In this work, we report intramolecular charge transfer (ICT) suppressed excited state intramolecular proton transfer (ESIPT) process in 4-(diethylamino)-2-hydroxybenzaldehyde (DEAHB). Photophysical properties of DEAHB have been extensively studied in different solvents with varying pH, polarity, and hydrogen bonding capability of the solvent using steady state and time-resolved spectroscopy. To establish the competition between the ICT and ESIPT processes in DEAHB, we have synthesized and studied the photophysical properties of 4-(diethylamino)-2-methoxybenzaldehyde (DEAMB) molecule where only the charge transfer process has been observed. Recently, we have reported simple Schiff base molecules (J. Phys. Chem. A 2012, 116, 10948) formed by condensation of DEAHB and hydrazine (5-(diethylamino)-2-[(4-(diethylamino) benzylidene)hydrazonomethyl]phenol (DDBHP) and N,N′-bis(4-N,N- (diethylamino)salisalidene)hydrazine (DEASH)), where charge transfer is assisted by the proton transfer process. In the present case, the DEAHB molecule shows the reverse phenomenon; i.e., charge transfer is suppressed by the proton transfer process. Comparing the photophysical properties of DEAHB with DEAMB it is also found that ICT process in DEAHB is suppressed by the ESIPT process. © 2013 American Chemical Society.

NIKHIL GUCHHAIT

Chemistry

S JANA

S DALAPATI

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Journal of Physical Chemistry A

Photophysical properties of 1-(2’-Hydroxy-5’-Chlorophenyl)-3-thio-5-oxo-1H-imidazo-[3,4-b] isoindol (HCHT) have been investigated thoroughly. Steady state and time resolved absorption and emission measurements in combination with theoretical calculation reveal that the synthesized molecule HCHT shows excited state thiolactim-thiolactum tautomerism through intramolecular hydrogen bonding between donor sulphur atom (-S-H) and acceptor nitrogen (N) atom. This is by far the first example where a sulfur atom is present as donor in an excited state proton transfer (ESIPT) process. Choice of sulfur atom in HCHT decelerates the irreversible ESIPT process compared to its oxygen atom donor analogue as evidence from excited state lifetime experiments. © 2019 Elsevier B.V.

Chemical Physics Letters

Thiolactim-Thiolactam photoisomerisation: Sulfur as proton donor for excited state proton transfer process

Photophysical properties of a newly designed synthetic compound DYMDAP have been investigated in combination with computational calculations. DYMDAP shows a solvent dependent emissive behavior which in non-polar solvents shows two distinct peaks along with a shoulder but with increasing polarity as also proticity of the solvents the intensity of each band varies significantly. Along with the two bands, a new band is observed in polar protic solvent due to the proton transfer (PT) in the excited state of the compound. Only in polar protic solvents, intensity of the PT band increases significantly whereas in non-polar or polar aprotic medium intensity is sparse. By comparing the spectral observations of DYMDAP with two control compounds DYMP and DYMDAB the proton transfer process is assigned to be due to solvent mediated and the proton transfer process is enhanced by the presence of charge transfer moiety. © 2018 Elsevier B.V.

Journal of Photochemistry and Photobiology A: Chemistry

A spectroscopic exploration of the influence of charge donor group on ESIPT process and its consequences in a salicylimine

A reduced Schiff base anionic receptor 1 [N,N′-bis-(2-hydroxy-5- nitro-benzyl)hydrazine] has been synthesized, characterized and reported as a selective chromogenic receptor for fluoride, acetate and phosphate anions over the other tested anions such as chloride, bromide, iodide and hydrogensulphite. Colorimetric naked-eye detection and UV-vis absorption spectroscopic techniques were used to distinguish the recognition behaviours towards various anions. The receptor-anion complexation mainly occurs via hydrogen bonding interactions which facile to generate the charge transfer band in the UV-vis spectra and cause large bathochromic shift as well as naked-eye colour change. Complexation stoichiometry, binding constant and free energy change due to complex formation were determined from Benesi-Hildebrand plot. The binding constant and the free energy change values are well interactive for spontaneous complexation. The experimental results have been correlated with the theoretical calculations using B3LYP hybrid functional and 6-311++G(d,p) basis set for both the receptor and complex by Density Functional Theory (DFT) method. © 2012 Elsevier B.V. All rights reserved.

Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy

Spectroscopic, colorimetric and theoretical investigation of Salicylidene hydrazine based reduced Schiff base and its application towards biologically important anions

Structural modification through binding interaction of plasma protein bovine serum albumin (BSA) with an extrinsic charge transfer fluorophore 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid (DMAPPDA) and its response to external perturbation due to interactions with surfactant sodium dodecyl sulphate (SDS) have been explored at physiological pH by steady state absorption, emission, fluorescence anisotropy, red edge excitation shift, far-UV circular dichroism and time resolved spectral measurements in combination with Molecular Docking and Molecular Dynamics (MD) simulation. Interaction of the probe with BSA is reflected by a small change in protein secondary structure with fluorescence enhancement and blue shift of probe emission. Molecular docking studies revealed that the probe binds to the hydrophobic cavity of sub-domain IIA of BSA. The distance for energy transfer from the tryptophan of BSA to the bound DMAPPDA measured by Fluorescence Resonance Energy Transfer is in good agreement with the molecular docking results. MD simulation predicts stabilization of the complex with respect to the bare molecule. Interaction of BSA and SDS with DMAPPDA supports the movement of the probe from hydrophilic free water region to a more restricted hydrophobic zone inside the protein. © 2012 The Royal Society of Chemistry and Owner Societies.

Photochemical and Photobiological Sciences

Exploring structural change of protein bovine serum albumin by external perturbation using extrinsic fluorescence probe: Spectroscopic measurement, molecular docking and molecular dynamics simulation

The nature of binding of specially designed charge transfer (CT) fluorophore at the hydrophobic protein interior of human serum albumin (HSA) has been explored by massive blue-shift (82 nm) of the polarity sensitive probe emission accompanying increase in emission intensity, fluorescence anisotropy, red edge excitation shift, and average fluorescence lifetimes. Thermal unfolding of the intramolecular CT probe bound HSA produces almost opposite spectral changes. The spectral responses of the molecule reveal that it can be used as an extrinsic fluorescent reporter for similar biological systems. Circular dichrosim spectra, molecular docking, and molecular dynamics simulation studies scrutinize this binding process and stability of the protein probe complex more closely. © 2012 Wiley Periodicals, Inc.

Biopolymers

Potential charge transfer probe induced conformational changes of model plasma protein human serum albumin: Spectroscopic, molecular docking, and molecular dynamics simulation study

A molecule having ethylenediamine unit with symmetrically attached aromatic frames has been synthesized, characterized and reported as a highly selective and sensitive chemosensor for Zn 2+ and Cd 2+ ion. UV-vis absorption and fluorescence emission spectra, quantum yield calculation, fluorescence lifetime measurement and the observed stability constant of metal-sensor complex support 1:1 complex formation for both Zn 2+ and Cd 2+ ion with the sensor. Enhancement of large Stokes shifted (130 nm for Zn 2+, 103 nm for Cd 2+) and polarity dependent emission bands were observed for Zn 2+ and Cd 2+ ions, while other transition metal ions Cr 3+, Fe 2+, Ni 2+, Co 2+, Cu 2+, Hg 2+ quench the fluorescence emission of the sensor. Ratiometric displacement of Cd 2+ ion from the complex by Zn 2+ ion supports the formation of more stable sensor-Zn 2+ complex over the sensor-Cd 2+ complex. Scanning electron micrographs show different structural morphology of the complexes. The experimental findings have been correlated with theoretical results using B3LYP functional and 6-311++G(d,p), LANL2DZ basis set for sensor and metal ion, respectively, by Density Functional Theory (DFT) method. © 2012 Elsevier B.V.

Fluorescent chemosensor for Zn(II) ion by ratiometric displacement of Cd(II) ion: A spectroscopic study and DFT calculation

Binding interaction of plasma protein bovine serum albumin (BSA) with external flexible charge transfer fluorophore 5-(4-dimethylamino-phenyl)-penta- 2,4-dienenitrile (DMAPPDN) has been explored at physiological pH (7.4) by steady state absorption, emission, fluorescence anisotropy, Red Edge Excitation Shift (REES), far-UV circular dichroism (CD), time resolved spectral measurements in combination with molecular docking and molecular dynamics (MD) simulation studies. Chemical denaturation of the protein bound probe by guanidine hydrochloride (GdnHCl) has also been tracked using the spectral response of DMAPPDN. Interaction of the probe with BSA is reflected by the massive blue shift of the fluorophore emission maxima (78 nm) with the enhancement of fluorescence intensity due to change of hydrophobic micro-environment of the probe compared to a little change in protein secondary structure. Benesi-Hildebrand plot reveals spontaneous formation of 1:1 BSA-DMAPPDN complex with binding constant 8.821 ± 0.01 × 10 3 M -1 and binding free energy change -5.359 kcal mol -1 . Molecular docking study supports the binding of probe in the hydrophobic cavity of sub domain IIA of BSA. The distance for energy transfer from tryptophan of BSA to DMAPPDN measured from fluorescence resonance energy transfer (FRET) results is in good agreement with results of molecular docking study. MD simulation predicts greater stability of BSA-DMAPPDN complex compared to the free protein. © 2011 Elsevier B.V.

Binding interaction between plasma protein bovine serum albumin and flexible charge transfer fluorophore: A spectroscopic study in combination with molecular docking and molecular dynamics simulation

Journal	Journal of Physical Chemistry A
Publisher	AMER CHEMICAL SOC
ISSN	1089-5639
Open Access	No