TWO-PHOTON EXCITATION SPECTROSCOPY: I. DEVELOPMENT OF A TWO COLOR SPECTROMETER BASED ON RING DYE LASERS. II. INVESTIGATIONS OF METAL CHELATE COMPLEXES
Abstract
The two-photon absorption process accesses electronic states of molecules which are fobidden in conventional absorption spectroscopy. This aspect of the process is exploited in the investigation of the gerade d(--->)d* bands of metal chelate complexes via two-photon excitation of luminescence. A versatile dual laser two-photon excitation spectrometer is developed in order to meet the requirements of metal chelate investigations. The excitation source is based on two synchronously-pumped delay line ring dye lasers. The lasers are evaluated in terms of picosecond pulse optimization parameters and cross-absorption stability. Three possible configurations of the source are developed and described. These include single beam, double beam, and frequency doubling, thus allowing two-photon or single-photon excitation of the sample as well as complete two-photon polarization studies in fluids. Signal detection is an important consideration in two-photon excitation, since absorption cross-sections are low. Also, because of signal errors due to source characteristics, data must be evaluated using a reference correction scheme. For generating absolute two-photon spectra, signal reference correction equations and techniques are described. A discussion of the signal evaluation procedure for cases of linear signal contribution is presented. Equations and techniques of the cross-absorption two-photon experiment are discussed. The partial return of laser radiation into the resonator due to diffuse reflection has the potential of disrupting the pulse train and reducing the stability of the experiment. This feedback effect is investigated in the actively mode-locked argon laser and synchronously-pumped dye laser, and techniques for preventing the effect are discussed. Two-photon spectra of cis-dicyanobis-(4,4'-dimethyl-2,2'-bipyridine)rhodium(III) and cis-dicyanobis-(3,4,7,8-tetramethyl-1,10-phenanthroline)rhodium(III) are presented. These spectra represent the first report of two-photon excitation of metal chelates dissolved in vitreous solvents.
Degree
Ph.D.
Subject Area
Chemistry
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