A “Green” Route to Perylene Dyes: Direct Coupling Reactions of 1,8-Naphthalimide and Related Compounds under Mild Conditions Using a “New” Base Complex Reagent, <i>t</i>-BuOK/DBN

The direct coupling reactions of 1,8-naphthalimide compounds efficiently occurred at 130 or 170 °C without the intervention of the leuco form dyes in the presence of base complex reagent, t-BuOK/1,5-diazabicyclo[4.3.0]non-5-ene (DBN), to give the corresponding perylene dyes in good yields with >95% purities. A possible mechanistic speculation for these oxidative coupling reactions is briefly discussed

A “Green” Route to Perylene Dyes: Direct Coupling Reactions of 1,8-Naphthalimide and Related Compounds under Mild Conditions Using a “New” Base Complex Reagent, <i>t</i>-BuOK/DBN

The direct coupling reactions of 1,8-naphthalimide compounds efficiently occurred at 130 or 170 °C without the intervention of the leuco form dyes in the presence of base complex reagent, t-BuOK/1,5-diazabicyclo[4.3.0]non-5-ene (DBN), to give the corresponding perylene dyes in good yields with >95% purities. A possible mechanistic speculation for these oxidative coupling reactions is briefly discussed

Control of Molecular Aggregation Features in Polymer-Dispersed Liquid Crystal Films Utilizing a Boronate-Terminated Self-Assembled Monolayer

Control of Molecular Aggregation Features in Polymer-Dispersed Liquid Crystal Films Utilizing a Boronate-Terminated Self-Assembled Monolaye

Catalytic Activities of CuSO₄/Al₂O₃ in Dehydrogenation of Arenes by Dioxygen

The oxidation reactions of hydroquinones, 2-naphthols, or 2,6-di-tert-butylphenol efficiently occurred by catalysis with alumina-supported copper(II) sulfate to give the corresponding benzoquinones, 1,1‘-bi-2-naphthols, and 4,4‘-diphenoquinone, respectively, in good yields. The synthetic potentiality of the catalytic reactions was demonstrated by easy isolation of the final products using only filtration and solvent evaporation as well as by application to large-scale syntheses of the benzoquinones and binaphthols. The catalysis with alumina-supported copper(II) sulfate was also applied to the oxidative intramolecular coupling of 5,5‘-diacenaphthene to the corresponding perylene compound

Anchoring Effects of Self-Assembled Monolayers for Polymer-Dispersed Liquid Crystal Films

Polymer-dispersed liquid crystal (PDLC) films of 4-cyano-4‘-pentylbiphenyl (5CB) were fabricated between two quartz substrates, the surfaces of which had been modified with the self-assembled monolayers (SAMs) of CH3−(CH2)17−Si(OMe)3 (1), HS−(CH2)10−Si(OEt)3 (2), and NC−(CH2)11−Si(OEt)3 (3). The SAM-modification effects on the molecular aggregation of 5CB were investigated by steady-state and time-resolved fluorescence analysis for the PDLC films. Remarkably, it was found that selective excitation of the interface layer with the substrate surface gave both the monomer and excimer emissions of 5CB in relative intensities, depending on the chemical nature of the SAM surfaces. While the monomer and excimer emissions appeared in comparative intensities in the case of the unmodified quartz surface, the surface modification with the SAM of 1 resulted in a dominant contribution of the excimer emission. By contrast, the monomer emission was much stronger than the excimer emission in the case of the surface modified by the SAM of 2. The surface modification with the SAM of 3 gave a fluorescence spectrum very similar to that in the case of the unmodified surface. Fluorescence decay analysis for the PDLC films revealed that the excimer emission consists of two components with shorter (1.3−1.6 ns) and longer (10−12 ns) lifetimes, whose relative contributions depend on the SAM modifications. The molecular pictures of 5CB depicted from the decay dynamics are in good agreement with those derived from the steady-state fluorescence behavior of the PDLC films. Electrooptic devices based on the PDLC films were constructed by using indium−tin oxide transparent electrodes modified with the SAMs, and it was confirmed that the electrooptic responses again significantly depend on the modifications of the substrate surface. The dependency of the fluorescence and electrooptic behavior on the surface modifications for the PDLC films has been discussed in terms of anchoring effects of the substrate surfaces, which effectively work even in heterogeneous materials such as PDLCs

Inorganometallic Photocatalyst for CO₂ Reduction

ConspectusDuring the last few decades, the design of catalytic systems for CO2 reduction has been extensively researched and generally involves (1) traditional approaches using molecular organic/organometallic materials and heterogeneous inorganic semiconductors and (2) combinatory approaches wherein these materials are combined as needed. Recently, we have devised a number of new TiO2-mediated multicomponent hybrid systems that synergistically integrate the intrinsic merits of various materials, namely, molecular photosensitizers/catalysts and n-type TiO2 semiconductors, and lower the energetic and kinetic barriers between components. We have termed such multicomponent hybrid systems assembled from the hybridization of various organic/inorganic/organometallic units in a single platform inorganometallic photocatalysts. The multicomponent inorganometallic (MIOM) hybrid system onto which the photosensitizer and catalyst are coadsorbed efficiently eliminates the need for bulk-phase diffusion of the components and avoids the accumulation of radical intermediates that invokes a degradation pathway, in contrast to the homogeneous system, in which the free reactive species are concentrated in a confined reaction space. In particular, in energetic terms, we discovered that in nonaqueous media, the conduction band (CB) levels of reduced TiO2 (TiO2(e–)) are positioned at a higher level (in the range −1.5 to −1.9 V vs SCE). This energetic benefit of reduced TiO2 allows smooth electron transfer (ET) from injected electrons (TiO2(e–)) to the coadsorbed CO2 reduction catalyst, which requires relatively high reducing power (at least more than −1.1 V vs SCE). On the other hand, the existence of various shallow surface trapping sites and surface bands, which are 0.3–1.0 eV below the CB of TiO2, efficiently facilitates electron injection from any photosensitizer (including dyes having low excited energy levels) to TiO2 without energetic limitation. This is contrasted with most photocatalytic systems, wherein successive absorption of single high-energy photons is required to produce excited states with enough energy to fulfill photocatalytic reaction, which may allow unwanted side reactions during photocatalysis. In this Account, we present our recent research efforts toward advancing these MIOM hybrid systems for photochemical CO2 reduction and discuss their working mechanisms in detail. Basic ET processes within the MIOM system, including intervalence ET in organic/organometallic redox systems, metal-to-ligand charge transfer of organometallic complexes, and interfacial/outer-sphere charge transfer between components, were investigated by conducting serial photophysical and electrochemical analyses. Because such ET events occur primarily at the interface between the components, the efficiency of interfacial ET between the molecular components (organic/organometallic photosensitizers and molecular reduction catalysts) and the bulk inorganic solid (mainly n-type TiO2 semiconductors) has a significant influence on the overall photochemical reaction kinetics and mechanism. In some TiO2-mediated MIOM hybrids, the chemical attachment of organic or organometallic photosensitizing units onto TiO2 semiconductors efficiently eliminates the step of diffusion/collision-controlled ET between components and prevents the accumulation of reactive species (oxidatively quenched cations or reductively quenched anions) in the reaction solution, ensuring steady photosensitization over an extended reaction period. The site isolation of a single-site organometallic catalyst employing TiO2 immobilization promotes the monomeric catalytic pathway during the CO2 reduction process, resulting in enhanced product selectivity and catalytic performance, including lifetime extension. In addition, as an alternative inorganic solid scaffold, the introduction of a host porphyrin matrix (interlinked in a metal–organic framework (MOF) material) led to efficient and durable photocatalytic CO2 conversion by the new MOF–Re­(I) hybrid as a result of efficient light harvesting/exciton migration in the porphyrinic MOF and rapid quenching of the photogenerated electrons by the doped Re­(I) catalytic sites. Overall, the case studies presented herein provide valuable insights for the rational design of advanced multicomponent hybrid systems for artificial photosynthesis involving CO2 reduction

Electronic Optimization of Heteroleptic Ru(II) Bipyridine Complexes by Remote Substituents: Synthesis, Characterization, and Application to Dye-Sensitized Solar Cells

We prepared a series of new heteroleptic ruthenium(II) complexes, Ru(NCS)2LL′ (3a−3e), where L is 4,4′-di(hydroxycarbonyl)-2,2′-bipyridine and L′ is 4,4′-di(p-X-phenyl)-2,2′-pyridine (X = CN (a), F (b), H (c), OMe (d), and NMe2 (e)), in an attempt to explore the structure−activity relationships in their photophysical and electrochemical behavior and in their performance in dye-sensitized solar cells (DSSCs). When substituent X is changed from electron-donating NMe2 to electron-withdrawing CN, the absorption and emission maxima reveal systematic bathochromic shifts. The redox potentials of these dyes are also significantly influenced by X. The electronic properties of the dyes were theoretically analyzed using density functional theory calculations; the results show good correlations with the experimental results. The solar-cell performance of DSSCs based on dye-grafted nanocrystalline TiO2 using 3a−3e and standard N3 (bis[(4,4′-carboxy-2,2′-bipyridine)(thiocyanato)]ruthenium(II)) were compared, revealing substantial dependences on the dye structures, particularly on the remote substituent X. The 3d-based device showed the best performance: η = 8.30%, JSC = 16.0 mA·cm−2, VOC = 717 mV, and ff = 0.72. These values are better than N3-based device

Highly Robust Hybrid Photocatalyst for Carbon Dioxide Reduction: Tuning and Optimization of Catalytic Activities of Dye/TiO₂/Re(I) Organic–Inorganic Ternary Systems

Herein we report a detailed investigation of a highly robust hybrid system (sensitizer/TiO₂/catalyst) for the visible-light reduction of CO₂ to CO; the system comprises 5′-(4-[bis­(4-methoxy­methyl­phenyl)­amino]­phenyl-2,2′-dithiophen-5-yl)­cyano­acrylic acid as the sensitizer and (4,4′-bis­(methyl­phosphonic acid)-2,2′-bipyridine)­Re^I(CO)₃Cl as the catalyst, both of which have been anchored on three different types of TiO₂ particles (s-TiO₂, h-TiO₂, d-TiO₂). It was found that remarkable enhancements in the CO₂ conversion activity of the hybrid photocatalytic system can be achieved by addition of water or such other additives as Li⁺, Na⁺, and TEOA. The photocatalytic CO₂ reduction efficiency was enhanced by approximately 300% upon addition of 3% (v/v) H₂O, giving a turnover number of ≥570 for 30 h. A series of Mott–Schottky (MS) analyses on nanoparticle TiO₂ films demonstrated that the flat-band potential (<i>V</i>_fb) of TiO₂ in dry DMF is substantially negative but positively shifts to considerable degrees in the presence of water or Li⁺, indicating that the enhancement effects of the additives on the catalytic activity should mainly arise from optimal alignment of the TiO₂ <i>V</i>_fb with respect to the excited-state oxidation potential of the sensitizer and the reduction potential of the catalyst in our ternary system. The present results confirm that the TiO₂ semiconductor in our heterogeneous hybrid system is an essential component that can effectively work as an electron reservoir and as an electron transporting mediator to play essential roles in the persistent photocatalysis activity of the hybrid system in the selective reduction of CO₂ to CO

Significance of Hydrophilic Characters of Organic Dyes in Visible-Light Hydrogen Generation Based on TiO₂

A series of dyes were synthesized to examine the roles of the hydrophilic characteristics of R in sensitized hydrogen generation by dye-grafted Pt/TiO2 under visible light irradiation. The hydrogen-generation efficiencies and optimum amounts of the dyes grafted to Pt/TiO2 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

Highly Selective and Durable Photochemical CO₂ Reduction by Molecular Mn(I) Catalyst Fixed on a Particular Dye-Sensitized TiO₂ Platform

A Mn­(I)-based hybrid system (OrgD-|TiO2|-MnP) for photocatalytic CO2 reduction is designed to be a coassembly of Mn­(4,4′-Y2-bpy)­(CO)3Br (MnP; Y = CH2PO­(OH)2) and (E)-3-[5-(4-(diphenylamino)­phenyl)-2,2′-bithiophen-2′-yl]-2-cyanoacrylic acid (OrgD) on TiO2 semiconductor particles. The OrgD-|TiO2|-MnP hybrid reveals persistent photocatalytic behavior, giving high turnover numbers and good product selectivity (HCOO– versus CO). As a typical run, visible-light irradiation of the hybrid catalyst in the presence of 0.1 M electron donor (ED) and 0.001 M LiClO4 persistently produced HCOO– with a >99% selectivity accompanied by a trace amount of CO; the turnover number (TONformate) reached ∼250 after 23 h of irradiation. The product selectivity (HCOO–/CO) was found to be controlled by changing the loading amount of MnP on the TiO2 surface. In situ FTIR analysis of the hybrid during photocatalysis revealed that, at low Mn concentration, the Mn–H monomeric mechanism associated with HCOO– formation is dominant, whereas at high Mn concentration, CO is formed via a Mn–Mn dimer mechanism