Solvent-dependent excited-state hydrogen transfer and intersystem crossing in 2-(2′-hydroxyphenyl)-benzothiazole

Handle URI:
http://hdl.handle.net/10754/564055
Title:
Solvent-dependent excited-state hydrogen transfer and intersystem crossing in 2-(2′-hydroxyphenyl)-benzothiazole
Authors:
Aly, Shawkat Mohammede ( 0000-0002-0455-1892 ) ; Usman, Anwar; Alzayer, Maytham; Hamdi, Ghada A.; Alarousu, Erkki; Mohammed, Omar F. ( 0000-0001-8500-1130 )
Abstract:
The excited-state intramolecular hydrogen transfer (ESIHT) of 2-(2′-hydroxyphenyl) benzothiazole (HBT) has been investigated in a series of nonpolar, polar aprotic, and polar protic solvents. A variety of state-of-the-art experimental methods were employed, including femto- and nanosecond transient absorption and fluorescence upconversion spectroscopy with broadband capabilities. We show that the dynamics and mechanism of ESIHT of the singlet excited HBT are strongly solvent-dependent. In nonpolar solvents, the data demonstrate that HBT molecules adopt a closed form stabilized by O-H⋯N chelated hydrogen bonds with no twisting angle, and the photoinduced H transfer occurs within 120 fs, leading to the formation of a keto tautomer. In polar solvents, owing to dipole-dipole cross talk and hydrogen bonding interactions, the H transfer process is followed by ultrafast nonradiative deactivation channels, including ultrafast internal conversion (IC) and intersystem crossing (ISC). This is likely to be driven by the twisting motion around the C-C bond between the hydroxyphenyl and thiazole moieties, facilitating the IC back to the enol ground state or to the keto triplet state. In addition, our femtosecond time-resolved fluorescence experiments indicate, for the first time, that the lifetime of the enol form in ACN is approximately 280 fs. This observation indicates that the solvent plays a crucial role in breaking the H bond and deactivating the excited state of the HBT. Interestingly, the broadband transient absorption and fluorescence up-conversion data clearly demonstrate that the intermolecular proton transfer from the excited HBT to the DMSO solvent is about 190 fs, forming the HBT anion excited state.
KAUST Department:
KAUST Solar Center (KSC); Physical Sciences and Engineering (PSE) Division; Chemical Science Program
Publisher:
American Chemical Society (ACS)
Journal:
The Journal of Physical Chemistry B
Issue Date:
12-Feb-2015
DOI:
10.1021/jp508777h
Type:
Article
ISSN:
15206106
Sponsors:
S.M.A. is grateful for the postdoctoral fellowship provided by Saudi Basic Industries Corporation (SABIC). The work reported here was supported by the King Abdullah University of Science and Technology.
Appears in Collections:
Articles; Physical Sciences and Engineering (PSE) Division; Chemical Science Program; KAUST Solar Center (KSC)

Full metadata record

DC FieldValue Language
dc.contributor.authorAly, Shawkat Mohammedeen
dc.contributor.authorUsman, Anwaren
dc.contributor.authorAlzayer, Maythamen
dc.contributor.authorHamdi, Ghada A.en
dc.contributor.authorAlarousu, Erkkien
dc.contributor.authorMohammed, Omar F.en
dc.date.accessioned2015-08-03T12:30:05Zen
dc.date.available2015-08-03T12:30:05Zen
dc.date.issued2015-02-12en
dc.identifier.issn15206106en
dc.identifier.doi10.1021/jp508777hen
dc.identifier.urihttp://hdl.handle.net/10754/564055en
dc.description.abstractThe excited-state intramolecular hydrogen transfer (ESIHT) of 2-(2′-hydroxyphenyl) benzothiazole (HBT) has been investigated in a series of nonpolar, polar aprotic, and polar protic solvents. A variety of state-of-the-art experimental methods were employed, including femto- and nanosecond transient absorption and fluorescence upconversion spectroscopy with broadband capabilities. We show that the dynamics and mechanism of ESIHT of the singlet excited HBT are strongly solvent-dependent. In nonpolar solvents, the data demonstrate that HBT molecules adopt a closed form stabilized by O-H⋯N chelated hydrogen bonds with no twisting angle, and the photoinduced H transfer occurs within 120 fs, leading to the formation of a keto tautomer. In polar solvents, owing to dipole-dipole cross talk and hydrogen bonding interactions, the H transfer process is followed by ultrafast nonradiative deactivation channels, including ultrafast internal conversion (IC) and intersystem crossing (ISC). This is likely to be driven by the twisting motion around the C-C bond between the hydroxyphenyl and thiazole moieties, facilitating the IC back to the enol ground state or to the keto triplet state. In addition, our femtosecond time-resolved fluorescence experiments indicate, for the first time, that the lifetime of the enol form in ACN is approximately 280 fs. This observation indicates that the solvent plays a crucial role in breaking the H bond and deactivating the excited state of the HBT. Interestingly, the broadband transient absorption and fluorescence up-conversion data clearly demonstrate that the intermolecular proton transfer from the excited HBT to the DMSO solvent is about 190 fs, forming the HBT anion excited state.en
dc.description.sponsorshipS.M.A. is grateful for the postdoctoral fellowship provided by Saudi Basic Industries Corporation (SABIC). The work reported here was supported by the King Abdullah University of Science and Technology.en
dc.publisherAmerican Chemical Society (ACS)en
dc.titleSolvent-dependent excited-state hydrogen transfer and intersystem crossing in 2-(2′-hydroxyphenyl)-benzothiazoleen
dc.typeArticleen
dc.contributor.departmentKAUST Solar Center (KSC)en
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
dc.contributor.departmentChemical Science Programen
dc.identifier.journalThe Journal of Physical Chemistry Ben
kaust.authorAly, Shawkat Mohammedeen
kaust.authorUsman, Anwaren
kaust.authorAlarousu, Erkkien
kaust.authorMohammed, Omar F.en
kaust.authorAlzayer, Maythamen
kaust.authorHamdi, Ghada A.en
All Items in KAUST are protected by copyright, with all rights reserved, unless otherwise indicated.