Multi-step electron transfer in rigid photosynthetic models at low temperature: Requirements for charge separation and spin-polarized radical ion pair formation

Conference · Mon Jan 01 04:00:00 EST 1990

OSTI ID:6568109

Wasielewski, M R; Gaines, III, G L; O'Neil, M P; Svec, W A; Niemczyk, M P; Tiede, D M

Our results show that porphyrin donor-acceptor molecules possess ion pair states that are destabilized by 0.6 eV in solids relative to their energies as determined from electrochemical measurements in polar liquids. The rates of photoinduced charge separation in these molecules show a monotonic increase with increasing negative free energy of reaction in the solid state at 77 K. This information was used to design a two-step electron transfer molecule which gives a 67% yield of radical ion pair following photoexcitation. The lifetime of this radical pair is unusually long, 4 ms, and exhibits a spin-polarized EPR spectrum which suggests that the electronic coupling between the radicals within the ion pair is only about 0.001 cm{sup {minus}1}. This spin-polarized EPR spectrum is very similar to those observed previously for P{sup +} {minus} Q{sup {minus}} radical pairs produced in both green plant and bacterial photosynthetic reaction centers. It is now possible to study charge separation over fixed distances and orientations using magnetic resonance as well as optical studies. These studies will give us a direct measure of the electronic coupling between an electron donor-acceptor pair as a function of structure and environment and may lead to a better understanding of electron transfer in photosynthesis.

• Research Organization: Argonne National Lab., IL (USA)
• Sponsoring Organization: DOE/ER
• DOE Contract Number: W-31109-ENG-38
• OSTI ID: 6568109
• Report Number(s): CONF-9003209-1; ON: DE90017859
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
140505* -- Solar Energy Conversion-- Photochemical
Photobiological
& Thermochemical Conversion-- (1980-)
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
CARBOXYLIC ACIDS
CHEMICAL PREPARATION
ELECTRON TRANSFER
ENERGY LEVELS
EXCITED STATES
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
ION PAIRS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOTOSYNTHETIC REACTION CENTERS
POLARIZATION
PORPHYRINS
SYNTHESIS