| Popis: |
The photophysics and photochemistry of indoaniline dyes have been investigated. Absorption and fluorescence characteristics have been studied at room and liquid nitrogen temperatures. Extinction coefficients for the dyes at room temperature were found to be between 2 - 3 x 104 mol-1 dm3 cm-1 increasing to 5 - 6 x 104 mol-1 dm3 cm-1 at 77K. Fluorescence quantum yields of ~ 4 x 10-5 have been found at room temperature, but these increase by at least a factor of one hundred at 77 K. The first excited triplet state energies have been obtained using flash photolysis energy transfer methods and values of 87 to 94 kJ mol-1 determined. Nanosecond flash photolysis gives rate constants for singlet oxygen quenching by the dyes which are close to the diffusion controlled limit. Flash excitation of benzophenone has been used to photo-reduce the dyes. The reduced forms have extinction coefficients around half the value of the parent dye, and maxima to the red of the dyes. NMR and UV/vis spectrophotometry have been used to investigate the effect of acid on the dyes. This was found to be a simple protonation reaction for which pKa values of between 2.8 and 4.4 have been determined. Using the nuclear Overhauser Effect it has been found that all of the dyes studied exist in the anti configuration in their ground state. The rate of alkaline hydrolysis of the dyes has been investigated using UV/vis spectrophotometry and HPLC. The reaction is composed of two consecutive reactions. LC-MS has identified the products of the first reaction as replacement of amide groups by simple amines. The photodegradation after intense visible light irradiation was investigated and product patterns obtained using HPLC. Identification of some of the products has been possible using LC-MS. Under nitrogen the main product is the reduced form of the dye, whereas, under oxygen, products which involve the dealkylation of the tertiary amine group dominate. |
