Transient absorption spectroscopy has been used to probe the electron injection dynamics of transition metal polypyridyl complexes adsorbed onto nanocrystalline TiO 2 photoelectrodes. Experiments were performed on photoelectrodes coated with Ru(H 2 L′) 2 (CN) 2 , Os(H 2 L′) 2 (CN) 2 , Ru(H 2 L′) 2 (NCS) 2 , or Os(H 2 L′) 2 (NCS) 2 , where H 2 L′ is 4,4′-dicarboxylic acid-2,2′-bipyridine, to study how the excited-state energetics and the nature of the metal center affect the injection kinetics. All of these complexes exhibited electron injection dynamics on both the femtosecond and picosecond time scales. The femtosecond components were instrument-limited (<200 fs), whereas the picosecond components ranged from 3.3 ( 0.3 ps to 14 ( 4 ps (electron injection rate constants k 2 ′ ) (7.1-30) × 10 10 s -1). The picosecond decay component became more rapid as the formal excited-state reduction potential of the complex became more negative. Variable excitation wavelength studies suggest that femtosecond injection is characteristic of the nonthermalized singlet metal-to-ligand chargetransfer ( 1 MLCT) excited state, whereas picosecond injection originates from the lowest-energy 3 MLCT excited state. On the basis of these assignments, the smaller relative amplitude of the picosecond component for the Ru sensitizers suggests that electron injection from nonthermalized excited states competes more effectively with 1 MLCT f 3 MLCT conversion for the Ru sensitizers than for the Os sensitizers.

Reaction rates extracted from measurements of donor luminescence quenching by randomly dispersed electron acceptors reveal an exponential decay constant of 1.23 per angstrom for electron tunneling through a frozen toluene glass (with a barrier to tunneling of 1.4 electron volts). The decay constant is 1.62 per angstrom (the barrier, 2.6 electron volts) in a frozen 2-methyl-tetrahydrofuran glass. Comparison to decay constants for tunneling across covalently linked xylyl (0.76 per angstrom) and alkyl (1.0 per angstrom) bridges leads to the conclusion that tunneling between solvent molecules separated by approximately 2 angstroms (van der Waals contact) is 20 to 50 times slower than tunneling through a comparable length of a covalently bonded bridge. Our results provide experimental confirmation that covalently bonded pathways can facilitate electron flow through folded polypeptide structures.

We have shown that Ru II (bpy) 2 (bpy-4-(xylyl) x -≡-phenyl-COOH)(PF 6 ) 2 (abbreviated Rux, where x ) 0, 1 or 2 xylyl groups; bpy ) 2,2′-bipyridine) dyes can act as sensitizers for nanocrystalline TiO 2 in functional photoelectrochemical cells under simulated solar illumination, albeit with low efficiencies. Both the shortcircuit photocurrent density and the open-circuit voltage decreased as x was increased. Electron injection (10 6 -10 8 s -1 ) was slightly faster for the x ) 0 dye, but both recombination (10 -15 -10 -13 cm 3 s -1 ) and regeneration (10 4 -10 6 s -1 for 10 mM I -) were slightly faster for the x ) 2 dye. We suggest that the lack of distance dependence is due to the flexible one-carboxyl attachment to the surface resulting in the Ru-TiO 2 electron-tunneling distance being very similar for x ) 0, 1, and 2. For all of the Rux sensitizers, a relatively small potential was needed for generation of current in the dark, indicating that the reaction between electrons in TiO 2 and the I 3 -/Ielectrolyte solution is as favorable for the Rux sensitizers as for unmodified TiO 2 electrodes.

S-1: Determining Thermodynamic Parameters for Isomer EquilibrationTo determine the thermodynamic parameters for the equilibrium between the two isomers, absorption spectra at various temperatures are deconvoluted and the oscillator strengths 1 (which are proportional to the area under the curve for each absorption band) are determined. In order to properly describe the absorption spectra of Ir 2 (dimen) 4 2+ over the entire temperature range of this study (30-296 K) a minimum of four Gaussian curves are required. This approach is designed to give an approximation of the true band structure of the complex as a function of temperature. These Gaussian curves (G 1 -G 4 ) have maxima at 16,600, 18,260, 19,920, and 21,270 cm -1 ( Figure S1).

Public reporting burden for this collection of information is estimated to average 1 tiour per response, including ttie time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information it It does not display a currently valid 0MB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY) 10- PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)The Aerospace Corporation Laboratory Operations El Segundo, CA 90245-4691 SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) SPONSOR/MONITOR'S ACRONYM(S) SMC SPONSOR/MONITOR'S REPORT NUMBER(S)SMC-TR-04-20 ABSTRACTIn this work, polyaniline/poly(sulfonated styrene) nanofiber composites were prepared by an interfacial method. The insitu polymerization technique of these PANI nanofibers in the presence of sulfonated polystyrene allowed for the growth of PANI 2-D nanostructures embedded in the polymerized sulfonated host. This facile approach enables a self-assembly of these nanofibers into a workable, robust, conductive composite that can be processed and cast from water. A low accelerating voltage SEM was used to image these twisted fibers within the bulk of the cast film. In addition, the SEM confmned the self-assembly of these 40-50 nm fibers within the host PSS to yield an electrically conducting composite fihn. SUBJECT TERMSNanofibers, Conductive polymers, Interfacial polymerization, Self-assembled

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