ROOM TEMPERATURE PHOSPHORESCENCE OF AMINOBENZOIC ACIDS (RTP, FLUORESCENCE, NONEXPONENTIAL DECAY)
A laboratory constructed Room Temperature Phosphorescence Lifetime Spectrophotometer (RTPLS) is described. This instrument was used to measure RTP intensities and lifetimes both for single component decays and for multicomponent decays. Careful blank subtraction facilitated by a reproducible chopped-xenon arc source and data reduction using the non-linear least squares method are major features of the RTPLS. The performance and limitations of the RTPLS are evaluated. Better than 2% RSD was attained for multiple determinations of a single sample. A ratio between two lifetimes exceeding 1:2.5 and a lifetime no less than 0.5 ms are the limits for the good results. The RTP of the three isomeric aminobenzoic acids adsorbed on filter paper was studied in detail as a function of many parameters. Alkali halides added to the matrix as external heavy atoms enhanced RTP. As expected, RTP intensities increased with the atomic numbers of the heavy atoms. Positions of the substituents on the aromatic ring of the compounds and the alkali ions associated with halide ions also play an important role in these photophysical processes. The emission decays of the isomeric acids in the presence of heavy atoms exhibited a nonexponential decay characteristic. These decays were resolved into two lifetimes; the short-lived component, with lifetime less than 10 ms is insensitive to the perturber concentration while the long-lived component is markedly affected. The lifetime ratio is about 1:7 at 5.0 x 10('-3) M concentration of sample and 1.0 M concentration of alkali iodide. Exciplex formation between the excited molecule and the perturber in the ground state is the proposed mechanism that accounts for the external heavy atom effect, but direct spin-orbit coupling involvement also plays an important role in RTP enhancement. A mathematical description of the proposed mechanism fits very well with the experimental results obtained in this study.
"ROOM TEMPERATURE PHOSPHORESCENCE OF AMINOBENZOIC ACIDS (RTP, FLUORESCENCE, NONEXPONENTIAL DECAY)"
(January 1, 1985).
Dissertations (1962 - 2010) Access via Proquest Digital Dissertations.