Gold surfaces modified with C 3 -C 18 -alkanethiols (CH 3 (CH 2 ) X-1 SH; H X SH; x ) 3, 8, 12, 16, 18) and C 16alkanethiols, fluorinated at the outer 1, 2, 4, and 10 methylene positions (CF 3 (CF 2 ) Y-1 (CH 2 ) X SH; F y H x SH; y ) 1, x ) 15; y ) 2, x ) 14; y ) 4, x ) 12; y ) 10, x ) 6) were characterized by He(I) UV-photoelectron spectroscopy (UPS). (Detailed X-ray photoelectron spectroscopic characterization of the partially fluorinated thin films is given in the Supporting Information). Long incubation times of the gold surface with the alkanethiol solutions lead to compact monolayer films for all of the alkanethiols, as indicated by the exponential decrease in emission intensity versus alkyl chain length for both the gold Fermi edge (UPS data), and by a parallel decrease in Au(4f) photoemission intensity using X-ray photoelectron spectroscopy. Changes in the effective work function of these surfaces due to the presence of significant interfacial dipoles are observed (i) as alkyl chain length is increased, and (ii) as the fraction of fluorinated methylene groups is increased in a constant length alkyl chain. Negative shifts of the low kinetic energy photoemission edge with increasing alkyl chain length in the H x SH series are consistent with the presence of a large positive interface dipole. The largest part of this shift (ca. 1.0 eV) appears between the C 3 -and C 8 -alkyl chain lengths. Adding -CF x groups to the outer end of the C 16 -alkyl chain positively shifts the low-kinetic-energy photoemission edge, consistent with the presence of a large negative interface dipole that completely compensates for the positive dipole from the alkyl portion of the chain. Examining C 13 -C 16 alkyl chains fluorinated at only the outer methyl group shows that this negative dipole depends on the orientation of the -CF 3 group (i.e., "odd-even" effects in the effective work function are observed). Comparison of the shifts in gold/SAM vacuum level (changes in effective work function) as a function of the apparent dipole moment of the molecule provides an estimate of the band-edge offsets for these molecules on the gold surface, an estimate of the intrinsic shift in a vacuum level at zero dipole moment of the adsorbate, and an estimate of the intrinsic dipole moment for the gold-thiolate bond.

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Protection−deprotection of silyl-derivatized surface hydroxyl groups represents a new, “one-pot” strategy for the layer-by-layer construction of polar, covalently interlinked electrooptic molecular superlattices. These, siloxane-based multilayer structures are shown to be smooth, adherent, and structurally regular and to exhibit excellent electrooptic/nonlinear optic responses with χ(2) zzz ∼ 220 pm/V and r 33 ∼ 80 pm/V without electric field poling. This all “wet-chemical” self-assembly approach should be readily amenable to automation.

We demonstrate the use of chemical vapor deposition (CVD) to create unique thin (12-36 nm) and conformal TiO 2 interlayers on indium-tin oxide (ITO) electrodes, for use as electron collection contacts in inverted bulk heterojunction P 3 HT/PC 61 BM organic photovoltaics (OPVs). Optimized CVD formation of these oxide films is inherently scalable to large areas, and may be a viable non-contact alternative to electron-selective interlayer formation. Oxide-based electron-selective interlayers, such as TiO 2 , need to be thin, conformal and sufficiently electronically conducting films without sacrificing electron harvesting selectivity. Using volatile titanium-tetraisopropoxide (TTIP) precursors in a flowing N 2 gas stream, the CVD process provides nanometer control of film thickness to produce 12-36 nm thickness device-quality films. The best performing CVD films, processed at substrate temperatures of ca. 210 C, characterized using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were found to be amorphous but stoichiometric TiO 2 . Solution electrochemistries (voltammetry) of probe molecules were shown to be easily accessible indicators of film porosity and are predictive for electron harvesting selectivity (and hole-blocking) in an inverted configuration OPV platform. Small molecules whose redox potentials placed them energetically above the conduction band edge energy (E CB ) were reduced/ oxidized at nearly the same rates as for bare ITO. Probe molecules whose redox potentials place them energetically within the band gap region, below E CB , show almost complete blocking of their oxidation/reduction processes, for optimized conformal (and nonporous) TiO 2 films. In addition, background oxidation current densities for solution probe molecules correlate inversely with the shunt resistance (R P ) measured in OPVs. OPVs with the configuration: ITO/CVD-TiO 2 /P 3 HT:PC 61 BM/MoO 3 /Ag, using TiO 2 films of 12, 24 and 36 nm, were evaluated for short-circuit photocurrent (J SC ), open-circuit photopotential (V OC ), and fill-factor (FF), versus bare ITO. OPVs using amorphous, conformal 24 nm TiO 2 interlayers showed the highest fill factors, lowest R S , highest R P and power conversion efficiencies of ca. 3.7%.

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Exciplexes can be used as emission sources in light‐emitting devices (LEDs), as is demonstrated here. High electroluminescence is reported from bilayer organic LEDs in which the emission is confirmed to originate from an exciplex formed at the interface of two organic layers, for example of an aromatic diamine and a quinoxaline derivative, one of which is shown in the Figure.

Dye-sensitization processes for the (001) surface of n-type titanium oxide (n-TiO2) single crystal coated with vacuum-deposited titanylphthalocyanine (TiOPc) were investigated by means of photoelectrochemical measurements and X-ray and ultraviolet photoelectron spectroscopy (XPS, UPS). The electrode of n-TiO2 coated with TiOPc exhibited two photooxidation current bands in an aqueous electrolyte including hydroquinone (H2Q), due to direct excitation of n-TiO2 below 420 nm and electron transfer from TiOPc to n-TiO2 under the Q-band absorption of TiOPc at 600−800 nm, respectively. The former photocurrent process due to n-TiO2 excitation was remarkably decreased by presence of surface states, which originated from defects of oxygen induced by Ar ion bombardment of the n-TiO2 surface. The photooxidation process sensitized by the latter was evaluated from the determined energy levels of electronic bands for n-TiO2 and TiOPc. The LUMO level of TiOPc was located 0.3 eV above that of n-TiO2, which enabled electrons to transfer from TiOPc to n-TiO2. The excited state of TiOPc was not quenched by the surface states of n-TiO2 but was efficiently transferred to n-TiO2 at the n-TiO2/TiOPc interface.

High electron mobility in organic thin films has in general been difficult to achieve. Oxadiazole derivatives are among the most successful electron conducting/hole blocking materials employed in organic light‐emitting devices (OLEDs), the aluminum–oxadiazole complex presented here, tris(2‐(5‐phenyl‐1,3,4‐oxadiazol‐yl)phenonate) aluminum (AlPOP), being no exception. OLEDs based on AlPOP are reported to exhibit a strong blue emission with high external efficiency and brightness and excellent shelf lifetime stability.