Ultrafast Light-induced Reactions

Finally, solute radical ions can be generated by light-induced, one-photon or multiphoton ionization of their parent compounds (Chaps. 5 and 16). This approach is particularly useful in the ultrafast studies of short-lived, unstable radical ions that aim to unravel their solvation, recombination, reaction, and vibrational relaxation dynamics of the primary charges (see, e.g., Chap. 10). Whereas the time scale of radiolytic production of secondary ions is always limited by the rate with which the primary species reacts with the dispersed parent molecules, light-induced charge separation can occur in <100 fsec. There are many studies on photoionization of solute molecules in liquid solutions we do not intend to review these works. 

Photochemical reductive elimination offers further examples of ultrafast light-induced reactions. Irradiation of cfr-[Ru(dmpe)2H2] with 300 nm light in cyclohexane causes elimination of H2, and rearrangement of the [Ru(dmpe)2] skeleton (dmpe— Me2P-CH2-CH2-PMe2) to the trans isomer. Interestingly, aU of those processes were reported to be completed within the instrument response time of 16 ps [100]. 

Scherzer T, Decker U. Real time FTIR-ATR spectroscopy to study the kinetics of ultrafast photopolymerization reactions induced by monochromatic UV light. Vibrational Spectroscopy. April 1999 Vol. 19(Issue 2) 385-398. 

Laser-induced fluorescence data provide a wide variety of detailed information about physical and chemical reactions. Laser-based time-resolved (picosecond) fluorescence spectroscopic techniques have been used to investigate the mechanism of photo-stabilisation by UVAs such as benzophenones, ben-zotriazoles and polymer-bound UV stabilisers [117]. Such ultrafast spectroscopic measurements can provide insight into the dynamics of the primary energy dissipation processes in polymers and polymer additives following light absorption. Excimer LIF spectra of plasticised PVC showed two distinct regions... 

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