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Excited state intramolecular proton transfer of 2-hydroxy-1-naphthaldehyde semicarbazone: A combined fluorometric and quantum chemical study

Paper ID Volume ID Publish Year Pages File Format Full-Text
27384 44018 2011 8 PDF Available
Title
Excited state intramolecular proton transfer of 2-hydroxy-1-naphthaldehyde semicarbazone: A combined fluorometric and quantum chemical study
Abstract

Excited state intramolecular proton transfer (ESIPT) of 2-hydroxy-1-naphthaldehyde semicarbazone (2HNS) has been studied in n-heptane and methanol solvents exploiting absorption, steady state and time-resolved fluorometric techniques. Experimental results reveal that although the intramolecular proton transfer (IPT) reaction does not take place in the ground state (S0), the process is feasible in the lowest excited singlet state (S1). Ab initio quantum chemical calculations have been carried out to judge the feasibility of the IPT process in the different electronic states. Density functional theory (DFT) has been used for the ground state calculations while those relevant to the lowest excited singlet state have been performed exploiting the time dependent density functional theory (TDDFT) using the B3LYP functional at 6-31G** level. The distances of the transferable hydrogen from the oxygen atom (wherefrom it is dislocated during the IPT reaction) as well as the nitrogen atom (to which it gets attached) have been taken as the independent reaction coordinates. The calculations reveal that either of these two parameters may be used to monitor the progress of the prototropic process since both lead to the same prototropic species passing through the same transition state. Simulation of the potential energy curves (PECs) and potential energy surfaces (PESs) leads to visualize the advancement of the reaction. Calculations imply that formation of the tautomer in the S0 state leads to endothermicity, while the process is exothermic in the S1 state. The calculated activation energy (Eact) of the process also decreases in the excited state. Thus, although the reaction is not feasible in the ground state, both the thermodynamic (ΔH) and the kinetic (Eact) factors favor the prototropic process to occur in the S1 state. This article reveals that any of the suitably and logically chosen structural parameters giving the same value of the reaction parameters and resulting in the same transition state may serve as the reaction co-ordinate.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► ESIPT of 2-hydroxy-1-naphthaldehyde semicarbazone (2HNS) has been studied. ► 2HNS gives normal emission in methanol and dominantly tautomer emission in heptane. ► Ab initio quantum chemical calculation for the IPT process is carried out. ► ΔH and Eact factors favor the IPT process in the S1 state but not in the S0 state. ► Either of O17–H18 or H18–N20 distances may serve as the reaction coordinate.

Keywords
Excited state intramolecular proton transfer (ESIPT); Fluorescence; DFT calculation; Potential energy curve
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Excited state intramolecular proton transfer of 2-hydroxy-1-naphthaldehyde semicarbazone: A combined fluorometric and quantum chemical study
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 222, Issue 1, 5 July 2011, Pages 220–227
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us