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.

NIKHIL GUCHHAIT

Chemistry

S C MAKHAL

A BHATTACHARYYA

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

Chemical Physics Letters

Spectral studies of 1-(2-hydroxy-5-chloro-phenyl)-3,5-dioxo-1H-imidazo-[3,4-b] isoindol (ADCL) in various solvents reveal the occurrence of excited state intramolecular proton transfer (ESIPT) process. Excitation at the shorter wavelengths preferentially leads to dual emission from an equilibrium mixture of excited state normal (N∗, lactim form) and tautomeric (T∗, lactam form) form due to the operation of proton transfer process. The proton transfer dynamics is found to be very slow in various organic solvents and it occurs in the nano-second time scale. This may be due to high energy barrier along the proton transfer coordinate through a strained four member hydrogen bonded network compared to the usual six member hydrogen bonded ring. © 2014 Elsevier B.V. All rights reserved.

Journal of Photochemistry and Photobiology A: Chemistry

Slow proton transfer dynamics of a four member intramolecular hydrogen bonded isoindole fused imidazole system: A spectroscopic approach to photophysical properties

This article presents the photophysical study of a pharmaceutically important isoindole fused imidazole derivative, namely 1-(2-hydroxy-5methyl- phenyl)-3,5-dioxo-1H-imidazo-[3,4-b] isoindole (ADII) using steady state absorption, emission and time resolved emission spectroscopy. The molecule possesses a four member intramolecular hydrogen bonded ring composed of OH and N atom suitable for intramolecular proton transfer process. Absorption study of ADII suggests the existence of its lactim and lactam tautomeric form in the ground state. The appearance of large Stokes shifted emission signifies lactim-lactam isomerization by excited state proton transfer reaction. Quantum chemical calculations at Density Functional Theory (DFT) (B3LYP/6- 311+G**) and Hartree-Fock (6-311+G**) levels have also been performed in support of the experimental findings. Both the level of theory suggests the existence of two tautomeric forms in the ground electronic state and the calculated potential energy surfaces along the proton transfer coordinate suggest the preference of excited state proton transfer reaction than the ground state with respect to activation barrier. The pH variance experiment is also carried out for investigating different absorbing and emitting species of ADII in aqueous and ACN medium. © 2013 Elsevier B.V. All rights reserved.

Lactim-lactam tautomerism through four member hydrogen bonded network in isoindole fused imidazole system: A combined spectroscopic and theoretical approach to photophysical properties

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.

Journal of Physical Chemistry A

Excited state intramolecular charge transfer suppressed proton transfer process in 4-(diethylamino)-2-hydroxybenzaldehyde

The molecule methyl-2-aminonicotinate (2-MAN) does not exhibit excited state intramolecular proton transfer (ESIPT), but its derivative 4-amino-2-methylsulfanyl-pyrimidine-5-carboxylic acid ethyl ester (AMPCE), widely used in the preparation of pyrimidopyrimidines as a protein kinase inhibitor, does exhibit ESIPT. Increasing acidic and basic character at the proton donor and proton acceptor sites by adding functional groups is found to be responsible for the large Stokes shifted ESIPT emission (Δν = 12 706 cm-1) in AMPCE. The photophysics of AMPCE have been explored on the basis of steady state and time resolved spectral measurements, quantum yield calculation with variation of polarity, as well as hydrogen bonding ability of solvents. Experimental findings have been correlated with the calculated structure and potential energy surfaces based on the intramolecular proton transfer model obtained by density functional theory (DFT). Properties based on the calculated excited state surfaces generated in vacuo and methanol solvent using time dependent density functional theory (TDDFT) and time dependent density functional theory polarized continuum model (TDDFT-PCM), respectively, show good agreement with the experimental findings. HOMO and LUMO diagrams also support the favorable ESIPT process in the first excited state potential energy surface. © 2013 The Royal Society of Chemistry and Owner Societies.

Photochemical and Photobiological Sciences

Functional group induced excited state intramolecular proton transfer process in 4-amino-2-methylsulfanyl-pyrimidine-5-carboxylic acid ethyl ester: A combined spectroscopic and density functional theory study

Anion (X) recognition fluorescent chemosensor 5-(4-Fluoro-phenyl)-2- hydroxy-nicotinonitrile (FP2HN) having both -NH and -OH groups in its two tautomeric forms has been synthesized and its excited state intramolecular proton transfer (ESIPT) reaction has been investigated by UV-vis, fluorescence, 1H NMR spectroscopy in combination with computational calculations. The experimental findings show that FP2HN selectively recognizes F -, AcO - and H 2PO 4 - ions through the formation of -N(O)H⋯X hydrogen bonding (HB) complex. The binding constant obtained by non-linear fit predicts the binding order of F - &gt; AcO - &gt; H 2PO 4 - &gt; Cl -. The ESIPT process of FP2HN is inhibited either by the fluoride induced deprotonation of acidic proton of FP2HN or by the formation of a strong -N(O)H⋯X intermolecular hydrogen bonding complex. Further insights into the recognition mechanism of the receptor-anion complexes using ab initio calculations have been performed which support the experimental binding affinity order of F - &gt; AcO - &gt; H 2PO 4 - &gt; Cl -. © 2012 Elsevier B.V. All rights reserved.

Selective anion recognition by inhibition of excited state intramolecular proton transfer process via hydrogen bonding interaction and efficient deprotonation: Spectroscopic and theoretical investigation

Journal	Data powered by TypesetChemical Physics Letters
Publisher	Data powered by TypesetElsevier B.V.
ISSN	0009-2614
Open Access	No