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Title: Selective conformational control by excitation of NH imino vibrational antennas
Authors: Góbi, Sándor 
Reva, Igor 
Csonka, István Pál
Nunes, Cláudio M 
Tarczay, György
Fausto, Rui 
Issue Date: 7-Dec-2019
Publisher: Royal Society of Chemistry
Project: info:eu-repo/grantAgreement/POCI-01-0145-FEDER-016617/PT 
info:eu-repo/grantAgreement/EC/H2020/654148/EU/The Integrated Initiative of European Laser Research Infrastructures 
Serial title, monograph or event: Physical Chemistry Chemical Physics
Volume: 21
Issue: 45
Abstract: An imino group was used for the first time as a vibrational antenna to manipulate molecular conformations. Imino-thiol isomers of thioacetamide were generated upon UV-irradiation of its amino-thione tautomer isolated in argon matrices at 11 K. Selective and reversible conformational isomerizations were induced by narrowband near-IR irradiation tuned at the frequencies of the 2ν(NH) first stretching overtone of each imino-thiol isomer. The conformational isomerization concerns the change in the orientation of a remote -SH group, while the orientation of the imino (C[double bond, length as m-dash]NH) group remains the same. Supported by quantum chemical anharmonic computations, this allowed for a reliable, isomer-selective vibrational assignment of the four imino-thiol isomers extending now over the full mid-IR and near-IR ranges. It was found that the experimental IR intensities of the 2ν(NH) first stretching overtones (computed 4-5 km mol-1) of the imino-thiol forms are comparable to those of the ν(NH) stretching fundamentals (computed 2-4 km mol-1). This is the first time such a phenomenon is reported for an imine molecule. The kinetics of conformational isomerization was monitored in situ, indicating that the irradiation-induced processes are significantly faster than the tunneling-driven spontaneous cis-trans rotamerization of the -SH group. Quantum yields for the rotamerizations of the -SH group resulting from the vibrational excitation of a remote -NH group were estimated and found to be comparable to those observed for matrix-isolated carboxylic acids and amino acids, where conformational changes of the -OH group were induced by the direct vibrational excitation of 2ν(OH) first stretching overtones.
DOI: 10.1039/c9cp05370k
Rights: embargoedAccess
Appears in Collections:I&D CQC - Artigos em Revistas Internacionais

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