Visible Light–Driven Hydrogen Production by Carbon based Polymeric Materials

Converting solar energy into storable solar fuels such as H2 from earth abundant source—water—is a nice approach to find the solution of energy crisis and environmental protection. There are two half reactions; first, water oxidation into oxygen and proton and followed by proton reduction led to H2 evolution from water. After two decades of continuous attempts, there have been several efficient water oxidation photocatalysts introduced, whereas the proton reduction photocatalyst were relatively less explored. Major portion of reported photocatalysts for proton reduction are mainly derived from either noble metals or precious metals. Carbon-based organic photocatalysts have become attractive recently. These organic materials have several advantages like light weight, cheap, well-defined structure-property relationship and the most attractive one is better batch to batch reproducibility. Here, the reported organic photocatalysts and their performance are summarized which in fact help others to get an idea about ongoing progress in this area of research and to understand the basic designing principle for efficient photocatalysts for fuel production

Charge Delocalization in a Homologous Series of a,a’-Bis(dianisylamino)-Substituted Thiophene Monocations

A homologous series of three molecules containing thiophene, bithiophene, and terthiophene bridges between two redox-active tertiary amino groups was synthesized and explored. Charge delocalization in the one-electron-oxidized forms of these molecules was investigated by a combination of cyclic voltammetry, near-infrared optical absorption spectroscopy, and EPR spectroscopy. All three cation radicals can be described as organic mixed-valence species, and for all of them the experimental data are consistent with strong delocalization of the unpaired electron. Depending on what model is used for analysis of the optical absorption data, estimates for the electronic coupling matrix element (HAB) range from ∼5000 to ∼7000 cm–1 for the shortest member of the homologous series. According to optical absorption and EPR spectroscopy, even the terthiophene radical appears to belong either to Robin–Day class III or to a category of radicals commonly denominated as borderline class II/class III systems. The finding of such a large extent of charge delocalization over up to three adjacent thiophene units is remarkable

Benzoselenadiazole Containing Donor–Acceptor–Donor Small Molecules: Nonbonding Interactions, Packing Patterns, and Optoelectronic Properties

Herein, we describe the fine-tuning of intermolecular Se···N interaction in benzoselenadiazole (BDS) derivatives to form head-to-head dimers in the solid state. The structures and photophysical properties of phenyl-, thiophene-, and selenophene-capped BDS (<b>1–3</b>, respectively) are studied here. Because of the presence of the strong intramolecular Se···N interaction, selenophene-capped BDS <b>3</b> showed <i>syn</i> arrangement of two capped selenophene rings, whereas two thiophene rings in <b>2</b> showed an <i>anti</i> orientation. Compounds <b>1</b> and <b>2</b> showed the tendency to form head-to-head dimers in the solid state through the intermolecular Se···N interactions. In contrast to compounds <b>1</b> and <b>2</b>, compound <b>3</b> does not form a dimer in the solid state and, instead, shows strong intramolecular Se···N interactions. The tendency to form dimers largely depends on the nonbonding interactions and the steric effect of capped rings

Cyclopenta[<i>c</i>]thiophene-Based D–A Conjugated Copolymers: Effect of Heteroatoms (S, Se, and N) of Benzazole Acceptors on the Properties of Polymers

Three new donor–acceptor (D–A) type copolymers <b>P1</b>, <b>P2</b>, and <b>P3</b> have been synthesized by Stille condensation between the distannyl derivative of thiophene-capped cyclopenta­[<i>c</i>]­thiophene (CPT) with 4,7-dibromo­[2,1,3]­benzothiadiazole, 4,7-dibromo­[2,1,3]­benzoselenadiazole, and 4,7-dibromo­[2,1,3]­benzotriazole, respectively. These new CPT-based D–A copolymers showed an interesting trend of visible color (red, green, and blue) in solution as the acceptor was varied keeping the donor constant. The optical band gaps of the polymers, which were estimated by measuring the absorption onset in the UV–vis spectra of the film, were found to be 1.57, 1.44, and 1.86 eV for <b>P1</b>, <b>P2</b>, and <b>P3</b>, respectively. DFT calculations correlated the strength of the acceptors with the interesting trend in the colors of these (D)_nonvariant–(A)_variant copolymers. Compared with the solution, the film state absorption of <b>P2</b> and <b>P3</b> was significantly red-shifted compared to that of <b>P1</b>, indicating the presence of strong interchain interactions due to efficient self-π-stacking in the solid state

Solution Processable Benzooxadiazole and Benzothiadiazole Based D‑A‑D Molecules with Chalcogenophene: Field Effect Transistor Study and Structure Property Relationship

We present here the physicochemical characterization of a series of D-A-D type molecules which comprise benzooxadiazole (BDO) and benzothiadiazole (BDT) core symmetrically linked to two aromatic-heterols (furan (F), thiophene (T) and selenophene (Se)) at 4 and 7-positions. The molecular structures of four compounds <b>2</b> (T-BDO-T), <b>3</b> (Se-BDO-Se), <b>5</b> (T-BDT-T), and <b>6</b> (Se-BDT-Se) were determined by single-crystal X-ray diffraction. The combination of chalcogen atoms of benzochalcogenadiazole and chalcogenophene in D-A-D molecules has significant impact on their molecular packing in crystal structures. Structural analyses and theoretical calculations showed that all the molecules are nearly planar. Crystal structures of <b>2</b>, <b>3</b>, <b>5</b>, and <b>6</b> showed significant short range interactions such as π···π, CH···π, S···π, Se···π, N···H, O···H, S···H, Se···H, S···O, and Se···N interactions, which influence crystal packing and orientation of the capped aromatic-heterol rings with respect to the central BDO or BDT unit. The π-stacking interactions have been observed via intermolecular overlap of the donor with acceptor units of the adjacent molecules which facilitate the charge transport process. Good thermal stability and solubility in common organic solvents make them good candidate for flexible electronics. Interestingly, the molecules <b>2</b>, <b>3</b>, and <b>6</b> have the propensity to form ordered crystallites when sheared during the drying process in the thin films. Devices based on these solution processable all organic FETs demonstrated hole mobility as high as 0.08 cm² V^–1 s^–1 and <i>I</i>_on/<i>I</i>_off ratio of 10⁴

Solution Processable Benzooxadiazole and Benzothiadiazole Based D‑A‑D Molecules with Chalcogenophene: Field Effect Transistor Study and Structure Property Relationship

We present here the physicochemical characterization of a series of D-A-D type molecules which comprise benzooxadiazole (BDO) and benzothiadiazole (BDT) core symmetrically linked to two aromatic-heterols (furan (F), thiophene (T) and selenophene (Se)) at 4 and 7-positions. The molecular structures of four compounds <b>2</b> (T-BDO-T), <b>3</b> (Se-BDO-Se), <b>5</b> (T-BDT-T), and <b>6</b> (Se-BDT-Se) were determined by single-crystal X-ray diffraction. The combination of chalcogen atoms of benzochalcogenadiazole and chalcogenophene in D-A-D molecules has significant impact on their molecular packing in crystal structures. Structural analyses and theoretical calculations showed that all the molecules are nearly planar. Crystal structures of <b>2</b>, <b>3</b>, <b>5</b>, and <b>6</b> showed significant short range interactions such as π···π, CH···π, S···π, Se···π, N···H, O···H, S···H, Se···H, S···O, and Se···N interactions, which influence crystal packing and orientation of the capped aromatic-heterol rings with respect to the central BDO or BDT unit. The π-stacking interactions have been observed via intermolecular overlap of the donor with acceptor units of the adjacent molecules which facilitate the charge transport process. Good thermal stability and solubility in common organic solvents make them good candidate for flexible electronics. Interestingly, the molecules <b>2</b>, <b>3</b>, and <b>6</b> have the propensity to form ordered crystallites when sheared during the drying process in the thin films. Devices based on these solution processable all organic FETs demonstrated hole mobility as high as 0.08 cm² V^–1 s^–1 and <i>I</i>_on/<i>I</i>_off ratio of 10⁴

A heavy metal-free CuInS2 quantum dot sensitized NiO photocathode with a Re molecular catalyst for photoelectrochemical CO2 reduction

Heavy metal-free CuInS2 quantum dots (QDs) were employed as a photosensitizer on a NiO photocathode to drive an immobilized molecular Re catalyst for photoelectrochemical CO2 reduction for the first time. A photocurrent of 25 mu A cm(-2) at -0.87 V vs. NHE was obtained, providing a faradaic efficiency of 32% for CO production

Insights into the Mechanism of a Covalently Linked Organic Dye-Cobaloxime Catalyst System for Dye-Sensitized Solar Fuel Devices

A covalently-linked organic dye-cobaloxime catalyst system is developed by facile click reaction for mechanistic studies and application in a dye sensitized solar fuel device based on mesoporous NiO. This system has been systematically investigated by photophysical measurements, density functional theory, time resolved fluorescence, transient absorption spectroscopy as well as photoelectron spectroscopy. The results show that irradiation of the dye-catalyst on NiO leads to ultrafast hole injection into NiO from the excited dye, followed by a fast electron transfer to reduce the catalyst unit. Moreover, they suggest that the dye undergoes structural changes in the excited state and that excitation energy transfer occurs between neighboring molecules. The photoelectrochemical experiments also show the hydrogen production by this system-based NiO photocathode. The axial chloride ligands of the catalyst are released during photocatalysis to create the active sites for proton reduction. A working mechanism of the dye-catalyst on photocathode is eventually proposed on the basis of this study

Covalently linking CuInS2 quantum dots with a Re catalyst by click reaction for photocatalytic CO2 reduction

Covalently linking photosensitizers and catalysts in an inorganic-organic hybrid photocatalytic system is beneficial for efficient electron transfer between these components. However, general and straightforward methods to covalently attach molecular catalysts on the surface of inorganic semiconductors are rare. In this work, a classic rhenium bipyridine complex (Re catalyst) has been successfully covalently linked to the low toxicity CuInS2 quantum dots (QDs) by click reaction for photocatalytic CO2 reduction. Covalent bonding between the CuInS2 QDs and the Re catalyst in the QD-Re hybrid system is confirmed by UV-visible absorption spectroscopy, Fourier-transform infrared spectroscopy and energy-dispersive X-ray measurements. Time-correlated single photon counting and ultrafast time-resolved infrared spectroscopy provide evidence for rapid photo-induced electron transfer from the QDs to the Re catalyst. Upon photo-excitation of the QDs, the singly reduced Re catalyst is formed within 300 fs. Notably, the amount of reduced Re in the linked hybrid system is more than that in a sample where the QDs and the Re catalyst are simply mixed, suggesting that the covalent linkage between the CuInS2 QDs and the Re catalyst indeed facilitates electron transfer from the QDs to the Re catalyst. Such an ultrafast electron transfer in the covalently linked CuInS2 QD-Re hybrid system leads to enhanced photocatalytic activity for CO2 reduction, as compared to the conventional mixture of the QDs and the Re catalyst