Fifty Shades of Phenanthroline: Synthesis Strategies to Functionalize 1,10-Phenanthroline in All Positions.

1,10-Phenanthroline (phen) is one of the most popular ligands ever used in coordination chemistry due to its strong affinity for a wide range of metals with various oxidation states. Its polyaromatic structure provides robustness and rigidity, leading to intriguing features in numerous fields (luminescent coordination scaffolds, catalysis, supramolecular chemistry, sensors, theranostics, etc.). Importantly, phen offers eight distinct positions for functional groups to be attached, showcasing remarkable versatility for such a simple ligand. As a result, phen has become a landmark molecule for coordination chemists, serving as a must-use ligand and a versatile platform for designing polyfunctional arrays. The extensive use of substituted phenanthroline ligands with different metal ions has resulted in a diverse array of complexes tailored for numerous applications. For instance, these complexes have been utilized as sensitizers in dye-sensitized solar cells, as luminescent probes modified with antibodies for biomaterials, and in the creation of elegant supramolecular architectures like rotaxanes and catenanes, exemplified by Sauvage's Nobel Prize-winning work in 2016. In summary, phen has found applications in almost every facet of chemistry. An intriguing aspect of phen is the specific reactivity of each pair of carbon atoms ([2,9], [3,8], [4,7], and [5,6]), enabling the functionalization of each pair with different groups and leading to polyfunctional arrays. Furthermore, it is possible to differentiate each position in these pairs, resulting in non-symmetrical systems with tremendous versatility. In this Review, the authors aim to compile and categorize existing synthetic strategies for the stepwise polyfunctionalization of phen in various positions. This comprehensive toolbox will aid coordination chemists in designing virtually any polyfunctional ligand. The survey will encompass seminal work from the 1950s to the present day. The scope of the Review will be limited to 1,10-phenanthroline, excluding ligands with more intracyclic heteroatoms or fused aromatic cycles. Overall, the primary goal of this Review is to highlight both old and recent synthetic strategies that find applicability in the mentioned applications. By doing so, the authors hope to establish a first reference for phenanthroline synthesis, covering all possible positions on the backbone, and hope to inspire all concerned chemists to devise new strategies that have not yet been explored.

Molecular Triad Containing a TEMPO Catalyst Grafted on Mesoporous Indium Tin Oxide as a Photoelectrocatalytic Anode for Visible Light-Driven Alcohol Oxidation.

Photoelectrochemical cells based on semiconductors are among the most studied methods of artificial photosynthesis. This study concerns the immobilization, on a mesoporous conducting indium tin oxide electrode (nano-ITO), of a molecular triad (NDADI-P-Ru-TEMPO) composed of a ruthenium tris-bipyridine complex (Ru) as photosensitizer, connected at one end to 2,2,6,6-tetramethyl-1-piperidine N-oxyl (TEMPO) as alcohol oxidation catalyst and at the other end to the electron acceptor naphthalenedicarboxyanhydride dicarboximide (NDADI). Light irradiation of NDADI-P-Ru-TEMPO grafted to nano-ITO in a pH 10 carbonate buffer effects selective oxidation of para-methoxybenzyl alcohol (MeO-BA) to para-methoxybenzaldehyde with a TON of approximately 150 after 1 h of photolysis at a bias of 0.4 V vs. SCE. The faradaic efficiency is found to be of 80±5 %. The photophysical study indicates that photoinduced electron transfer from the Ru complex to NDADI is a slow process and must compete with direct electron injection into ITO to have a better performing system. This work sheds light on some of the important ways to design more efficient molecular systems for the preparation of photoelectrocatalytic cells based on catalyst-dye-acceptor arrays immobilized on conducting electrodes.

Photocathode functionalized with a molecular cobalt catalyst for selective carbon dioxide reduction in water.

Artificial photosynthesis is a vibrant field of research aiming at converting abundant, low energy molecules such as water, nitrogen or carbon dioxide into fuels or useful chemicals by means of solar energy input. Photo-electrochemical reduction of carbon dioxide is an appealing strategy, aiming at reducing the greenhouse gas into valuable products such as carbon monoxide at low or without bias voltage. Yet, in such configuration, there is no catalytic system able to produce carbon monoxide selectively in aqueous media with high activity, and using earth-abundant molecular catalyst. Upon associating a p-type Cu(In,Ga)Se2 semi-conductor with cobalt quaterpyridine complex, we herein report a photocathode complying with the aforementioned requirements. Pure carbon dioxide dissolved in aqueous solution (pH 6.8) is converted to carbon monoxide under visible light illumination with partial current density above 3 mA cm-2 and 97% selectivity, showing good stability over time.

Unveiling 79-Year-Old Ixene and Its BN-Doped Derivative.

Polycyclic aromatic hydrocarbons (PAHs) are key components of organic electronics. The electronic properties of these carbon-rich materials can be controlled through doping with heteroatoms such as B and N, however, few convenient syntheses of BN-doped PAHs have been reported. Described herein is the rationally designed, two-step syntheses of previously unknown ixene and BN-doped ixene (B2 N2 -ixene), and their characterizations. Compared to ixene, B2 N2 -ixene absorbs longer-wavelength light and has a smaller electrochemical energy gap. In addition to its single-crystal structure, scanning tunneling microscopy revealed that B2 N2 -ixene adopts a nonplanar geometry on a Au(111) surface. The experimentally obtained electronic structure of B2 N2 -ixene and the effect of BN-doping were confirmed by DFT calculations. This synthesis enables the efficient and convenient construction of BN-doped systems with extended π-conjugation that can be used in versatile organic electronics applications.

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 µA cm-2 at -0.87 V vs. NHE was obtained, providing a faradaic efficiency of 32% for CO production.

An Indacenodithieno[3,2-b]thiophene-Based Organic Dye for Solid-State p-Type Dye-Sensitized Solar Cells.

An indacenodithieno[3,2-b]thiophene (IDTT) unit is used as a linker moiety to design a new p-type dye-TIP-for solid-state p-type dye-sensitized solar cells. Solar cells based on the TIP dye offered an efficiency of 0.18 % with an open-circuit photovoltage of 550 mV and a short-circuit photocurrent density of 0.86 mA cm-2 , which is better than those of two reference dyes, PB6 and BH4. Charge lifetime experiments reveal that the IDTT linker-based TIP dye significantly suppresses charge recombination losses in the devices.

Correction: Ultrafast dye regeneration in a core-shell NiO-dye-TiO2 mesoporous film.

Correction for 'Ultrafast dye regeneration in a core-shell NiO-dye-TiO2 mesoporous film' by Lei Tian et al., Phys. Chem. Chem. Phys., 2018, 20, 36-40.

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.

Solid state p-type dye sensitized NiO-dye-TiO2 core-shell solar cells.

Solid state p-type dye sensitized NiO-dye-TiO2 core-shell solar cells with an organic dye PB6 were successfully fabricated for the first time. With Al2O3 as an inner barrier layer, the recombination process between injected holes in NiO and injected electrons in TiO2 was significantly suppressed and the charge transport time was also improved.

Ultrafast dye regeneration in a core-shell NiO-dye-TiO2 mesoporous film.

In this study, a core-shell NiO-dye-TiO2 mesoporous film was fabricated for the first time, utilizing atomic layer deposition technique and a newly designed triphenylamine dye. The structure of the film was confirmed by SEM, TEM, and EDX. Excitation of the dye led to efficient and fast charge separation, by hole injection into NiO, followed by an unprecedentedly fast dye regeneration (t1/2 ≤ 500 fs) by electron transfer to TiO2. The resulting charge separated state showed a pronounced transient absorption spectrum caused by the Stark effect, and no significant decay was found within 1.9 ns. This indicates that charge recombination between NiO and TiO2 is much slower than that between the NiO and the reduced dye in the absence of the TiO2 layer (t1/2 ≈ 100 ps).

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 based on mesoporous NiO is synthesized by a facile click reaction for mechanistic studies and application in a dye-sensitized solar fuel device. The system is systematically investigated by photoelectrochemical measurements, density functional theory, time-resolved fluorescence, transient absorption spectroscopy, and 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 process to reduce the catalyst. Moreover, the dye adopts different structures with different excited state energies, and excitation energy transfer occurs between neighboring molecules on the semiconductor surface. The photoelectrochemical experiments also show hydrogen production by this system. 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 system on the photocathode is proposed on the basis of this study.

New dyes for DSSC containing triphenylamine based extended donor: Synthesis, photophysical properties and device performance.

Three new triphenylamine based dyes with Donor-Donor-Spacer-Acceptor (D-D-π-A) arrangement were designed and synthesized by convenient synthetic pathway. Unsymmetrical extended donor part may help to reduce the aggregation of dyes on the semiconductor surface. Wide range of absorption in the visible spectrum, electrochemical studies and theoretical optimization suggest that these dyes can be good members for DSSC. Further to check the performance of these dyes in device the solar cells were developed using iodine free Co-based electrolyte. Electronic characterisation concludes that devices based on D6 have the highest power conversion efficiency (4.7%) mostly due to an improved electron lifetime, which therefore improves both the VOC and JSC of the devices.

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 2 (T-BDO-T), 3 (Se-BDO-Se), 5 (T-BDT-T), and 6 (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 2, 3, 5, and 6 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 2, 3, and 6 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 cm(2) V(-1) s(-1) and Ion/Ioff ratio of 10(4).

Charge delocalization in a homologous series of α,α'-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 (H(AB)) 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.

Twisting (conformational changes)-based selective 2D chalcogeno podand fluorescent probes for Cr(III) and Fe(II).

The fluorenoazomethine containing chalcogeno podand fluorescent probes having N, O/S/Se coordinating donor unit show donor specific 'turn-on' recognition property towards metals (Cr(III), Fe(II) and Cu(II)), where the fluorescence signals are controlled by the conformational change of the ligand framework on binding with the metal ion.