The empirical correlation between hydrogen bonding strength and excited-state intramolecular proton transfer in 2-pyridyl pyrazoles

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

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Author(s)

  • Tsung-Yi Lin
  • Kuo-Chun Tang
  • Shen-Han Yang
  • Jiun-Yi Shen
  • Yi-Ming Cheng
  • Hsiao-An Pan
  • Pi-Tai Chou

Detail(s)

Original languageEnglish
Pages (from-to)4438-4444
Journal / PublicationJournal of Physical Chemistry A
Volume116
Issue number18
Online published10 Apr 2012
Publication statusPublished - 10 May 2012
Externally publishedYes

Abstract

A series of 2-pyridyl pyrazoles 1a and 1-5 with various functional groups attached to either pyrazole or pyridyl moieties have been strategically designed and synthesized in an aim to probe the hydrogen bonding strength in the ground state versus dynamics of excited-state intramolecular proton transfer (ESIPT) reaction. The title compounds all possess a five-membered-ring (pyrazole)N-H···N(pyridine) intramolecular hydrogen bond, in which both the N-H bond and the electron density distribution of the pyridyl nitrogen lone-pair electrons are rather directional, so that the hydrogen bonding strength is relatively weak, which is sensitive to the perturbation of subtle chemical substitution and consequently reflected from the associated ESIPT dynamics. Various approaches such as 1H NMR (N-H proton) to probe the hydrogen bonding strength and absorption titration to assess the acidity-basicity property were made for all the title analogues. The results, together with supplementary support provided by a computational approach, affirm that the increase of acidity (basicity) on the hydrogen bonding donor (acceptor) sites leads to an increase of hydrogen-bonding strength among the title 2-pyridyl pyrazoles. Luminescence results and the associated ESIPT dynamics further reveal an empirical correlation in that the increase of the hydrogen bonding strength leads to an increase of the rate of ESIPT for the title 2-pyridyl pyrazoles, demonstrating an interesting relationship among N-H acidity, hydrogen bonding strength, and the associated ESIPT rate. © 2012 American Chemical Society.

Citation Format(s)

The empirical correlation between hydrogen bonding strength and excited-state intramolecular proton transfer in 2-pyridyl pyrazoles. / Lin, Tsung-Yi; Tang, Kuo-Chun; Yang, Shen-Han et al.

In: Journal of Physical Chemistry A, Vol. 116, No. 18, 10.05.2012, p. 4438-4444.

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review