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Solvatochromism of -Naphthol Kyril M. Solntsev and Dan Huppert
 

Summary: Solvatochromism of -Naphthol
Kyril M. Solntsev and Dan Huppert
School of Chemistry, Raymond and BeVerly Sackler Faculty of Exact Sciences, Tel-AViV UniVersity,
Tel AViV 69978, Israel
Noam Agmon*
The Fritz Haber Research Center, Department of Physical Chemistry, The Hebrew UniVersity,
Jerusalem 91904, Israel
ReceiVed: May 20, 1998; In Final Form: August 5, 1998
Excitation and emission fluorescence spectra of 2-naphthol and 2-methoxynaphthalene were measured in a
series of pure solvents. The spectral shifts are correlated by the Kamlet-Taft parameters (*, , and R). As
judged from the * dependence, both molecules have a negligibly small dipole moment in their ground
electronic state, which increases in the excited (S1) state. However, the majority of the Stokes shift is due to
hydrogen-bonding rather than to dipole-dipole interactions. By comparing the shifts for the two compounds,
it is demonstrated that the dependence in 2-naphthol is due exclusively to a hydrogen bond donated from
its hydroxylic hydrogen atom to the solvent. This bond becomes stronger upon excitation and hence produces
a bathochromic shift. We find R dependence only in the excitation spectrum, indicating that protic solvents
stabilize the ground state by donating a hydrogen bond to the hydroxylic oxygen. This bond breaks following
excitation to S1 but re-forms following proton transfer.
1. Introduction
Proton-transfer reactions are a common example of acid-

  

Source: Agmon, Noam - Institute of Chemistry, Hebrew University of Jerusalem

 

Collections: Chemistry