| dc.description.abstract | Electrochemiluminiscence, (ECL), is an electrochemically-induced process that leads to the generation of measurable luminescent signals at the electrode surface. The luminescent signals occur when electrochemically generated intermediates undergo a highly exergonic reaction to produce an electronically excited state that then emits light. Immobilization of the ECL luminophore on an electrode surface provides
enhancement of ECL intensity. This work presents results of the feasibility study focused on the application of novel luminophores for electrochemiluminescence (ECL) sensors. The thesis mainly focuses on studying the ECL of polyanilinorutheniumbipyridyl- imidazo phenanthroline and carboxydifluoroboradiazaindancence luminophores. The influence of the synthetic methods on the electrochemical, structural and photophysical properties of poly(8-anilino-lnaphthalene sulphonic acid) (P ANSA) synthesized by electropolymerization
(PANSA) and chemical polymerization (PANSA) were studied. Cyclic voltammetry (CV) data revealed that the electrogenerated PANSA contains species of mixed redox states; with evidence of the presence of penigraniline, emeraldine and leucoemeraldine forms of PANSA. In contrast, the CV of PANSA indicated that it is predominantly in the emeraldine form with a reduction potential at approximately + 0.2 V. The presence of emeraldine moiety in PANSA was confirmed from UV-Vis spectroscopy data. A band gap energy value of 2.5 eV was calculated for the emeraldine in PANSA from the UV data. Comparative study of the charge transfer coefficient, DCT, of the two types of PANSA indicated moderate charge propagation in PANSA (DCT = 1.68 ± 0.1 x 10-8 cm2 s-') which was order of magnitude lower than for PANSA (DCT = 1.68 ± 0.3 x 10-7 cm2 s-'). The differences in the structural properties of the two polymers were reflected in their IR spectra, with evidence of
C=C and C=N stretching vibrations observed at 2030, 2158 and 2486 cm-I in PANSA, which are absent in PANSA. The mode of synthesis had a modest impact on the photophysics of the polymers, for example PANSA exhibited a luminescent lifetime of9.00 ± 0.05 ns compared with 11.5 ± 0.07 ns for PANSA. However, time resolved emission anisotropy studies gave a rotational correlation time, p, of 13.8 ± 2.47 ns for PANSA compared to 0.633 ± 0.03 ns for its chemically generated analogue. This suggests a much shorter chain length in the PANSA molecule and higher cross-linking or aggregation in PANSA that can limit incorporation of ruthenium complex on the polymer backbone. As a result, electrochemiluminescent films have been formed by electrodepositing polyaniline, PANI, films in the presence of [Ru(bpY)2PIC]2+; bpy is 2,2'-bipyridyl and PIC is (2,2'-bipyridyl)-2( 4- carboxylphenyl) imidazo [4,5 ][ 1,10] phenanthroline in this work. The homogeneous charge transport diffusion coefficient, DCT, for the Ru2+/3+couple within the PANI film is 2.6 ± 0.9 x 10-10 cm2s-l. The large DCT facilitates a fast regeneration of Ru3+and, coupled to a relatively rigid microenvironment, results in a high ECL intensity in the presence oftripropylamine as co-reactant compared to [Ru(bpY)3f+. Significantly, despite the conducting nature of the polymer backbone, the [Ru(bpy)2PICH2]2+ loaded
PANI has the highest efficiency, 1.00%, yet reported for a surface confined ruthenium complex. PANI-Ru complex showed to have many properties that make it an ideal luminophore for sensitive and selective analytical methods; however, it would be useful to have other ECL labels that can span a wide range of wavelengths so that simultaneous determination of several analytes in a single sample can be investigated. In this case, the photophysics, electrochemical and electrochemiluminescent properties of a novel 1,3,5,7 -tetramethyl-8-[ (2-fluorophenyl)-6-methoxy-l ,5-naphthyridine-3-carboxy ]-4,4'difluoroboradiazaindace-ne BODIPY -COOH, dye were demonstrated in this work. The photophysics studies revealed that BODIPY -COOH is highly luminescent: exhibiting sharp absorbance bands, intense emission bands and
high emission quantum yield. The quantum yield proved to be solvent dependent and was determined to be 0.88 ± 0.02 and 0.60 ± 0.04 in dimethylsulphoxide (DMSO) and acetonitrile (MeCN), respectively. Electrochemiluminescence (ECL) of BODIPYCOOH in solution was generated in the presence of either benzoyl peroxide (BPO) or hydrogen peroxide. The ECL turn-on potential in the presence of BPO was observed at potentials that are greater than - 1.5 V, and when H202 was used the ECL turn-on potential was significantly fine-tuned to less negative potential of - 0.4 V. Electrochemiluminescent thin films of BODIPY -COOH on Pt electrodes exhibited luminescence properties similar to those of the free dye in solution. However, the solution based approach ECL has its own limitations such as loss of signal due to the
diffusion of the ECL reagent out of the detection zone. To overcome loss of signal effects, the introduction of cysteamine and cysteine linkers to the BODIPY dye were employed. It was seen that self-quenching was not sufficient to interfere significantly with the film ECL emission properties and thus the BODIPY thin film can be used in ECL applications. Interestingly, the BODIPY film exhibited the strongest
luminescence in water and this is potentially useful in ECL application in biological media. | en_US |
