THE EVALUATION AND CHARACTERIZATION OF "SLOW" INTERFERENCES IN THE MODULATED GAIN SPECTROMETER
Abstract
In an attempt to more fully understand the observed output from the modulated gain spectrometer, we have undertaken the mathematical analysis of both the photophysical interactions responsible for the signal and the electronics which are employed in the collection process. The results obtained from this analysis are used to develop numerical routines for the computation of the expected output for a given set of molecular parameters. The first approach presented, employs a finite difference algorithm to compute the time dependent response of the specified model to the pumping pulse train. The second approach uses the Fourier transform convolution theorem and a fast Fourier transform subroutine to prepare the individual excited state concentration profiles through sequential convolutions and scaling. The routines have been used in the characterization of the interactions of rhodamine 6G and iodide. When the fluorescence lifetimes of a series of mixtures were measured, the data did not follow the normal quenching trends, but, indicated the presence of a second absorbing species. Kinetic analysis of the system indicated that a triplet excited state complex (exciplex) might be the cause of the additional signal. The ability to measure the spectral properties of very long-lived species with the modulated gain spectrometer was examined both experimentally and with the kinetic modeling routines. The compounds 3,3'-diethyloxadicarbocyanine iodide (DODCI) and 3,3'-diethylthiadicarbocyanine iodide (DTDCI) were suggested as instrument alignment standards due to the intense, relatively flat time-resolved gain signal produced.
Degree
Ph.D.
Subject Area
Analytical chemistry
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