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Surface Photochemistry: 3,3'-Dialkylthia and Selenocarbocyanine Dyes Adsorbed onto Microcrystalline Cellulose
Molecular Physical Chemistry Center, and IN-Institute of Nanoscience and Nanotechnology, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
School of Technology and Business, Polytechnic Institute of Portalegre, Lugar da Abadessa, Apt 148, 7301-901 Portalegre, Portugal
CICS - Health Sciences Research Center, Beira Interior University, Av. Infante D. Henrique, 6200-506 Covilhã, Portugal
Department of Chemistry and Chemistry Center, Trás-os-Montes e Alto Douro University, Apartado 1013, 5001-801 Vila Real, Portugal
* Author to whom correspondence should be addressed.
Received: 12 December 2011; in revised form: 29 December 2011 / Accepted: 29 December 2011 / Published: 9 January 2012
Abstract: In this work, thia and selenocarbocyanines with n-alkyl chains of different length, namely with methyl, ethyl, propyl, hexyl and decyl substituents, were studied in homogeneous and heterogeneous media for comparison purposes. For both carbocyanine dyes adsorbed onto microcrystalline cellulose, a remarkable increase in the fluorescence quantum yields and lifetimes were detected, when compared with solution. Contrary to the solution behaviour, where the increase in the n-alkyl chains length increases to a certain extent the fluorescence emission FF and τF, on powdered solid samples a decrease of FF and τF was observed. The use of an integrating sphere enabled us to obtain absolute FF’s for all the powdered samples. The main difference for liquid homogeneous samples is that the increase of the alkyl chain strongly decreases the FF values, both for thiacarbocyanines and selenocarbocyanines. A lifetime distribution analysis for the fluorescence of these dyes adsorbed onto microcrystalline cellulose, evidenced location on the ordered and crystalline part of the substrate, as well as on the more disordered region where the lifetime is smaller. The increase of the n-alkyl chains length decreases the photoisomer emission for the dyes adsorbed onto microcrystalline cellulose, as detected for high fluences of the laser excitation, for most samples.
Keywords: surfaces and nanocavities; thia and selenocarbocyanine dyes; lifetime distribution analysis; absolute quantum yields of fluorescence emission; singlet oxygen formation quantum yield
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Vieira Ferreira, L.F.; Ferreira, D.P.; Duarte, P.; Oliveira, A.S.; Torres, E.; Ferreira Machado, I.; Almeida, P.; Reis, L.V.; Santos, P.F. Surface Photochemistry: 3,3'-Dialkylthia and Selenocarbocyanine Dyes Adsorbed onto Microcrystalline Cellulose. Int. J. Mol. Sci. 2012, 13, 596-611.
Vieira Ferreira LF, Ferreira DP, Duarte P, Oliveira AS, Torres E, Ferreira Machado I, Almeida P, Reis LV, Santos PF. Surface Photochemistry: 3,3'-Dialkylthia and Selenocarbocyanine Dyes Adsorbed onto Microcrystalline Cellulose. International Journal of Molecular Sciences. 2012; 13(1):596-611.
Vieira Ferreira, Luís F.; Ferreira, Diana P.; Duarte, Paulo; Oliveira, A. S.; Torres, E.; Ferreira Machado, I.; Almeida, P.; Reis, Lucinda V.; Santos, Paulo F. 2012. "Surface Photochemistry: 3,3'-Dialkylthia and Selenocarbocyanine Dyes Adsorbed onto Microcrystalline Cellulose." Int. J. Mol. Sci. 13, no. 1: 596-611.