The synthesis, spectral characterization, and electrochemical behavior of bis(tri-n-hexylsiloxy)(2,3-phthalocyaninato)silicon [SiPc(OR)2], its dimer [RO(SiPcO)2R], and its naphthalocyanine analogue [SiNc(OR)2] are described. All compounds show near-UV absorption corresponding to Soret and N bands and intense absorption in the visible-near-IR region corresponding to Q bands. In CH2C12, within the solvent stability limit, there are two reductions and one oxidation for SiPc(OR)2 and two reductions and two oxidations for RO(SiPcO)2R and SiNc(OR)2; all appear as reversible one-electron waves, although = 2 for the dimer. The difference in the peak potentials of the first oxidation and first reduction waves agrees well with the excitation energy and fluorescence (corresponding to Q bands) of SiPc(OR)2 and SiNc(OR)2. Both compounds emit upon electrochemical generation of reduced and oxidized forms (electrogenerated chemiluminescence, eel). The corrected eel maxima are near 684 nm for SiPc(OR)2 and 792 nm for SiNc(OR)2; the latter corresponds to the longest wavelength eel emission reported so far. The phthalocyanine dimer, RO(SiPcO)2R, is easier to reduce and easier to oxidize than the monomer.The voltammetric waves in this case involve two-electron transfers with peak splittings characteristic of le waves, suggesting that the two phthalocyanine rings in the dimer do not strongly interact. No fluorescence or eel was observed from the dimer.Phthalocyanine compounds often show high thermal and chemical stability and interesting optical and electrical properties.1"5 67We and others have been interested in the conductivities

The photoelectrochemical (PEC) behavior of n-and p-type WSe2 single crystal electrodes in aqueous solutions containing a number of redox couples (Br2/Br", Fe3+/Fe2+, I2/I", FefCNl^'/FefCN)^, and MV2+/MV+, where MV is methylviologen) was investigated. The results are consistent with a model of the interface where ideal behavior is approached with some couples but recombination effects are important with others. The characteristics of several PEC cells are described. The n-WSe2/I3" (0.025 ), (1.0 M)/Pt cell showed a 0.71-V open circuit voltage, 65 mA/cm2 short circuit current, 0.46 fill factor, and ~14% power efficiency under 150 mW/cm2 red light irradiation. A rechargeable PEC cell based on the p-WSe2/MV2+,I"/n-WSe2 system was constructed. Photoproduction of H2 and I2 with such a cell is also described.

Capacitance-voltage (C-V) measurements were made for the single crystal semiconductors n-TiO2, n-CdS, n-InP, p-Si, p-GaAs, n-and p-WSe2, and n-MoSe2 in acetonitrile containing a number of redox couples whose potentials (Vredox) spanned a potential regime much wider than the bandgaps. The flatband potential (VrB) evaluated from capacitance-potential (C-V) measurements (Mott-Schottky plots) exhibited three types of behavior with varying solution redox potentials: (i) VFB varied monotonically with Vredo • for p-Si, p-GaAs, and n:InP; (ii) for n-TiO2 and n-CdS, VFB did not shift for couples located negative of the midgap potential, but varied monotonically for couples positive of this value; (iii) for the layer-type, compounds (MoSe2, WSe~),VF, was almost independent of Vredo• These differences were ascribed to differences in surface-state densities. For n-TiO2 crystals, (001) face etched with molten KHSO4 and reduced, evidence for surface states at two different potentials was obtained from the in-phase component of the total admittance. Tentative assignment of these states is to lattice defects. The states closer to the conduction band are assigned to oxygen vacancies and the deeper states to Ti (III). The densities of surface states (N~) evaluated from GJ(o vs. (0 plots for TiO2 and p-Si are around 101~ and 101~ cm-2, respectively. These two values represent different situations, i.e., while the former value of N~s is not sufficient for pinning the Fermi level, the latter value is sufficiently high for the occurrence of Fermi level pinning.

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