Design, construction and optimization of a femtosecond laser spectrometer to study excited state processes.

摘要

On the femtosecond (10-15 s) and picosecond (10-12 s) time scales, seemingly instantaneous chemical processes can be observed and studied. In order to study these phenomena, the design, construction and optimization of a femtosecond laser spectrometer were undertaken. The spectrometer is composed of the transient absorption spectrometer, and the streak camera system. The transient absorption spectrometer is based upon the pump-probe technique and collects time-resolved full absorption spectra from 395 to 750 nm, with resolution down to 305 fs. Complementary to the transient absorption spectrometer is the streak camera system, which measures time-resolved emission decays at specific wavelengths. This system boasts 3.3 ps resolution with a maximum time window of 90 ns.; One of the ultrafast phenomena that has been investigated with the streak camera system is the placement and movement of pyrene and 9,10-dicyanoanthracene (DCA) molecules within the framework of faujasite X and Y zeolites. Up to two of these molecules can reside in each supercage. In the literature, there has been significant debate as to whether pyrene molecules in doubly occupied supercages exist as ground state dimers or have a dissociative ground state. In this thesis work, the rise time of pyrene excimer emission has been shown to range from 7 to 16 ps, indicating that the latter is true. DCA also exhibits an excimer emission rise time when adsorbed into Y zeolites; however, their behaviour differs from the pyrene molecules in that their rise times increase as a function of decreasing loading level. The placement of the DCA molecules and their intracavity movement have been studied by the analysis of picosecond and nanosecond fluorescence data.; Finally, the femtosecond laser spectrometer was used to study the effect of short excitation wavelength on the ultrafast photophysical behaviour of tris-(2,2'-bipyridine)ruthenium(II) derivatives. Fluorescence studies of five complexes showed that substituted bipyridine ligands exhibited an instrument response limited emission as well as a longer nanosecond emission. Transient absorption studies could not identify the species emitting the longer emission but did detect decay kinetics that were within the instrument response time of the spectrometer ( 300 fs). These results are compared to the literature and discussed.