Acetone, triplet

Further detailed information on the reactive excited states of p. -unsaturated ketones has been acquired with (3a-c). Inefficient intersystem crossing from the singlet to the triplet state precedes population of Tz(.n,Tt ) from which the 1,3-acyl shift, induced by Norrish type I cleavage, occurs more readily than internal conversion to Ti Ti has been estimated to lie within 8 W mol of the acetone triplet (335 kJ mol ). That the 1,3-acyl shift is coupled not only with singlet-state but also Tz-state reactivity has been unequivocally shown by two methods. Thermal decomposition of a dioxetane, a derivative of (3a), generates predominantly the T2 state from which the 1,3-acyl shift product is formed concurrently with the ODPM products (4a) and (5a) via A photo-CIDNP study has independently demon-... 

Also a number of photosensitized decompositions of dioxetanes have been reported. Thus, Barron and Turro11 showed that dioxetane lb is dissociated by pyrene singlets into 30% acetone triplets, determined by cis-trans isomerization of crotononitrile. Also biacetyl triplets sensitize the decomposition of lb, which was used in an ingenious way by Turro and Lechtken119 to promote the Norrish type II cleavage of butyrophenone. The sequence of events in this ternary system is illustrated in Eq. (47). 

TABLE n. Inorganic Anions Absolute Rate Constants for Quenching of 02 (k ) and Acetone Triplet (kg) and Stern-Volmer Constants for Quenching of Fluorescence of Methylene Blue (Kjy-.NB) and Rose Bengal (Ksv RB)... 

Optical Emission Spectra Acetone Triplet in Aqueous Solution... 

Table 11.4 Geometric Parameters of Acetone Triplet (ActT) and Singlet Ground State (ActGS) in Aqueous Solution Issuing from Gas-Phase Optimizations and GLOB Simulations...

The effect of biacetyl was best documented in the case of acetone (Heick-Icn and Noyes, 1959). It was shown that a pressure of 0.5 mm biacetyl is sufficient to quench all acetone phosphorescence but that acetone fluorescence remains constant as biacetyl pressure is increased to 5 mm. Thus, in this case biacetyl serves only as an acceptor of triplet excitation, and the observed decrease in the quantum yield of primary decomposition of acetone could be attributed to deexcitation of acetone triplets prior to dissociation. 

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