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The Control of the Cholesteric Pitch by Some Azo Photochemical Chiral Switches
Author(s) -
Pieraccini Silvia,
Gottarelli Giovanni,
Labruto Riccardo,
Masiero Stefano,
Pandoli Omar,
Spada Gian Piero
Publication year - 2004
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200400463
Subject(s) - photostationary state , moiety , isomerization , photoisomerization , photochemistry , chemistry , reflection (computer programming) , molecular switch , cholesteric liquid crystal , visible spectrum , photochromism , liquid crystal , crystallography , stereochemistry , materials science , organic chemistry , molecule , optoelectronics , computer science , programming language , catalysis
A few chiral azo compounds, which undergo reversible photochemical switching, are presented. Of these, the most interesting contain the binaphthyl moiety and belong to the C 2 (derivatives 1 and 2 ) or C 1 symmetry group (derivatives 3 and 4 ). These binaphthyl compounds display intense CD and high β values. Photochemical switching has profound effects on both the CD and β values of these compounds; in the case of compound 3 , the sign of β changes upon isomerisation. Compound 2 has, to our knowledge, the highest β of the switches reported in the literature and also seems the most interesting owing to its fast response to photochemical stimuli. Nematic phases can be transformed into cholesteric phases with reflection bands in the visible region by doping with reasonable amounts of 1 and 2 . The reflection colours can be changed reversibly by photoisomerisation of the switches. Thermal reversion of the colourless UV photostationary state to the green isomeric EE state or to intermediate coloured states is temperature dependent. This can allow the thermal history of a sample to be traced.