Magnetic field effects on the intra- and intermolecular exciplex fluorescence of phenanthrene and dimethylaniline

Abstract

As noted earlier, the equilibrium between FeDTPA2" and FeDTPA-OFI3" is slow and, therefore, it is unlikely that normal ligand exchange is involved. It is known that Fem can expand its coordination sphere from 6 to 7 and we might speculate that OH" occupies a coordination site that is otherwise available for attack by the DTPA radical.As pointed out previously, on the time scale of the experiment the DTPA radical has not quantitatively converted to its final form (generally considered as a methylene radical of an acetate group). However, it seems likely that we are dealing with a carbon-centered radical as the final form of the transient metal adduct, LFelnDTPAf*. Our data suggests a mechanism that involves an association, K6 -2.2 X 104 M"1 *, followed by a fast rearrangement, ki = 2.1 X 104 s"1, to a more stable form of the intermediate. The rate of reaction 7 excludes substitution processes but may be consistent with isomerization or tautomerization of the bound radical to its more stable form, albeit at a slightly higher rate than that of the corresponding process of the free DTPA radical (=H03 s"1).Decay of this species, LFemDTPAf", under all conditions that were experimentally accessible, involved a bimolecular reaction with excess FeDTPA2", indicating that the radical form liganded to the iron is insufficiently reducing to decay by intramolecular oxidation-reduction. The catalytic effect of a second FeDTPA2" on ligand oxidation may be analogous to that observed in other systems such as Cu"NTA.

Time-Resolved Magnetic Field Effects Distinguish Loose Ion Pairs from Exciplexes

“…29,30,54,55,58,63−65 In contrast to that, many studies focusing predominantly on photochemical aspects can be found, suggesting that the exciplex is the initial quenching product even at fairly high permittivities. 28,57,66,67 …”

Electric Field Effects on Fluorescence of Methylene-Linked Compounds of Phenanthrene andN,N-Dimethylaniline in a Poly(methyl methacrylate) Polymer Film

“…As the concentration increases, the magnitude of the field-induced quenching of the LE fluorescence becomes larger, indicating that the intermolecular PIET from DMA to the excited state of PHE is also enhanced by F. The field effect on the intermolecular PIET is also considered to result from the field-induced change in free energy gap. Both the PIET rate ∆I F (ν) ) (fF) 2 C ) (∆µ) 2 [5 +(3 cos 2 -1)(3 cos 2 -1)]/(30h 2 c 2 ) (8) ∆µ ) |∆µ|; ∆R j ) ( 1 / 3 )Tr(∆r) (9) and its field-induced change increase exponentially, as the donor-acceptor distance decreases. It is considered that a radical ion pair is produced following PIET, and then the fluorescent exciplex is produced.…”

“…6,9 Phenanthrene chromophores act as an electron acceptor (A), and N,N-dimethylaniline chromophores act as a donor (D) in PIET. 16 Samples for the measurements of the electric field effects on absorption and emission spectra were prepared in the same manner as reported elsewhere.…”

Magnetic field effects upon photochemistry of bichromophoric chain molecules containing nitroaromatic and arylamino moieties: Elucidation of reaction mechanism and control of reaction yields

“…The charge-separated biradical formed after photoexcitation in benzene can be characterized as an exciplex or a contact ion pair (18) and, therefore, the interradical distance must be very small. The observation of pronounced magnetic field effects suggests a large separation (21 nm) between the two unpaired electrons (3,15). It is reasonable to assume a neutral biradical as a reaction intermediate in benzene.…”