Sensitized photoreduction of bis(acetylacetonato)nickel(II) by triplet-state aromatic ketones.

摘要: Bis(acetylacetonato)nickel(II), Ni(acac),, quenched triplet state aromatic ketones with high efficiency but only certain energy levels successfully sensitized the photoreduction of Ni(acac)* to give acetylacetone radical and Ni(1) complexes. A short-lived species was detected by ESR UV spectroscopy, acetylacetonyl trapped 2-nitroso-2-methylpropane or phenyl-tert-butylnitrone as a stable nitroxide H atom donors acetylacetone. The transient complexes decayed either first-order second-order kinetics, depending on concentrations, Ni(0) ferromagnetic colloidal nickel. occurs if trapped. Various evidence suggested that quenching mechanism not likely occur transfer best interpreted involve partial charge within an excited-state complex. in complex undergoes hydrogen abstraction from solvent competition reverse electron transfer. quantum is attributed extent charge-transfer contribution donating ability solvents. It also confirmed ketyl derived responsible for reduction Ni(acac)2. In solution, transition-metal cations quench excited states hydrocarbons efficiencyz-8 have been shown be potential "ultraviolet stabilizers" polymers recent years.& deactivation electronically has studied ex- tensively kinetic flash photolysis?" investigations which lead variety proposals. early investigations, Hammond's group3 observed P-diketonates compounds similar rate constants range IO9 M-' s-l regardless levels.3 Porter's groupZ pioneered inves- tigations this area found efficient paramagnetic such oxygen, nitrogen oxides, metal ions, catalyzed intersystem crossing mechanism, nature expanded along allowed spin exchange93l0 (eq 1) charge-transfer2.6Jo *A + B - (A*--B?) reaction (1) (2)