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Photoinduced Formation of a Cryptand from a Coronand: An Unexpected Switch in Cation Binding Affinity
Author(s) -
McSkimming Gordon,
Tucker James H. R.,
BouasLaurent Henri,
Desvergne JeanPierre,
Coles Simon J.,
Hursthouse Michael B.,
Light Mark E.
Publication year - 2002
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 - 10.1002/1521-3765(20020802)8:15<3331::aid-chem3331>3.0.co;2-c
Subject(s) - cryptand , chemistry , excimer , crown ether , stoichiometry , photochromism , photochemistry , intramolecular force , metal , crystallography , fluorescence , cycloaddition , inorganic chemistry , stereochemistry , organic chemistry , ion , physics , quantum mechanics , catalysis
Aza‐crown ethers 2 and 3 with anthracene‐containing pendant arms have been synthesised and characterised. Both compounds bind Group 1 metal cations in solution, forming complexes of 1:1 stoichiometry. The properties of compound 2 and its complexes have been studied by a range of techniques, including NMR, UV and fluorescence spectroscopy and X‐ray crystallography. The pendant arms can adopt either a cis or a trans geometry, the cis geometry favoured with larger cations. The geometry of the complex affects the fluorescence properties of the system, with larger cations giving higher excimer/monomer ratios. Upon irradiation at λ >300 nm, coronand 2 forms the cryptand 5 through a reversible intramolecular [4π+4π] cycloaddition reaction. The rates of the forward and reverse reactions of this photochromic process are cation dependent; in particular the rate of the thermal reverse reaction is decreased by smaller cations and increased by larger cations, especially Rb + . The metal binding constants in methanol for 2 and 5 have been determined, revealing that the cryptand 5 binds Na + and Rb + more weakly than crown ether 2 by over two orders of magnitude.