Journal
JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY
Volume 162, Issue 2-3, Pages 473-479Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/S1010-6030(03)00388-5
Keywords
Schiff bases; salicylideneanilines; solvatochromism; thermochromism; photochromism
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A series of salicylideneaniline (SA) derivatives 1-3 were prepared to study the substituent effect on the chromic properties. Compounds 1 and 3, introduced naphthyl group on the A ring in the parent compound SA, exhibited the solvatochromism, thermochromism and photochromism, while compound 2, introduced the naphthyl group on the B ring in SA, did not show the solvatochromism or thermochromism. The discussion in this study is mainly focused on the behaviour of compounds 1 and 2. The UV absorption spectra of 1 dramatically changed with increasing the solvent polarity as well as cooling temperature, suggesting that 1 takes Z-NH form in polar solvents at room temperature or even in non-polar solvents at below 120 K. Compound 1 emits fluorescence (FL) only at low temperature with small Stokes shift, while 2 exhibits fluorescence emission with considerably large Stokes shift. On UV irradiation, 1 in benzene underwent intramolecular hydrogen atom transfer to give E-NH form. The large Stokes shift observed in 2 indicates that 2 takes E-OH form even at low temperature in any solvents, and underwent intramolecular hydrogen atom transfer in the excited state to give Z-NH form, which emits the fluorescence at low temperature, or undergoes isomerization around C=C double bond to give E-NH form. The potential energy diagrams for 1 and 2 were also determined. (C) 2004 Elsevier B.V. All rights reserved.
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