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Fundamental experimental and theoretical studies on the lightfastness of azo dyes. / Owen J Guy

Swansea University Author: Owen J Guy

Abstract

Photo-degradation reactions of donor acceptor azo dyes in methanol solution have been investigated. Irradiation of the second absorption band was confirmed to be the predominant cause of permanent photo-fading under anaerobic and oxygenated conditions. Under anaerobic conditions, 2'-nitro subst...

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Published: 2001
Institution: Swansea University
Degree level: Doctoral
Degree name: Ph.D
URI: https://cronfa.swan.ac.uk/Record/cronfa42255
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last_indexed 2018-08-03T10:09:40Z
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spelling 2018-08-02T16:24:28.5889881 v2 42255 2018-08-02 Fundamental experimental and theoretical studies on the lightfastness of azo dyes. 73fc2c90a661b323d59b2e42794898d7 NULL Owen J Guy Owen J Guy true true 2018-08-02 Photo-degradation reactions of donor acceptor azo dyes in methanol solution have been investigated. Irradiation of the second absorption band was confirmed to be the predominant cause of permanent photo-fading under anaerobic and oxygenated conditions. Under anaerobic conditions, 2'-nitro substituted azobenzenes and azothiophene dyes were the least lightfast, with half-lives of under one hour, whilst 4'-nitro substituted dyes had half-lives of between 1 and 1.5 hours. Photo-degradation was retarded in the presence of oxygen by between 4 and 16 times relative to fading under anaerobic conditions. The photo-fading of dyes deposited on various substrates exhibited similar behaviour to dyes in methanol solution. UV/visible spectra showed that 2'-nitro substituted dyes underwent complete loss of intensity of the visible absorption peak and a corresponding increase in the absorption in the UV region of the spectrum when irradiated under anaerobic conditions, indicating cleavage at the azo bridge and subsequent formation of mono-phenyl derivatives. In contrast, under oxygenated conditions, a gradual loss of intensity at the visible absorption maximum was observed, with no notable newly formed peaks are detected in the UV region suggesting that cleavage at the azo bridge is less significant. The photoproducts of the reaction are suggested to include the reduced form of azo dyes containing nitro groups. Theoretical semi-empirical AMI and ab initio calculations using the 3-21G basis set, predicted reasonable structures for the ground states of dyes. Spectroscopic calculations using a version of the CNDO/S method gave good correlations between calculated transition energies and experimental data obtained in cyclohexane. The results of a multi electron configuration interaction treatment of AMI structures in the gas phase were inconsistent with experimental spectral data obtained in cyclohexane but improved correlations were obtained between calculated transition energies and experimental data in methanol. The structures and energies of excited singlet and triplet states have also been calculated by the AMI method but no apparent correlation of these energies with the lightfastness of azo dyes could be identified. A tentative relationship between calculated distributions of the unpaired electrons in the second excited triplet state and the site of reactivity in the dyes was proposed. E-Thesis Organic chemistry.;Physical chemistry. 31 12 2001 2001-12-31 COLLEGE NANME Chemistry COLLEGE CODE Swansea University Doctoral Ph.D 2018-08-02T16:24:28.5889881 2018-08-02T16:24:28.5889881 Faculty of Science and Engineering School of Engineering and Applied Sciences - Chemistry Owen J Guy NULL 1 0042255-02082018162440.pdf 10797963.pdf 2018-08-02T16:24:40.1500000 Output 37942819 application/pdf E-Thesis true 2018-08-02T16:24:40.1500000 false
title Fundamental experimental and theoretical studies on the lightfastness of azo dyes.
spellingShingle Fundamental experimental and theoretical studies on the lightfastness of azo dyes.
Owen J Guy
title_short Fundamental experimental and theoretical studies on the lightfastness of azo dyes.
title_full Fundamental experimental and theoretical studies on the lightfastness of azo dyes.
title_fullStr Fundamental experimental and theoretical studies on the lightfastness of azo dyes.
title_full_unstemmed Fundamental experimental and theoretical studies on the lightfastness of azo dyes.
title_sort Fundamental experimental and theoretical studies on the lightfastness of azo dyes.
author_id_str_mv 73fc2c90a661b323d59b2e42794898d7
author_id_fullname_str_mv 73fc2c90a661b323d59b2e42794898d7_***_Owen J Guy
author Owen J Guy
author2 Owen J Guy
format E-Thesis
publishDate 2001
institution Swansea University
college_str Faculty of Science and Engineering
hierarchytype
hierarchy_top_id facultyofscienceandengineering
hierarchy_top_title Faculty of Science and Engineering
hierarchy_parent_id facultyofscienceandengineering
hierarchy_parent_title Faculty of Science and Engineering
department_str School of Engineering and Applied Sciences - Chemistry{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Engineering and Applied Sciences - Chemistry
document_store_str 1
active_str 0
description Photo-degradation reactions of donor acceptor azo dyes in methanol solution have been investigated. Irradiation of the second absorption band was confirmed to be the predominant cause of permanent photo-fading under anaerobic and oxygenated conditions. Under anaerobic conditions, 2'-nitro substituted azobenzenes and azothiophene dyes were the least lightfast, with half-lives of under one hour, whilst 4'-nitro substituted dyes had half-lives of between 1 and 1.5 hours. Photo-degradation was retarded in the presence of oxygen by between 4 and 16 times relative to fading under anaerobic conditions. The photo-fading of dyes deposited on various substrates exhibited similar behaviour to dyes in methanol solution. UV/visible spectra showed that 2'-nitro substituted dyes underwent complete loss of intensity of the visible absorption peak and a corresponding increase in the absorption in the UV region of the spectrum when irradiated under anaerobic conditions, indicating cleavage at the azo bridge and subsequent formation of mono-phenyl derivatives. In contrast, under oxygenated conditions, a gradual loss of intensity at the visible absorption maximum was observed, with no notable newly formed peaks are detected in the UV region suggesting that cleavage at the azo bridge is less significant. The photoproducts of the reaction are suggested to include the reduced form of azo dyes containing nitro groups. Theoretical semi-empirical AMI and ab initio calculations using the 3-21G basis set, predicted reasonable structures for the ground states of dyes. Spectroscopic calculations using a version of the CNDO/S method gave good correlations between calculated transition energies and experimental data obtained in cyclohexane. The results of a multi electron configuration interaction treatment of AMI structures in the gas phase were inconsistent with experimental spectral data obtained in cyclohexane but improved correlations were obtained between calculated transition energies and experimental data in methanol. The structures and energies of excited singlet and triplet states have also been calculated by the AMI method but no apparent correlation of these energies with the lightfastness of azo dyes could be identified. A tentative relationship between calculated distributions of the unpaired electrons in the second excited triplet state and the site of reactivity in the dyes was proposed.
published_date 2001-12-31T03:52:36Z
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score 11.012678

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