The photophysical behaviours of 2,3,6,7-tetrahydro-8-hydroxy-1H, 5H-benzo[i, j] quinolizine-9-carboxaldehyde (THBQC), a molecule having both the intramolecular excited state donor acceptor charge transfer and six member intramolecular hydrogen bonded proton transfer sites, have been investigated by steady state and time resolved spectroscopy in combination with quantum chemical calculations. The observed spectral characteristics of THBQC with variation of solvent properties, pH and temperature of the medium confirm the existence of different neutral and ionic species in the ground and excited states. Comparatively less solvent polarity dependent red shifted emission band of THBQC in all solvents is attributed to excited state intramolecular proton transfer of the closed conformer leading to keto-enol tautomerism but not of intramolecular charge transfer process. In polar solvents, apart from the proton transfer emission band, another band at higher energy region is attributed to the emission from the open solvated form. Evaluation of the potential energy surfaces by quantum chemical calculations using Density functional theory (DFT) and Hartree-Fock (HF) levels point towards the possibility of proton transfer reaction in the first excited state and correlate well with the experimental findings. © 2007 Elsevier B.V. All rights reserved.

NIKHIL GUCHHAIT

Chemistry

S MAHANTA

R B SINGH

D NATH

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 Photochemistry and Photobiology A: Chemistry

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

The ground and excited state properties of 1-hydroxy-2-naphthaldehyde (HN12) towards proton transfer reaction have been elaborately investigated on the basis of steady state absorption and emission, time-resolved fluorescence spectroscopy and quantum chemical calculations by ab initio (Hartree-Fock) and density functional theory (DFT) methods. The molecule HN12 exists as closed (intramolecular hydrogen bonded) and open conformer and their anions, and the hydrogen bonded solvated cluster in the ground state. The closed conformer on excitation undergoes photo-induced keto-enol tautomerism across the pre-existing intramolecular hydrogen bond (IMHB) and shows a red shifted emission band for the keto tautomer. Theoretically a significant change of some structural parameters such as Od-H1 bond length, Od⋯H1⋯Oa bond angle and charge distribution at the proton translocation site in the excited state favours intramolecular proton transfer process. Calculated potential energy curves along the proton transfer coordinate at the pre-existing hydrogen bonding site by DFT level account well for the feasibility of a barrierless ultrafast excited state intramolecular proton transfer reaction in HN12 molecule. © 2006 Elsevier B.V. All rights reserved.

Chemical Physics

Photo-physical properties of 1-hydroxy-2-naphthaldehyde: A combined fluorescence spectroscopy and quantum chemical calculations

A donor acceptor substituted aromatic system trans-3-(4-monomethylamino-phenyl)-acrylonitrile (MMAPA) has been synthesized and its photophysical behavior has been investigated in the solvent of different polarity by steady state absorption and emission, time-resolved emission and quantum chemical calculations. The observed dual fluorescence of MMAPA in polar aprotic solvents has been assigned to emission from the locally excited and twisted intramolecular charge transfer states. The low-energy emission in protic solvent is attributed to the hydrogen-bonded complex. Potential energy surfaces for the ground and excited states along the donor (-NHMe group) and acceptor (acrylonitrile group) twist coordinates have been calculated by time-dependent density functional theory (TDDFT) and time-dependent density functional theory-polarized continuum model (TDDFT-PCM) in the gas phase and in acetonitrile solvent, respectively. Calculations predict that the stabilized excited state along the twist coordinate is responsible for the solvent dependent red shifted charge transfer emission. It is found that the twisting along the donor site is energetically favorable compared to that of the acceptor site. The canonical crossing of the excited states for the twisting of the donor group and localized nitrogen lone pair orbital of -NHMe group at the perpendicular configuration with respect to p-orbitals of benzene ring support TICT model for photo-induced charge transfer reaction in MMAPA molecule. © 2006 Elsevier B.V. All rights reserved.

Photophysical properties of trans-3-(4-monomethylamino-phenyl)-acrylonitrile: Evidence of twisted intramolecular charge transfer (TICT) process

The photophysical behavior of 3-hydroxy-2-napthaldehyde (HN32) has been investigated on the basis of steady state absorption and fluorescence spectroscopy, time-resolved emission spectroscopy and quantum chemical calculations. In the ground state, depending on the nature of solvents, HN32 exists as closed (intramolecular hydrogen bonded), open and intermolecular hydrogen bonded conformers. The closed conformer present in the hydrocarbon as well as other solvents, on excitation, undergoes intramolecular proton transfer across the pre-existing intramolecular hydrogen bond to form the keto tautomer having red shifted emission. In case of hydroxylic polar solvents, an additional low energy fluorescence band is attributed to the intermolecular hydrogen bonded solvated complex of HN32 molecule. Structural calculation and the theoretical potential energy curves along the proton transfer coordinate performed by ab initio and Density Functional Theory (DFT) account well the observed spectral characteristics of HN32 for the ground and excited states. © 2006 Elsevier B.V. All rights reserved.

Excited state intramolecular proton transfer in 3-hydroxy-2-naphthaldehyde: A combined study by absorption and emission spectroscopy and quantum chemical calculation

The photophysical behaviour of trans-methyl p-(dimethylamino) cinnamate (t-MDMAC) donor-acceptor system has been investigated by steady-state absorption and emission spectroscopy and quantum chemical calculations. The molecule t-MDMAC shows an emission from the locally excited state in non-polar solvents. In addition to weak local emission, a strong solvent dependent red shifted fluorescence in polar aprotic solvents is attributed to highly polar intramolecular charge transfer state. However, the formation of hydrogen-bonded clusters with polar protic solvents has been suggested from a linear correlation between the observed red shifted fluorescence band maxima with hydrogen bonding parameters (α). Calculations by ab initio and density functional theory show that the lone pair electron at nitrogen center is out of plane of the benzene ring in the global minimum ground state structure. In the gas phase, a potential energy surface along the twist coordinate at the donor (-NMe 2) and acceptor (-CH = CHCOOMe) sites shows stabilization of S 1 state and destabilization S2 and S0 states. A similar potential energy calculation along the twist coordinate in acetonitrile solvent using non-equilibrium polarized continuum model also shows more stabilization of S1 state relative to other states and supports solvent dependent red shifted emission properties. In all types of calculations it is found that the nitrogen lone pair is delocalized over the benzene ring in the global minimum ground state and is localized on the nitrogen centre at the 90° twisted configuration. The S1 energy state stabilization along the twist coordinate at the donor site and localized nitrogen lone pair at the perpendicular configuration support well the observed dual fluorescence in terms of proposed twisted intramolecular charge transfer (TICT) model. © 2005 Elsevier B.V. All rights reserved.

Photoinduced intramolecular charge transfer (ICT) reaction in trans-methyl p-(dimethylamino) cinnamate: A combined fluorescence measurement and quantum chemical calculations

A donor-acceptor substituted aromatic system (E)-3-(4-Methylamino-phenyl)- acrylic acid methyl ester (MAPAME) has been synthesized, and its photophysical behavior obtained spectroscopically has been compared with the theoretical results. The observed dual fluorescence from MAPAME has been assigned to emission from locally excited and twisted intramolecular charge transfer states. The donor and acceptor angular dependency on the ground and excited states potential energy surfaces have been calculated both in vacuo and in acetonitrile solvent using time dependent density functional theory (TDDFT) and TDDFT polarized continuum model (TDDFT-PCM), respectively. Calculation predicts that a stabilized twisted excited state is responsible for red shifted charge transfer emission. © 2006 American Chemical Society.

Journal of Physical Chemistry A

Photoinduced intramolecular charge transfer reaction in (E)-3-(4-methylamino-phenyl)-acrylic acid methyl ester: A fluorescence study in combination with TDDFT calculation

Photophysical properties of 2,3,6,7-tetrahydro-8-hydroxy-1H, 5H-benz[i, j] quinolizine-9-carboxaldehyde: Evidence of excited state intramolecular proton transfer but not of intramolecular charge transfer process

Journal	Journal of Photochemistry and Photobiology A: Chemistry
Publisher	-
ISSN	1010-6030
Open Access	No