Photoisomerization of cis-1-(2-naphthyl)-2-phenylethene in methylcyclohexane at 77 K: no hula-twist.
The cis-trans photoisomerization of cis-1-(2-naphthyl)-2-phenylethene (c-NPEA and c-NPEB) was studied in methylcyclohexane glass at 77 K. The progress of the reaction was followed by fluorescence spectroscopy. Formation of the extended trans conformer (t-NPEB) is revealed by the growth of sharp vibronic bands on the broad structureless fluorescence spectrum of c-NPE. Principal component analysis with self-modeling of a matrix consisting of spectra generated by irradiation of c-NPE at different excitation wavelengths and spectra of t-NPE measured under the same conditions as a function of excitation wavelength reveals that the diabatic photoisomerization is a completely conformer-specific one-bond twist process: c-NPEB --> t-NPEB. These observations are consistent with observations in solution at ambient temperature. They demonstrate unequivocally that free volume restrictions imposed by the amorphous glassy environment do not open a hula-twist process.
Saltiel
Jack
J
Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390, USA. saltiel@chem.fsu.edu
Krishna
Tallapragada S R
TS
Turek
Andrzej M
AM
D003080:Cold Temperature; D003510:Cyclohexanes / Q000737:chemistry*; D005030:Ethylenes / Q000737:chemistry*; D007536:Isomerism; D008968:Molecular Conformation; D009281:Naphthalenes / Q000737:chemistry*; D010777:Photochemistry; D013050:Spectrometry, Fluorescence
D003510:Cyclohexanes; D005030:Ethylenes; D009281:Naphthalenes; C036216:ethylene