title: Photochromism of a merocyanine dye bound to sulfonatocalixarenes: effect of pH and the size of macrocycle on the kinetics.
abstract: The effect of 1:1 complex formation on the photochromic behavior of the merocyanine isomer of a nitro-substituted spirobenzopyran dye was studied in aqueous solution using 4-sulfonatocalixarene (SCXn) cavitands possessing four or eight phenol units. The binding constants were independent of the size of the macrocycle, and about 7-fold more stable associates were produced at pH 2.3 than in slightly alkaline solution. The complexation with SCXn diminished the acidity of protonated merocyanine (trans-MCH(+)) and precluded its photoinitiated transition to spirobenzopyran form, but did not affect the reactions in basic media. Upon exposure to light, the complexed trans-MCH(+) was converted to cis isomer. The association with 4-sulfonatocalix[4]arene slowed down the thermal back reaction in the dark to a larger extent than the confinement to 4-sulfonatocalix[8]arene. Both the activation energy and the Arrhenius A factor were significantly larger when the smaller, more rigid macrocycle served as a host.
authors.affiliation: Institute of Molecular Pharmacology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, P.O. Box 17, 1525 Budapest, Hungary.
authors.forename: Zsombor
authors.initials: Z
authors.lastname: Miskolczy
authors.forename: László
authors.initials: L
authors.lastname: Biczók
mesh_terms: D047250:Calixarenes / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007536:Isomerism; D007700:Kinetics; D008027:Light; D011522:Protons; D011744:Pyrimidinones / Q000737:chemistry*; D013141:Spiro Compounds / Q000737:chemistry; D013451:Sulfonic Acids / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D011522:Protons; D011744:Pyrimidinones; D013141:Spiro Compounds; D013451:Sulfonic Acids; D014867:Water; D047250:Calixarenes; C003954:merocyanine dye