Quenching and Sensitization Processes

Vogtle F, Gestermann S, Kauffmann C et al (1999) Polypropylene amine) dendrimers with peripheral dansyl units protonation, absorption spectra, photophysical properties, intraden-drimer quenching, and sensitization processes. J Am Chem Soc 121 12161-12166... 

Intramolecular quenching and sensitization processes have also been investigated with nonconjugated covalently linked organometallic compounds such as the blchromophoric "double porphyrins" [13] (260). From a study of the emission characteristics of these double porphyrins the following conclusions were... 

Quenching and sensitization processes 4.1 EXCITED STATE QUENCHING... 

Balzani, V Moggi, L. Manfrin, M. F Bolletta, M. F Laurence, G. S. Quenching and Sensitization Processes of Coordination Compounds, Coord. Chem. Revs. 1975,15, 321. 

In this section we deal with quantitative steady-state luminescence intensity determination in solution, at a fixed emission wavelength, using a commercial spectrofluorimeter with right-angle excitation (perpendicular geometry). These kind of measurements are particularly important in analyte detection, titrations, quenching and sensitization experiments, photoreaction and photoluminescence quantum yield determination, and whenever a luminescence signal is used to monitor a chemical process. 

A significant proportion of the fine chemicals are complex, multifunctional large molecules. These molecules are labile, unstable at elevated temperature, and sensitive towards (occasionally even minor) changes in their environment (e.g. pH). Therefore, processes are needed with inherent protective measures (e.g. chemical or physical quenching) or a precise control system to operate exactly within the allowable range. Otherwise the yield of the desired product can drop to nearly zero. 

The commercialization of inexpensive robust LED and laser diode sources down to the uv region (370 nm) and cheaper fast electronics has boosted the application of luminescence lifetime-based sensors, using both the pump-and-probe and phase-sensitive techniques. The latter has found wider application in marketed optosensors since cheaper and more simple acquisition and data processing electronics are required due to the limited bandwidth of the sinusoidal tone(s) used for the luminophore excitation. Advantages of luminescence lifetime sensing also include the linearity of the Stem-Volmer plot, regardless the static or dynamic nature of the quenching mechanism (equation 10) ... 

Indirect evidence for the formation of a complex intermediate in diffusional energy transfer processes may be provided by the measurement of kt from both donor quenching and acceptor sensitization at low temperatures where kQC kf = 1/T° in this case exciplex relaxation should reduce the quencher sensitization efficiency but leave the donor fluorescence quenching constant unchanged. 

The mercury sensitized emission, (process (b)) from TI and Na vapour has been discussed in Section 6.6.6. The quenching to 63P0 (process (d)) by CO, N2 and N O, NH3 are presented in Section 6.2. In presence of H2, the possible photochemical reactions are... 

The sensitization of semiconductors is a special example of electron transfer quenching and may prove to be very important. A photoexcited electron may, for example, be injected with high quantum yield into the semiconductor conduction band, to produce a photovoltaic device. The hole that is left behind may then perform some useful oxidation process. 

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