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ISSN: 1430-4171 (electronic version)

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Abstract Volume 8 Issue 1 (2003) pp 41-46

A Simple Pulse-Probe Experiment Based on Photochromism

Catherine C. Kitts and Benjamin A. DeGraff*

Department of Chemistry, James Madison University, Harrisonburg, VA 22807, degrafba@jmu.edu
Received June 27, 2002. Accepted September 18, 2002

Published online: 10 December 2002

Abstract. A series of experiments suitable for undergraduates based on photochromism is presented. The experiments involve simple kinetic spectroscopy, transient absorption, NMR, and computational techniques. Specifically, experiments based on the kinetics and transient absorption of 1',3'-dihydro-1',3',3'-trimethyl-6-nitrospiro[2H-1-benzopyran-2-2'-(2H)-indole] (I) in several solvents of differing polarity are presented. The kinetics show a first-order rate law for all solvents. Temperature studies yield enthalpies and entropies that depend on the solvent used. The transient absorption spectra in polar solvents are blue-shifted compared to nonpolar solvents. Additional experiments, using ¹H NMR to prove that only one intermediate is formed when the spiro compound is irradiated with UV light are described. Results from Spartan modeling calculations regarding the relative stability of possible intermediates are discussed. The experiments can be extended for semester projects.

Key Words:  Laboratories and Demonstrations; physical chemistry; photochromism; kinetics; pulse-probe techniques; transient absorption spectroscopy

(*) Corresponding author. (E-mail: degrafba@jmu.edu)

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Issue date: February 1, 2003

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