Photochemical coal dissolution. Quarterly technical progress report, January 1--March 31, 1996

As mentioned in the report on the previous quarter, the authors have turned their attention to studies of photochemically-induced-charge-transfer phenomena involving aromatic electron donors. Coal is a porous material and it has been demonstrated that there are ground-state charge-transfer-interactions between imbibed TCNE or TCNQ and the automatic systems in bituminous coals. The authors aim to develop a preliminary understanding of the ground and excited state donor-acceptor interactions and the charge-transfer phenomena in porous materials that are better-defined than coals. They are performing background examinations of a set of donors and acceptors in solution by cyclic voltammetry and uv-visible spectroscopy. These preliminary experiments are being followed by systematic studies of the adsorption of the donors and acceptors, individually and together into adjacent supercages of a series of cation-exchanged X- and Y-type faujasite zeolites. Ultraviolet-irradiation of these systems are being performed and electron paramagnetic resonance examination of the samples is being made for the presence of paramagnetic, one-electron, charge-transfer products. In related work performed by students supported by this contract, the authors have reached a good understanding of the interactions and molecular motions of free radical {pi} electron systems in the X- and Y-type faujasite zeolites. Luminescence spectroscopy may also be used to examine the doped zeolite samples in future experiments. The authors have begun to examine the donor-acceptor pairs: diphenylamine-benzophenone, nitroxyl and substituted nitroxyl radical-benzophenone, and aromatic hydrocarbon-unsaturated tetracyano hydrocarbon. The oxidation and reduction potentials and excitation energies of these systems are given. The aromatic hydrocarbon donors span the range of typical aromatic ring sizes found in bituminous, subbituminous and lignite coals