Fredrick L. Minn

Excimer emission from dibenzofuran and substituted fluorenes

Abstract The concentration- and temperature-dependent emission quantum yields of four new excimer-forming compounds - 1-methylfluorene, 2-fluorofluorene, 2-methoxyfluorene, and dibenzofuran - were examined. The photokinetic analysis of the fluorescence data allowed approximate evaluation of the enthalpies and entropies of photoassociation, monomer-excimer equilibrium constants, and the repulsive potential energies.

Parameterization in the H2I2 potential surface

Five types of parameters were found effective in producing a reasonable semi-empirical four-electron valence-bond potential-energy surface for the H2I2 system. They were (a) the Slater exponents, (b) hybridization of the I orbital, (c) a space scale factor, (d) the I-core penetration energy, and to a more limited extent (e) the ionization potentials. Insignificant or non-physical changes in the surface resulted from alterations in (a) the integral approximations, (b) values of the electron affinities, and (c) orientation dependence of the p orbitals.

Lanthanide ions as sensitive probes. Part III. Triplet-energy transfer from 2-acetonaphthone and 2-acetylfluorene to europic ions in frozen solution

Transfer of triplet energy from 2-acetonaphthone and 2-acetylfluorene to tervalent europium ions was investigated in rigid glass by measuring the quantum yields of donor phosphorescence and acceptor fluorescence and the decay of donor emission under selective excitation of the ketone at different Eu3+ concentrations. It is suggested that transfer originates in the n,π* triplet, which is only slightly above the lowest π,π* triplet of the sensitizer. A suggested photokinetic scheme, consistent with the presumed exchange mechanism, explains the observed behaviour and yields transfer rate constants of 2·3 and 10 | mol–1 s–1 for the two sensitizers. Spectroscopic observables predicted by statistical treatments were in very good agreement with experiment and were consistent with the assumed exchange mechanism. Alterations in the predicted time-dependence of phosphorescence intensity by donor self-quenching and by changes in the microscopic decay probability expression are considered.

A new actinometer: decafluorobenzophenone–isopropyl alcohol

The clean photoreduction in propan-2-ol of decafluorobenzophenone to decafluorobenzhydrol and the ease of g.l.c. determination of the extent of conversion suggest this system as a new actinometer.

Photochemical reactions of 4,4′-di-t-butylbenzophenone in isopropyl alcohol

The photoreduction of 4,4′-di-t-butylbenzophenone in deaerated isopropyl alcohol was investigated by (a) monitoring absorption spectra following short intervals of irradiation, (b) successive determinations of absorption spectra throughout the dark period following irradiation, and (c) periodic recording of emission and excitation spectra during or after irradiation. The reactions taking place in the dark were examined separately from those during irradiation, and the second intermediate was allowed to react with sodium isopropoxide and sulphuric acid. Quantitative kinetic calculations were used to determine the orders of reaction for the individual steps and their rate constants. Extinction coefficients for the intermediates were likewise calculated, although their structures were not identified.

Lanthanide ions as sensitive probes. Part IV. Transfer of triplet energy from 2-acetylfluorene and 2-acetonaphthone to tervalent terbium in a rigid matrix

Triplet-energy transfer from 2-acetylfluorene and 2-acetonaphthone to terbic ion in rigid matrix was studied by measuring the quantum yields of donor phosphorescence and acceptor fluorescence and the decay of donor emission under selective excitation of the ketone at different TbCl3 concentrations. The bimolecular transfer rate constants derived photokinetically were an order of magnitude greater than the corresponding rate constants for transfer to Eu3+. The statistical treatment indicated that there is little separation-dependence in either transfer rate constant and suggested resonance transfer for 2-acetonaphthone–Tb3+.