Potentialities of diffuse reflectance laser-induced techniques in solid phase: A comparative study of benzophenone inclusion within p- tert-butylcalixarenes, silicalite and microcrystalline cellulose

Diffuse reflectance and laser-induced techniques were used to access photochemical and photophysical processes in solid phases, namely calix[ n]arenes ( n is the number of phenolic units in the ring), organic substances which are capable of forming inclusion complexes with several neutral organic su...

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Bibliographic Details
Published in:	Journal of photochemistry and photobiology. A, Chemistry. Vol. 153; no. 1; pp. 11 - 18
Main Authors:	Vieira Ferreira, L.F, Vieira Ferreira, M.R, Oliveira, A.S, Moreira, J.C
Format:	Journal Article
Language:	English
Published:	Lausanne Elsevier B.V 01-11-2002 Elsevier Science
Subjects:	Atomic and molecular physics Benzophenone Calixarenes Diffuse reflectance Exact sciences and technology Flash photolysis Fluorescence and phosphorescence spectra Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion) Inclusion complexes Microcrystalline cellulose Molecular properties and interactions with photons Physics Room temperature phosphorescence Silicalite Diffuse reflectance Calixarenes Microcrystalline cellulose Room temperature phosphorescence Silicalite Inclusion complexes Flash photolysis Benzophenone Diffuse reflection Phosphorescence spectrometry Calixarene Radiative lifetimes Experimental study Quantum yield Molecular sieves Ambient temperature Inclusion compounds Cellulose derivatives Benzenic compound Organic compounds
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Summary:	Diffuse reflectance and laser-induced techniques were used to access photochemical and photophysical processes in solid phases, namely calix[ n]arenes ( n is the number of phenolic units in the ring), organic substances which are capable of forming inclusion complexes with several neutral organic substances and metal ions. We have used p- tert-butylcalix[4], p- tert-butylcalix[6] and p- tert-butylcalix[8]arenes as solid matrixes and benzophenone as probe. A comparative study is presented here, mainly using the results obtained with the calix[6]arene as host and those obtained with two other electronically inert supports: microcrystalline cellulose and silicalite, a hydrophobic zeolite. In all substrates, room temperature phosphorescence was obtained in air equilibrated samples. The decay times vary greatly and the largest lifetime was obtained for silicalite, where benzophenone is included into hydrophobic channels. Calix[6]arene and cellulose provide full protection against oxygen quenching while silicalite only protects the guest molecule partially. Calixarene molecules provide larger hydrophobic cavities than silicalite and also a better selectivity towards the guest size. This selectivity does not exist in the microcrystalline cellulose case. FTIR absorption spectra show that the distortion from planarity in the benzophenone molecule is larger in silicalite than in calix[6]arene, while in cellulose the distortion is slight. In spite of this, benzophenone exhibits the highest phosphorescence emission quantum yield in the case of silicalite. Benzophenone ketyl radical formation occurs with entrapment in cellulose and also with inclusion in calix[6]arene and calix[8]arene while in silicalite only triplet–triplet absorption is detected.
ISSN:	1010-6030 1873-2666
DOI:	10.1016/S1010-6030(02)00302-7