Publication detail

4-OH coumarin based rotary switches: Tautomeric state and effect of the stator

YORDANOV, D. DENEVA, V. GEORGIEV, A. VASSILEV, N VALA, M. ZHIVKOV, I. ANTONOV. L

Original Title

4-OH coumarin based rotary switches: Tautomeric state and effect of the stator

Type

journal article in Web of Science

Language

English

Original Abstract

Two new 4-OH coumarin based rotary switches, containing fixed carbonyl groups in the rotor, have been synthesized and their properties have been studied by combined use of DFT calculations and molecular spectroscopy (UV-Vis absorbance and emission, NMR). It was found that the structure of the stator (naphthyl in 2 or quinolyl moiety in 3) and solvents polarity do not influence their azo-hydrazone tautomerism. Both compounds exist as keto (hydrazone) tautomers. The NMR data indicate a mixture of E (major) and Z (minor) keto form isomers in solution. The results are in very good agreement with ground state DFT calculations. The keto tautomers exhibit different emission behavior depending on the structure of the stators. Comparing to 2, more intensive emission and higher lifetime was observed in 3, where the formation of intramolecular hydrogen bonding of the hydrazone NH with the N atom of quinoline restricts the rotation of the stator. According to the spectral data and the TDDFT analysis the observed emission originates from the excitation of the keto tautomers and does not include excited state proton transfer. It was shown that the protonation is a suitable stimulus for E/Z switching in 2, where a possible mechanism is sketched. In the case of 3, the addition of acid leads to the pmtonation of the quinolyl nitrogen atom, which slightly affects the E/Z isomerization ratio.

Keywords

4-Hydroxycoumarin; Rotary switch; Molecular spectroscopy; DFT; Tautomerism; Photochemistry

Authors

YORDANOV, D.; DENEVA, V.; GEORGIEV, A.; VASSILEV, N; VALA, M.; ZHIVKOV, I.; ANTONOV. L

Released

11. 1. 2021

Publisher

ELSEVIER SCI LTD

Location

OXFORD

ISBN

0143-7208

Periodical

DYES AND PIGMENTS

Year of study

184

Number

108861

State

United Kingdom of Great Britain and Northern Ireland

Pages from

1

Pages to

12

Pages count

12

URL

https://www.sciencedirect.com/science/article/pii/S0143720820315588?via%3Dihub

BibTex

@article{BUT172907,
  author="YORDANOV, D. and DENEVA, V. and GEORGIEV, A. and VASSILEV, N and VALA, M. and ZHIVKOV, I. and ANTONOV. L",
  title="4-OH coumarin based rotary switches: Tautomeric state and effect of the stator",
  journal="DYES AND PIGMENTS",
  year="2021",
  volume="184",
  number="108861",
  pages="1--12",
  doi="10.1016/j.dyepig.2020.108861",
  issn="0143-7208",
  url="https://www.sciencedirect.com/science/article/pii/S0143720820315588?via%3Dihub"
}