with judicially designed molecules 2-hydroxy-5-methoxybenzaldehyde (HMB) and 2-(benzodthiazol-2-yl)-4-methoxyphenol (BTMP). In solution, the coexistence of the anionic and neutral forms of BTHMB in basic solvents dimethylsulfoxide (DMSO) and dimethylformamide (DMF) enables BTHMB to behave as a white light emitter. Thus, apart from establishment of directionality of ESIPT in double ESIPT probes, the current work deserves special merit as BTHMB can be considered as a standard in future designs involving red light and solvent-specific white light emitters.
A simple intramolecular charge transfer (ICT) compound, 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid methyl ester (DPDAME), has been documented to be a potential molecular reporter for probing ...microheterogeneous environments of a model transport protein bovine serum albumin (BSA) using spectroscopic techniques. Meteoric modifications to the emission profile of DPDAME upon addition of BSA come out to be a result of its binding to hydrophobic subdomain IIA. The highly polarity-sensitive ICT emission of DPDAME is found to be a proficient extrinsic molecular reporter for efficient mapping of native, intermediate, unfolded, and refolded states of the protein. Experimental data coupled with a reinforcing support from theoretical simulation using CHARMM22 software confirm the binding site of the probe to be the subdomain IIA of BSA, while FRET study reveals a remarkably close approach of our extrinsic molecular reporter to Trp-212 (in domain IIA): the distance between DPDAME and Trp-212 is 1.437 nm. The caliber of DPDAME as an external fluorescence marker also extends to the depiction of protein−surfactant (BSA−SDS) interaction to commendable fruition. Additionally, the protective action of small amounts of SDS on urea-denatured protein is documented by polarity-sensitive ICT emission of the probe. The present study also reflects the enhancement of the stability of BSA with respect to chemically induced denaturation by urea as a result of binding to the probe DPDAME.
Here, we report a Density Functional Theoretical (DFT) study on the photophysics of a potent Excited-State Intramolecular Proton Transfer (ESIPT) molecular system, viz., 10-hydroxybenzo
hquinoline ...(HBQ). Particular emphasis has been rendered on the assessment of the proton transfer reaction in HBQ in the ground and excited-states through elucidation and a careful perusal of the potential energy surfaces (PES). The non-viability of Ground-State Intramolecular Proton Transfer (GSIPT) process is dictated by a high-energy barrier coupled with no energy minimum for the proton transferred (K-form) form at the ground-state (S
0) PES. Remarkable reduction of the barrier along with thermodynamic stability inversion between the enol (E-form) and the keto forms (K-form) of HBQ upon photoexcitation from S
0 to the S
1-state advocate for the operation of ESIPT process. These findings have been cross-validated on the lexicon of analysis of optimized geometry parameters, Mulliken’s charge distribution on the heavy atoms, and molecular orbitals (MO) of the E- and the K-forms of HBQ. Our computational results also corroborate to experimental observations. From the modulations in optimized geometry parameters in course of the PT process a critical assessment has been endeavoured to delve into the movement of the proton during the process. Additional stress has been placed on the analysis of the intramolecular hydrogen bonding (IMHB) interaction in HBQ. The IMHB interaction has been explored by calculation of electron density
ρ(r) and the Laplacian ∇
2
ρ(r) at the bond critical point (BCP) using Atoms-In-Molecule (AIM) method and by calculation of interaction between σ⁎ of OH with the lone pair of the nitrogen atom using Natural Bond Orbital (NBO) analysis.
► Theoretical modelling of the photophysics of an ESIPT probe 10-hydroxybenzo
hquinoline (HBQ). ► Calculation of intramolecular hydrogen bond (IMHB) energy. ► Role of hyperconjugative charge transfer interaction in IMHB assessed by NBO perspective. ► Topological properties of IMHB analyzed from AIM view point. ► Computational results are assayed from direct comparison with experimental reports.
Photochromic Schiff bases 5-diethylamino-2-(4-diethylamino-benzylidene)-hydrazonomethyl-phenol (DDBHP) and N,N′-bis(4-N,N-diethylaminosalisalidene) hydrazine (DEASH) with both the proton and charge ...transfer moieties have been synthesized, and their photophysical properties such as excited state intramolecular charge transfer (ICT) and proton transfer (ESIPT) processes have been reported on the basis of steady-state and time-resolved spectral measurement in various solvents. The ground-state six-membered intramolecular hydrogen bonding network at the proton transfer site accelerates the ESIPT process for these compounds. Both the compounds show large Stokes-shifted emission bands for proton transfer and charge transfer processes. The hydrogen bonding solvents play a crucial role in these photophysical processes. Excited-state dipole moment of DDBHP and DEASH calculated by the solvatochromic method supports the polar character of the charge transfer excited state. Introduction of −NEt2 groups to the reported salicylaldehyde azine (SAA) Schiff base results an increase in fluorescence lifetime from femtosecond to picosecond time scale for the proton transfer process.
A new Schiff base compound 2-((benzylimino)-methyl)-naphthalen-1-ol (2BIMN1O) has been synthesized and characterized by (1)H NMR, (13)C NMR, DEPT, FT-IR and mass spectroscopic techniques. The ...significantly low fluorescence yield of the compound has been rationalized in connection with photo-induced electron transfer (PET) from the imine receptor moiety to the naphthalene fluorophore unit. Subsequently, an evaluation of the transition metal ion-induced modification of the fluorophore-receptor communication reveals a promising prospect for the title compound to function as a fluorosensor for Cu(2+) and Zn(2+) ions selectively, through remarkable fluorescence enhancement. While perturbation of the PET process in 2BIMN1O has been argued to be the responsible mechanism behind the fluorescence enhancement, the selectivity for these two metal ions has been interpreted on the grounds of an appreciably strong binding interaction. Particularly notable aspects regarding the chemosensory activity of the compound are its ability to detect the aforesaid transition metal ions down to the level of micromolar concentration (detection limit being 0.82 and 0.35 μM respectively), along with a simple and efficient synthetic procedure. Also the spectral modulation of 2BIMN1O in the presence of the transition metal ions paves the way for the construction of a calibration curve in the context of its fluorescence signaling potential.
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•Elucidation of photoinduced electron transfer (PET) process in a simple Schiff base.•Naked eye sensing of Cu(II) ion with ratiometric sensing potential.•Selective fluorescence ...sensing of Cu(II) and Zn(II) ions via perturbation of the PET process.•Sufficiently low limit of detection (up to ppm level).
A simple Schiff base compound 2-((cyclohexylmethylimino)-methyl)-naphthalen-1-ol (2CMIMN1O) has been synthesized and characterized by 1H NMR, 13C NMR and FT-IR spectroscopic techniques. A significantly low emission yield of the compound has been rationalized in anticipation with photo-induced electron transfer (PET) from the imine receptor moiety to the naphthalene fluorophore unit. Consequently, an evaluation of the transition metal ion-induced modification of the fluorophore-receptor communication reveals the promising prospect of the title compound to function as a chemosensor for Cu2+ and Zn2+ ions selectively, through remarkable fluorescence enhancement as well as visual changes. While perturbation of the PET process has been argued to be the plausible mechanism behind the fluorescence enhancement, the selectivity for these two metal ions has been interpreted on the grounds of an appreciably strong binding interaction. Particularly notable aspects regarding the chemosensory activity of the compound is its ability to detect the aforesaid transition metal ions down to the level of micromolar concentration (detection limit being 2.74 and 2.27ppm respectively), along with a simple and efficient synthetic procedure.
The excited-state intramolecular proton transfer (ESIPT) reaction of 1-hydroxy-2-naphthaldehyde (HN12) has been studied within the interior of the supramolecular assemblies of α-, β-, and ...γ-cyclodextrins (CD) and biomimicking environments of ionic (SDS) and non-ionic (TW-20) micelles. Fluorescence measurements are used to investigate the effect of various supramolecular assemblies on the ESIPT reaction by monitoring the large Stokes-shifted tautomer emission of HN12. Enhanced tautomer emission in the microencapsulated state predicts favorable ESIPT reaction in the supramoleuclar assemblies. Benesi−Hildebrand plots have been employed to ascertain that the stoichiometric ratios of the complexes formed between HN12 and CDs are 1:2, 1:1, and 1:1 for α-, β-, and γ-CD, respectively. The binding constants (K 1) and free-energy change (ΔG) for inclusion complexation are also determined from the linearized Benesi−Hildebrand plots. Steady-state fluorescence anisotropy, REES, excitation anisotropy, and fluorescence lifetime measurements are in line with other experimental findings. Differential action of urea on SDS and TW-20-bound probe has also been investigated.
Study of intra- and intermolecular hydrogen-bonding interaction and excited state proton transfer reaction has been carried out in 4-hydroxyacridine (4-HA) and its hydrated clusters theoretically. ...Density functional theory B3LYP/6-311++G(d,p) has been exploited to calculate structural parameters and relative energies of different conformers of 4-HA and its hydrates. The substantial impact of solvent reaction field on hydrogen-bond energies, conformational equilibrium, and tautomerization reaction in aqueous medium have been realized by employing Onsager and PCM reaction field methods, and the stability of the conformers of 4-HA is found to be profusely modulated by the electrostatic influence of the solvent. A deeper insight into the nature of H-bonding in 4-HA and its hydrated clusters has been achieved under the provision of natural bond orbital and atoms in molecule analysis. Elucidation of potential energy curves for proton transfer reaction reveals that an intrinsic and two-water-molecule-assisted proton transfer (PT) reaction in 4-HA is hindered by high energy barrier in the S1 surface, whereas single-water-assisted PT reaction is practically rendered barrierless. At the same time, the appreciably high barrier height of the ground state potential energy curve in all the cases unambiguously rules out the possibility of ground state proton transfer reaction.
Five new organotin(IV) complexes of compositions Me2SnL1 (1), Me2SnL2n (2), Me2SnL3 (3), Ph3SnL1Hn (4) and Ph3SnL3H (5) (where ...L1=(2S)-2-((E)-((Z)-4-hydroxypent-3-en-2-ylidene)amino)-3-(1H-indol-3-yl)propanoate, L2=(2S)-(E)-2-((2-hydroxybenzylidene)amino)-3-(1H-indol-3-yl)propanoate and L3=(2S)-(E)-2-((1-(2-hydroxyphenyl)ethylidene)amino)-3-(1H-indol-3-yl)propanoate were synthesized and spectroscopically characterized. The crystal structures of 1–4 were determined. For the dimethyltin derivative 2, a polymeric chain structure was observed as a result of a long Sn∙∙∙O contact involving the exocyclic carbonyl oxygen-atom from the tridentate ligand of a neighboring Sn-complex unit. The tin atom in this complex has a distorted octahedral coordination geometry, in which the long Sn-O bond is almost trans to the tridentate ligand nitrogen-atom. In contrast, the dimethyltin(IV) complexes 1 and 3 displayed discrete monomeric structures where the tin atom has distorted trigonal-bipyramidal geometry with the two coordinating L oxygen atoms defining the axial positions. On the other hand, 4 is a chain polymer in the solid state. The ligand-bridged Sn atoms adopt a trans-Ph3SnO2 trigonal-bipyramidal configuration with equatorial phenyl groups. A carboxylato oxygen atom from one and the hydroxyl oxygen of the successive ligand in the chain occupy the axial positions.
The solution structures were predicted by the use of 119Sn NMR chemical shifts. The photophysical properties of the complexes were investigated in the solid and in solution. The triphenyltin(IV) compound 4 was tested in detail ex vivo against A375 (human melanoma) cell line, exhibiting an IC50 value of 261nM to induce cell death as assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay without significant alteration of cytolysis as determined by lactate dehydrogenase (LDH) assay. Compound 4-mediated potent cell death was also determined by Live and Dead assay and caspase-mediated cleavage of poly-ADP ribose polymerase (PARP). Potent cell death activity was not observed in primary cells, like blood-derived peripheral mononuclear cells (PBMC). Compound 4 inhibited the diphenyl hexatriene (DPH) binding to cells and decreased the micro viscosity in a dose-dependent manner. Additionally, the ability of 4 and cyclodextrin (CD) to interact was determined by molecular modelling.
Five new organotin(IV) complexes viz., Me2SnL1 (1), Me2SnL2n (2), Me2SnL3 (3), Ph3SnL1Hn (4) and Ph3SnL3H (5) (where L1=(2S)-2-((E)-((Z)-4-hydroxypent-3-en-2-ylidene)amino)-3-(1H-indol-3-yl)propanoate, L2=(2S)-(E)-2-((2-hydroxybenzylidene)amino)-3-(1H-indol-3-yl)propanoate and L3=(2S)-(E)-2-((1-(2-hydroxyphenyl)ethylidene)amino)-3-(1H-indol-3-yl)propanoate were synthesized and characterized. The crystal structures of 1–4 were determined. Designed Ph3SnL1Hn4 demonstrated potent apoptotic activity in melanoma cells ex vivo. Display omitted
•Three dimethyltin(IV)- and two triphenyltin(IV) complexes have been synthesized.•The coordination pattern at the Sn(IV) center was established by X-ray diffraction.•Ph3SnL1H 4 exhibited potent apoptotic activity (IC50=261nM) in melanoma cells ex vivo.•Apoptosis was judged by Live & Dead and caspases cleavage assays etc.•The interaction ability between 4 and cyclodextrin was determined by modelling approach.
