Yields of excited states in the pulse radiolysis of solutions of substituted anthracenes

Abstract

A series of substituted anthracenes covering the complete range of photochemical fluorescence and triplet quantum yields, c p ~ and c p ~, have been examined in cyclohexane, benzene and dioxan solutions by pulse radiolysis. Extinction coefficients have been determined for triplet-triplet absorptions by means of Land's method and these have been used to obtain G-values for triplet states. Values for G (fluorescence) and hence G (total singlet) relative to a standard have also been measured. G (triplet) is independent of c p ~ for cyclohexane solutions, but is dependent on C ~T for benzene and dioxan. G (fluorescence) is approximately proportional to (PF, which implies constancy of G (total singlet) for a given solvent. The mechanistic implications of these findings are discussed.Divergent views have been expressed 1-4 as to the mechanism of formation of solute excited singlet and triplet states during pulse radiolysis of solutions of molecules such as naphthalene in hydrocarbon solvents, particularly cyclohexane. Two main points are at issue. The first is the extent of production of the large yield of solute triplets by inter-system crossing (I.S.C.) from solute singlet states. Direct measurements of G (fluorescence) of naphthalene in cyclohexane indicate that at some concentrations (5 x 10-3-10-2 M) over 40 % of observed triplets are formed by I.S.C. The importance of this pathway in this system is illustrated by the further observation of a 27 % enhancement of G (triplet) on saturating a 0.1 M solution with xenon.2 Nanosecond (nsec) pulse experiments with these solutions show that the triplets are formed in two stages, i.e., a '' rapid " stage complete in a few nsec and responsible for 67-90 % of the total yield, depending on solute concentration, and a "slow " stage with t+ -80 nsec. Most of the yield of triplet naphthalene produced in benzene solution is also of the " rapid " variety. " Rapid " triplets cannot be produced by

Photophysical characterization of the 9,10-disubstituted anthracene chromophore and its applications in triplet–triplet annihilation photon upconversion

“…The fitting also yielded triplet energy transfer rate constants k TET close to those determined in the Stern-Volmer analysis as well as triplet absorptivities close to half of that reported at B450 nm for 1, which is consistent with the triplet-triplet absorption spectra of 1. 71,73 The obtained values can be found in the ESI † together with the transient decays ( Fig. S21-S25, ESI †).…”

Photoprotodesilylation of 9-trimethylsilylanthracene in alcohols

“…With the additional assumption that the oscillator strength of the transition is the same for 2 and 9-MA and with ISC = 0.71 for 9-MA, one gets ISC = 0.71 × (10.67/31.56) ≈ 0.24 for 2 in MCH and 0.12 in MeOH. This assumption seems reasonably justified by the following: i) the spectroscopic properties of 9-alkylanthracenes are nearly independent of the alkyl group; 21 ii) the absorption coefficient of the "425 nm T-T transition" of anthracenes is not very sensitive to 9-alkyl substitution: the ε value for 9-MA 24 is only 10-15% lower than for anthracene and the difference induced by changing the Me substituent to SiMe 3 should be even smaller;…”

9, 10‐DICYANOANTHRACENE‐SENSITIZED PHOTOOXYGENATION OF Α,α′‐DIMETHYLSTILBENES. MECHANISM AND KINETICS OF THE COMPETING SINGLET OXYGEN AND ELECTRON TRANSFER PHOTOOXYGENATION REACTIONS

“…Using a 20 me irradiation unit, 1 me of 0 2 consumption equals a decrease of 2.23 x lop3 M of 15. Figure 2 shows the dependence of VO: ( (Kemp and Roberts, 1969). The quantum yield of intersystem crossing is correspondingly small, +isc = 0.017 (Manring et al, 1983).…”