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Title: Photophysics and photochemistry of pyrazolotriazole azomethine dyes
Author: Thomas, Jonathan David
Awarding Body: University of Wales, Swansea
Current Institution: Swansea University
Date of Award: 2004
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The synthesis and physical and photochemical characterisation of a series of pyrazolotriazole azomethine (PT) dyes, varying only in the substituent in the R6 position, with absorption maxima stretching from 546-633 nm, i.e. from the magenta to the cyan, has been carried out. X-ray crystallography confirms that the most stable conformer of the dyes is syn to the azomethine bond, and shows that in the solid state the dyes are planar, with zero twist angle about the azomethine bond. Singlet state studies give the extinction coefficients of the dyes to be between 5.0-6.6x104 mol-1dm3cm-1, and show quantum yields of fluorescence to be 2.0-6.3x10-4 at room temperature. At 77 K these increase to ca. 0.6-1. Singlet lifetimes have been calculated using the Strickler Berg equation and the emission quantum yields. These range from ca. 1-3.9 ps with dyes carrying strongly electron withdrawing and electron donating substituents giving longer lifetimes than those with electroneutral substituents. Using laser flash photolysis it has been found that the rate at which PT dyes isomerise from the less stable anti isomer to syn can be catalysed by the addition of acid and therefore the protonation of the azomethine bond. The rate of protonation and isomerisation is not affected by the R6 substituent (which controls dye hue) but rather by the solvent environment. Triplet energy transfer measurements from porphyrin and phthalocyanine sensitisers give the triplet energies of the PT dyes to be 88-115 kJ mol-1. singlet oxygen luminescence has measures the rate of oxygen quenching by the dyes studies to be in the range 0.13-1.89 x 108 mol-1dm3sec-1. quantum yields of fade have been found to be in the range of 0.4=11.1 x 10-6 in oxygen and 0.2-8.9x10-7 in nitrogen.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available