The interaction between the excited triplet state of ketones and olefins: the role of triplet exciplexes

Abstract

The quenching of triplet acctone in degassed acetorlitrile solution by electron-rich and electron-deficient olefins has been measured by Rash emission technique. With the exception of fumaronitrile, the efficiency of quenching of triplet ketones by olefins is not determined by the triplet energy of the ketone, but by the ability of the excited ketone to donate or accept electrons. The results are consistent with the assu~nption that back dissociation of the triplet exciplex is an important process in the overall reaction and accounts for quenching rate constants which are less than those for diffusion-controlled reactions. Lifetimes and binding energies of the triplet exciplexes have been estin~ated.

Triplet energies of fumaronitrile and maleonitrile

“…The quenching rates for these sensitizers are higher than the nonelectron donating sensitizers with the same or even higher E,'S. Such phenomenon has also been observed earlier by other workers (6,7). The faster quenching rates are probably due to charge-transfer from the excited donors (sensitizers) to the ground state acceptors.…”

Electronic to vibrational energy conversion and charge transfer contributions during quenching by molecular oxygen of electronically excited triplet statesDedicated to Professor Frank Wilkinson on the occasion of his retirement.

“…These values can be compared with an expected slope of À0.178 mol kJ À1 for reactions involving complete electron transfer. [36][37][38] The plots shown in Fig. 4, using our measured values of the half wave oxidation potentials and triplet energies of the substituted naphthalenes reported recently by Schmidt et al, 16 show far less scatter than those reported previously by ourselves.…”

Quenching of the fluorescence of substituted benzenes by halomethanes

“…3. That the point for CFCl, falls far off the line et al (15) for the quenching of triplet acetone by olefins and is not surprising since widely divergent values for E A of this -6 eV-' given by Saperstein and Levin (5) for the quenching molecule are given in the literature (5, 13, 14). It is also of singlet aromatics by chloroform.…”