New benzopyranocarbazoles: synthesis and photochromic behaviour
authors Oliveira, MM; Salvador, MA; Coelho, PJ; Carvalho, LM
journal TETRAHEDRON
author keywords photochromism; benzopyranocarbazoles; naphthopyrans; heterocycles; spectrokinetic; hydroxybenzo[a]carbazoles
keywords NAPHTHOPYRANS; INTERMEDIATE; LENSES; SYSTEM
abstract The synthesis of three new benzopyranocarbazoles (= [indole]naphthopyrans) from hydroxybenzo[a]carbazoles is described. The photochromic properties of these novel compounds were investigated under flash photolysis and continuous irradiation. Compared to known [indole]benzopyrans these new compounds showed a significant bathochromic shift in the spectra of the open forms, an increase in colourabilities and slower ring closure kinetics. The photochromic behaviour of compound 4 has been further investigated. Continuous near-UV irradiation led to the formation of one photoisomer (TC) that was subsequently partially converted, to the other (TT). Thermal reversion of the preirradiated system to the original form was only partial and followed a monoexponential decay involving the back-conversion of the TC-isomer to the uncoloured closed form (CF). The thermally stable TT-isomer could only be photobleached with visible light. This process was shown to proceed through a fast photoconversion TT --> TC followed by the thermal path TC --> CF. Thermal relaxation of the activated system was also studied at various temperatures. (C) 2005 Elsevier Ltd. All rights reserved.
publisher PERGAMON-ELSEVIER SCIENCE LTD
issn 0040-4020
year published 2005
volume 61
issue 7
beginning page 1681
ending page 1691
digital object identifier (doi) 10.1016/j.tet.2004.12.055
web of science category Chemistry, Organic
subject category Chemistry
unique article identifier WOS:000226915200002
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journal impact factor 2.377
5 year journal impact factor 2.255
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