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Finding a selective and efficient fragmentation process under ambient conditions is pivotal for the generation of fuels and chemical feedstocks from lignoceullosic biomass. In the present study, visible-light and amine-functionalized fullerene-based photocatalyst-promoted photodegradation reactions of dimeric β-O-4 and β-1 lignin model compounds, containing varying numbers of methoxy substituents on the arene ring, were explored to find and develop mild, eco-friendly photochemical techniques for efficient delignification. The results showed that, in contrast to well-known organic photoredox catalysts, amine-functionalized fullerene photocatalyst promoted photochemical reactions of lignin model compounds could lead to more efficient lignin fragmentation reactions through a pathway involving a selective C

Knowledge about factors that govern chemoselectivity is pivotal to the design of reactions that are utilized to produce complex organic substances. In the current study, SET-promoted photoaddition ...

Excited-state intramolecular proton transfer (ESIPT) is a fundamental ultrafast photochemical process. Although it has been intensively studied for the development of novel photonic devices such as...

A series of perylene-based donor–acceptor–donor (D–A–D) compounds, 3,9-bis(p-(R)-diphenylamino)perylene (R: CN (2a), F (2b), H (2c), Me (2d), and OMe (2e)), was synthesized using 3,9-dibromoperylen...

Visible-light-driven water splitting was investigated in a dye sensitized photoelectrosynthesis cell (DSPEC) based on a photoanode with a phosphonic acid-derivatized donor−π–acceptor (D−π–A) organic chromophore, 1, and the water oxidation catalyst [Ru(bda)(4-O(CH2)3P(O3H2)2-pyr)2], 2, (pyr = pyridine; bda = 2,2′-bipyridine-6,6′-dicarboxylate). The photoanode was prepared by using a layering strategy beginning with the organic dye anchored to an FTO|core/shell electrode, atomic layer deposition (ALD) of a thin layer (

We report on the synthesis and photophysical properties of a photocathode consisting of a molecular bilayer structure self-assembled on p-type NiO nanostructured films. The resulting photocathode and its nanostructured indium–tin oxide analog absorb visible light and convert it into injected holes with injection yields of ∼30%, measured at the first observation time by nanosecond transient absorption spectroscopy, and long-lived reducing equivalents that last for several milliseconds without applied bias. An initial quantum yield of 15% was achieved for photogeneration of the reduced dye on the p-NiO electrode. Nanosecond transient absorption experiments and detailed analyses of the underlying electron transfer steps demonstrate that the overall efficiency of the cell is limited by hole injection and charge recombination processes. Compared with the highly doped indium–tin oxide photocathode, the NiO photocathode shows superior photoconversion efficiencies for generating reducing equivalents and longer li...

Tandem junction photoelectrochemical water-splitting devices, whereby two light absorbing electrodes targeting separate portions of the solar spectrum generate the voltage required to convert water to oxygen and hydrogen, enable much higher possible efficiencies than single absorber systems. We report here on the development of a tandem system consisting of a dye-sensitized photoelectrochemical cell (DSPEC) wired in series with a dye-sensitized solar cell (DSC). The DSPEC photoanode incorporates a tris(bipyridine)ruthenium(II)-type chromophore and molecular ruthenium based water oxidation catalyst. The DSPEC was tested with two more-red absorbing DSC variations, one utilizing N719 dye with an I3–/I– redox mediator solution and the other D35 dye with a tris(bipyridine)cobalt ([Co(bpy)3]3+/2+) based mediator. The tandem configuration consisting of the DSPEC and D35/[Co(bpy)3]3+/2+ based DSC gave the best overall performance and demonstrated the production of H2 from H2O with the only energy input from simul...

Layer-by-Layer (LbL) polyelectrolyte self-assembly occurs by the alternate exposure of a substrate to solutions of oppositely charged polyelectrolytes or polyions. Here, we report the application of LbL to construct chromophore–catalyst assemblies consisting of a cationic polystyrene-based Ru polychromophore (PS-Ru) and a [Ru(tpy)(2-pyridyl-N-methylbenzimidazole) (OH2)]2+ water oxidation catalyst (RuC), codeposited with poly(acrylic acid) (PAA) as an inert polyanion. These assemblies are deposited onto planar indium tin oxide (ITO, Sn:In2O3) substrates for electrochemical characterization and onto mesoporous substrates consisting of a SnO2/TiO2 core/shell structure atop fluorine doped tin oxide (FTO) for application to light-driven water oxidation in a dye-sensitized photoelectrosynthesis cell. Cyclic voltammetry and ultraviolet–visible absorption spectroscopy reveal that multilayer deposition progressively increases the film thickness on ITO glass substrates. Under an applied bias, photocurrent measureme...

An electrochemical procedure for preparing chromophore-catalyst assemblies on oxide electrode surfaces by reductive vinyl coupling is described. On core/shell SnO2/TiO2 nanoparticle oxide films, excitation of the assembly with 1 sun (100 mW cm–2) illumination in 0.1 M H2PO4–/HPO42– at pH 7 with an applied bias of 0.4 V versus SCE leads to water splitting in a DSPEC with a Pt cathode. Over a 5 min photolysis period, the core/shell photoanode produced O2 with a faradaic efficiency of 22%. Instability of the surface bound chromophore in its oxidized state in the phosphate buffer leads to a gradual decrease in photocurrent and to the relatively modest faradaic efficiencies.

The mechanism of electrocatalytic water oxidation by the water oxidation catalyst, ruthenium 2,2′-bipyridine-6,6′-dicarboxylate (bda) bis-isoquinoline (isoq), [Ru(bda)(isoq)2], 1, at metal oxide electrodes has been investigated. At indium-doped tin oxide (ITO), diminished catalytic currents and increased overpotentials are observed compared to glassy carbon (GC). At pH 7.2 in 0.5 M NaClO4, catalytic activity is enhanced by the addition of [Ru(bpy)3]2+ (bpy = bipyridine) as a redox mediator. Enhanced catalytic rates are also observed at ITO electrodes derivatized with the surface-bound phosphonic acid derivative [Ru(4,4′-(PO3H2)2bpy)(bpy)2]2+, RuP2+. Controlled potential electrolysis with measurement of O2 at ITO with and without surface-bound RuP2+ confirm that water oxidation catalysis occurs. Remarkable rate enhancements are observed with added acetate and phosphate, consistent with an important mechanistic role for atom-proton transfer (APT) in the rate-limiting step as described previously at GC elect...

On the basis of the results of frontier orbital considerations, 4-substituted-2'-pyridyltriazoles were designed to serve as ancillary ligands in 2-phenylpyridine main ligand containing heteroleptic iridium(III) complexes that display deep blue phosphorescence emission. The iridium(III) complexes, Ir1-Ir7, prepared using the new ancillary ligands, were found to display structured, highly quantum efficient (Φp = 0.20-0.42) phosphorescence with emission maxima in the blue to deep blue 448-456 nm at room temperature. In accord with predictions based on frontier orbital considerations, the complexes were observed to have emission properties that are dependent on the electronic nature of substituents at the C-4 position of the pyridine moiety of the ancillary ligand. Importantly, placement of an electron-donating methyl group at C-4' of the pyridine ring of the 5-(pyridine-2'-yl)-3-trifluoromethyl-1,2,4-triazole ancillary ligand leads to an iridium(III) complex that displays a deep blue phosphorescence emission maximum at 448 nm in both the liquid and film states at room temperature. Finally, an OLED device, constructed using an Ir-complex containing the optimized ancillary ligand as the dopant, was found to emit deep blue color with a CIE of 0.15, 0.18, which is close to the perfect goal of 0.15, 0.15.

We prepared dendrimers of heteroleptic iridium(III) complexes, [(dfppy–Cz1)2Ir(dpq)]+ (G1) and [(dfppy–Cz2)2Ir(dpq)]+ (G2), which have the dfppy ligand connected to carbazole-functionalized dendron Czn (n = 1, 2) [dfppy–Czn = 5-Czn-2-(4,6-difluorophenyl)pyridine, dpq = 2,3-bis-(2-pyridyl)-qinoxaline, Cz1 = 4-(9-carbazolyl)benzyloxymethyl, and Cz2 = 4-[1,3-bis(9-carbazolyl)benzyloxy]benzyloxymethyl]. While parent complex [(dfppy)2Ir(dpq)]+ (G0) shows an intense emission at ∼635 nm with a lifetime of 1 μs assigned to dpq-based metal-to-ligand charge-transfer (MLCT) phosphorescence, excitation of the dendrimers at either carbazole (309 nm) or MLCT band (355 nm) resulted in markedly weaker and much shorter-lived MLCT emission (τp = 44 ns for G1 and 115 ns for G2) at room temperature. Upon exciting the carbazole chromophore of G1 and G2 at 309 nm, furthermore, both the carbazole fluorescence and the MLCT emission were very weak at room temperature. It was found that the lifetime of carbazole fluorescence is 20...

A series of dyes were synthesized to examine the roles of the hydrophilic characteristics of R in sensitized hydrogen generation by dye-grafted Pt/TiO(2) under visible light irradiation. The hydrogen-generation efficiencies and optimum amounts of the dyes grafted to Pt/TiO(2) were affected substantially by the hydrophilic and steric effects of R; moderately hydrophilic DEO1 and DEO2 showed higher sensitization activity at a lower loading than hydrophobic D-H.

Bis(4-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)phenyl)dimethylsilane (SiTAZ) was designed and synthesized as an electron-transporting material for deep blue phosphorescent organic light-emitting devices (PHOLEDs). Introducing a Si atom between two 3,4,5-triphenyl-1,2,4-triazole molecules, a high triplet energy of 2.84 eV, high glass transition temperature of 115 °C, and high electron mobility of 6.2 × 10−4 cm2 V−1 s−1 were achieved. By employing SiTAZ as a hole-blocking and electron-transporting material of iridium(III)[bis(4,6-difluorophenyl)pyridinato-N,C2′]tetrakis(1-pyrazolyl)borate (FIr6)-based deep blue phosphorescent OLEDs, a maximum external quantum efficiency (EQE) of 15.5%, an EQE of 13.8% at high luminance of 1000 cd m−2, and deep blue color coordinates of (0.16, 0.22) were achieved. The reduced efficiency roll-off at high luminance was attributed to the high triplet energy of the SiTAZ.

Wide-band-gap phosphorescent organic light-emitting diode (OLED) host materials were developed employing the tetrahedral structural motif of the silicon atom, which functioned further to connect the 4-(N-carbazolyl)phenyl (CP) units in its periphery (2a−2d). The thermal, photophysical, and electrochemical properties, and X-ray structural studies as well as OLED device characteristics were fully investigated. Silicon effectively disconnected the charge delocalization between the CP units. By low temperature PL study, the triplet energy was measured to be around 3.0 eV for all prepared host materials. The thermal stability correlated well with the number of CP units adorned at the silicon atom, showing a gradual increase in Tg values of 99−214 °C as the number of CP units increased in the 2a−d series. Further structural modification was carried out with the phenylsilane series (3a−c). Hole mobility measurements for the silicon-tuned host materials of the methyl and phenyl series, 2b−c and 3b−c showed mobili...

Panchromatic 1,6-bis(N-phenyl-p-(R)-phenylamino)pyrenes, 2R, were obtained from Buchwald-Hartwig coupling reactions between N-phenyl-p-(R)-phenylamines and 1,6-dibromopyrene. The photophysical properties of 2R corresponded well to the electron-withdrawing and -donating nature of the diarylamine substituents, exhibiting a full color visible range between 454 and 620 nm. In particular, a deep blue 2CN showed a high radiative rate constant of 2.85 x 10(8) s(-1) with high emission quantum efficiency of 79%. Further applications of 2CN as a blue dopant were attempted using multilayer organic light-emitting devices. A maximum efficiency of 3.98 cd/A with CIE coordinates of x = 0.14, y = 0.10 were obtained.