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Anchoring groups play an important role in the assembly of functional molecules onto semiconductor substrates for dye‐sensitized photocatalysis. In addition to directly influencing the adsorption stability, anchoring groups significantly impact the efficiency of electron or hole injection into the substrate, which is a crucial step for photocatalytic reactions. Most reported dye‐sensitized photocatalytic systems, including semiconductor nanoparticles and photoelectrochemical cells, are prepared using the carboxylic or phosphonic acid anchors. The systems prepared with these conventional anchors usually suffer from low adsorption stability in aqueous media. Alternatively, pyridine has emerged as an anchoring group of photosensitizers and molecular catalysts in the construction of photocatalytic systems. The resulting semiconductor nanoparticles and photoelectrodes show superior adsorption stability in aqueous media, providing a simple and efficient way to sensitize the metal or metal oxide substrate. This review focuses on the recent advances of such a pyridine anchoring strategy in the assembly of photosensitizers and molecular catalysts for photocatalytic applications, mainly including photocatalytic water oxidation, reduction, and splitting. The further exploration and understanding of the pyridine‐anchoring method are believed to boost the development of advanced dye‐sensitized photocatalytic devices and technologies. [ABSTRACT FROM AUTHOR]

At present, one of the major factors limiting the further improvement of inverted (p‐i‐n) perovskite solar cells (PSCs) is trap‐assisted non‐radiative recombination at the perovskite/electron transporting layer (ETL) interface. Surface passivation with organic ammonium salt is a powerful strategy to improve the performance of PSCs. Herein, an effective method by using propylamine hydroiodide (PAI) and 1,3‐diaminopropane dihydroiodide (PDADI) is reported to modify the perovskite/ETL interface. These two ammonium salts do not form new perovskite but directly passivate the defects on the perovskite surface after annealing. The results show that the PDADI‐modified perovskite films possess a lower surface defect density and less non‐radiative recombination as well as improved charge carrier transport. Based on this strategy, the PDADI‐modified p‐i‐n PSCs deliver an impressive efficiency of 25.09% (certified 24.58%) with an open‐circuit voltage of 1.184 V. Furthermore, the unencapsulated PDADI‐modified PSCs also exhibit good storage stability, retaining 91% of initial PCE at 65 °C in a N2 glove box for 1300 h. This strategy provides an efficient route to fabricate highly efficient and stable inverted p‐i‐n structured PSCs. [ABSTRACT FROM AUTHOR]

The development of efficient photocathodes is of critical importance for the constructions of promising tandem photo‐electrochemical cells. Most known dye‐sensitized photocathodes are prepared with the conventional carboxylic or phosphonic acid anchors and require the presence of other terminal linking groups to connect catalysts; they suffer from high synthetic difficulty and low adsorption stability in aqueous media. Here, a compact bilayer photocathode has been prepared by using a pyrene‐based photosensitizer with multiple terminal pyridine moieties as both the anchoring and linking groups to connect a Co hydrogen‐evolution catalyst to the NiO substrate. The catalyst and dye molecule are assembled in a layer‐by‐layer manner on NiO through the metal‐pyridine coordination. This photocathode exhibits good dye adsorption stability in aqueous media. A stable cathodic photocurrent of 70 μA cm−2 was achieved, with H2 being generated at the photocathode under the visible‐light irradiation. The Faraday efficiency of H2 evolution was estimated to be 9.1 %. Transient absorption spectral studies suggest that the interfacial hole transfer occurs within a few picoseconds. The integration of the organic photosensitizer with pyridine anchoring and linking groups is expected to provide a simple method for the fabrication of stable and efficient photocathodes. [ABSTRACT FROM AUTHOR]

The development of circularly polarized electroluminescence (CPEL) is currently hampered by the high difficulty and cost in the syntheses of suitable chiral materials and the notorious chirality diminishment issue in electrical devices. Herein, diastereomeric IrIII and RuII complexes with chiral (±)‐camphorsulfonate counteranions are readily synthesized and used as the active materials in circularly polarized light‐emitting electrochemical cells to generate promising CPELs. The addition of the chiral ionic liquid (±)‐1‐butyl‐3‐methylimidazole camphorsulfonate into the active layer significantly improves the device performance and the electroluminescence dissymmetry factors (≈10−3), in stark contrast to the very weak circularly polarized photoluminescence of the spin‐coated films of these diastereomeric complexes. Control experiments with enantiopure IrIII complexes suggest that the chiral anions play a dominant role in the electrically‐induced amplification of CPELs. [ABSTRACT FROM AUTHOR]

Elpasolite Cs2AgBiBr6 also known as double perovskite has been touted in recent years as a promising alternative to the lead‐based perovskite for light harvesting. Its structure and properties mainly stem from the replacement of Pb2+ cation with a pair of aliovalent silver (Ag+) and bismuth (Bi3+) cations. Although the elpasolite Cs2AgBiBr6 exhibits improved stability, its photophysical properties and device performance are inferior to those of the Pb‐based perovskites. To date, numerous efforts have been geared toward the development of efficient Cs2AgBiBr6 solar cells. However, the indirect, wide bandgap and high exciton binding energy of Cs2AgBiBr6 have limited such efforts. This has been attributed to its low (zero) electronic dimensionality (0D), formation of small polaronic states, and interfacial imperfections with charge transporting layers. In this review, the different aspects of the elpasolite Cs2AgBiBr6 in relation to compositional and interlayer interactions in solar cell are discussed, and its suitability for photovoltaic application is assessed, accompanied by potential measures to further advance its performance. An alternate application of Cs2AgBiBr6 in photocatalysis, which takes advantage of its less toxicity and better stability, is also discussed. [ABSTRACT FROM AUTHOR]

Nano‐ and micromaterials with anisotropic photoluminescence and photon transport have widespread application prospects in quantum optics, optoelectronics, and displays. But the nature of the polarization information of the out‐coupled light, with respect to that of the source luminescence, has never been explored in active optical‐waveguiding organic crystals. Herein, three different modes (selective, anisotropic, and consistent) of polarized‐photon out‐coupling are proposed and successfully implemented in a set of 2D organic microcrystals with highly linearly‐polarized luminescence. It is found that the polarization direction and degree of the luminescence out‐coupled through different waveguiding channels can either be essentially retained or distinctly changed with respect to those of the original luminescence, depending on the molecular arrangement and the orientation of transition dipole moments of the crystal. This work demonstrates the promising potential of 2D emissive microcrystals in multi‐channel polarized photon transport. [ABSTRACT FROM AUTHOR]

Inorganic cesium lead halide perovskites offer a pathway towards thermally stable photovoltaics. However, moisture‐induced phase degradation restricts the application of hole transport layers (HTLs) with hygroscopic dopants. Dopant‐free HTLs fail to realize efficient photovoltaics due to severe electrical loss. Herein, we developed an electrical loss management strategy by manipulating poly(3‐hexylthiophene) with a small molecule, i.e., SMe‐TATPyr. The developed P3HT/SMe‐TATPyr HTL shows a three‐time increase of carrier mobility owing to breaking the long‐range ordering of "edge‐on" P3HT and inducing the formation of "face‐on" clusters, over 50 % decrease of the perovskite surface defect density, and a reduced voltage loss at the perovskite/HTL interface because of favorable energy level alignment. The CsPbI2Br perovskite solar cell demonstrates a record‐high efficiency of 16.93 % for dopant‐free HTL, and superior moisture and thermal stability by maintaining 96 % efficiency at low‐humidity condition (10–25 % R. H.) for 1500 hours and over 95 % efficiency after annealing at 85 °C for 1000 hours. [ABSTRACT FROM AUTHOR]

A simple and general method is presented herein for the in situ preparations of circularly polarized luminescence (CPL)‐active microcrystals with a large luminescence dissymmetry factor glum, high fluorescence quantum efficiency (ΦFL), wide emission color tenability, and well‐ordered morphology. The reactions of pyridine‐containing achiral molecules 1–7 with chiral camphor sulfonic acid ((±)‐CSA) gave crystalline microplates formed by hydrogen bonding interactions between the protonated pyridinium units and the sulfonic anions. The chiral information of CSA are effectively transferred to the microcrystals by hydrogen bonding to afford full‐color CPL from deep‐blue to red with glum in the order of 10−2 and ΦFL up to 80 %. Moreover, organic microcrystals with high‐performance white CPL (ΦFL=46 %; |glum|=0.025) are achieved via the light‐harvesting energy transfer between blue and yellow emitters. [ABSTRACT FROM AUTHOR]

Summary of main observation and conclusion: A star‐shaped compound 1 with a pyrene core and four triarylamine arms has been prepared and characterized. It exhibits intense intramolecular‐charge‐transfer (ICT) emissions with strong solvatofluorochromism. On the basis of the temperature‐dependent emission color and wavelength changes, compound 1 behaves as a fluorescent thermometer between 200 and 400 K with a high theromosensitivity. In comparison, model compounds with one or two triarylamine arms show distinctly lower thermosensitivity. [ABSTRACT FROM AUTHOR]

A star‐shaped N C N‐pincer tri‐RuII complex 3 with a triarylamine core, capped with three 2,2':6',2''‐terpyridine‐4,4',4''‐tricarboxylic acid terminal ligands, has been synthesized. The single‐crystal X‐ray structure of a precursor ester complex 7 is presented. By using the Zr‐mediated layer‐by‐layer assembly, multilayer films FTO/SnO2:Sb/(3)n(Zr)n‐1 (n = 1–4) have been prepared on Sb‐doped SnO2 nanocrystalline substrates. These films have been characterized by XPS and SEM analysis. The electrochromism of these films in the near‐infrared region were examined by oxidative spectroelectrochemical measurements and douple‐potential‐step chronoamperometry. The two‐layered film displays the best overall performance with a contrast ratio (ΔT%) of 36 % at 1550 nm and response time of shorter than 2 s. After 1000 switching cycles, around 11 % loss of the contrast ratio is observed, suggesting good cyclic stability of these films. In addition, a comparison of the electrochromic performance of these multilayer films with respect to the previously reported electropolymerized films of a related tri‐RuII complex and monolayer films of two mono‐RuII complexes on SnO2:Sb is presented. [ABSTRACT FROM AUTHOR]

Abstract: A readily available small molecular hole‐transporting material (HTM), OMe‐TATPyr, was synthesized and tested in perovskite solar cells (PSCs). OMe‐TATPyr is a two‐dimensional π‐conjugated molecule with a pyrene core and four phenyl‐thiophene bridged triarylamine groups. It can be readily synthesized in gram scale with a low lab cost of around US$ 50 g−1. The incorporation of the phenyl‐thiophene units in OMe‐TATPyr are beneficial for not only carrier transportation through improved charge delocalization and intermolecular stacking, but also potential trap passivation via Pb–S interaction as supported by depth‐profiling XPS, photoluminescence, and electrochemical impedance analysis. As a result, an impressive best power conversion efficiency (PCE) of up to 20.6 % and an average PCE of 20.0 % with good stability has been achieved for mixed‐cation PSCs with OMe‐TATPyr with an area of 0.09 cm2. A device with an area of 1.08 cm2 based on OMe‐TATPyr demonstrates a PCE of 17.3 %. [ABSTRACT FROM AUTHOR]

Abstract: A readily available small molecular hole‐transporting material (HTM), OMe‐TATPyr, was synthesized and tested in perovskite solar cells (PSCs). OMe‐TATPyr is a two‐dimensional π‐conjugated molecule with a pyrene core and four phenyl‐thiophene bridged triarylamine groups. It can be readily synthesized in gram scale with a low lab cost of around US$ 50 g−1. The incorporation of the phenyl‐thiophene units in OMe‐TATPyr are beneficial for not only carrier transportation through improved charge delocalization and intermolecular stacking, but also potential trap passivation via Pb–S interaction as supported by depth‐profiling XPS, photoluminescence, and electrochemical impedance analysis. As a result, an impressive best power conversion efficiency (PCE) of up to 20.6 % and an average PCE of 20.0 % with good stability has been achieved for mixed‐cation PSCs with OMe‐TATPyr with an area of 0.09 cm2. A device with an area of 1.08 cm2 based on OMe‐TATPyr demonstrates a PCE of 17.3 %. [ABSTRACT FROM AUTHOR]

Three tris(bidentate) monoruthenium complexes [Ru(dpma)(bpy)2](PF6)2 [1(PF6)2; dpma = di(pyrid-2-yl)(methyl)- amine, bpy = 2,2'-bipyridine], [Ru(dpma)2(bpy)](PF6)2 [2(PF6)2], and [Ru(dpma)3](PF6)2 [3(PF6)2] with the electron-rich ligand dpma were synthesized and characterized. The single-crystal Xray structures of 1(PF6)2 to 3(PF6)2 are presented. The electrochemical and spectroscopic properties of these complexes were examined and compared with those of the reference complex [Ru(bpy)3](PF6)2. Complexes 1(PF6)2 to 3(PF6)2 show a decreased RuIII/II redox potential by 140-310 mV with respect to [Ru(bpy)3](PF6)2. The strong emission property of [Ru(bpy)3]- (PF6)2 is maintained in 1(PF6)2 and 2(PF6)2. However, complex 3(PF6)2 is only weakly emissive at room temperature. In addition, density functional theory (DFT) and time-dependent DFT calculations were performed to complement these experimental results. [ABSTRACT FROM AUTHOR]

A series of cyclometalated diruthenium complexes with a redox-active amine bridge were synthesized. Depending on the terminal ligands of the ruthenium components and the substituent on the amine unit, the one-electron-oxidized state can be either in the form of a weakly or strongly coupled mixed-valence diruthenium complex, a fully charge-delocalized three-center system, or a bridge-biased electrophore. This transition among different electronic forms was supported by electrochemistry, near-infrared absorption, electron paramagnetic resonance, and density functional theory analysis. [ABSTRACT FROM AUTHOR]

Six cyclometalated diruthenium complexes bridged by 3,3′,5,5′-tetra(pyrid-2-yl)biphenyl have been prepared, in which 12+, 32+, and 52+ are symmetric complexes with different terminal ligands [2,6-bis( N-methylbenzimidazolyl)pyridine (Mebip), 4′-tolyl-2,2′:6′,2″-terpyridine (ttpy), and trimethyl-4,4′,4″-tricarboxylate-2,2′:6′,2″-terpyridine (Me3tctpy), respectively]. Three other complexes with mixed terminal ligands (Mebip-Me3tctpy for 62+; Mebip-ttpy for 72+; ttpy-Me3tctpy for 82+) are structurally nonsymmetric. These complexes display two consecutive Ru(III/II) redox couples between 0.20 and 0.90 V vs. Ag/AgCl, with the potential splitting ranging from 150 (for 52+) to 280 mV (for 62+). The mixed-valent states of these complexes have been generated by stepwise electrolysis. The symmetric complexes show intervalence charge transfer (IVCT) transitions at similar energy ( Eop ≈ 5750 cm-1), with the electronic coupling parameter Vab of 1240, 1220, and 970 cm-1 for 13+, 33+, and 53+, respectively. The nonsymmetric series show significantly different Eop (7600, 5850, and 6650 cm-1 for 63+, 73+, and 83+, respectively) but Vab values that were comparable to that of 13+. DFT and TDDFT calculations have been performed to complement these experimental results. [ABSTRACT FROM AUTHOR]

Monoamine 1, diamines 2- 4, triamine 5, and tetraamine 6 have been synthesized by substituting dianisylamino groups at the 1-, 3-, 6-, and/or 8-positions of pyrene. Diamines 2- 4 differ in the positions of the amine substituents. No pyrene-pyrene interactions are evident in the single-crystal packing of 3, 4, and 6. With increasing numbers of amine substituents, the first oxidation potential decreases progressively from the mono- to the tetraamine. These compounds show intense charge-transfer (CT) emission in CH2Cl2 at around 530 nm with quantum yields of 48-68 %. Upon stepwise oxidation by electrolysis or chemical oxidation, these compounds were transformed into radical cations 1⋅+- 6⋅+ and dications 22+- 62+, which feature strong visible and near-infrared absorptions. Time-dependent density functional theory studies suggested the presence of localized transitions from the pyrene radical cation and aminium radical cation, intervalence CT, and CT between the pyrene and amine moieties. Spectroscopic studies indicated that these radical cations and dications have good stability. Triamine 5 and tetraamine 6 formed efficient CT complexes with tetracyanoquinodimethane in solution. The results of EPR spectroscopy and density functional theory calculations suggested that the dications 22+- 42+ have a triplet ground state, whereas 52+ and 62+ have a singlet ground state. The dication of 1,3-disubstituted diamine 4 exhibits a strong EPR signal. [ABSTRACT FROM AUTHOR]

Nine cyclometalated ruthenium complexes with a redox-active diphenylamine unit in the para position to the RuC bond were prepared. MeO, Me, and Cl substituents on the diphenylamine unit and three types of auxiliary ligands-bis( N-methylbenzimidazolyl)pyridine (Mebip), 2,2′:6′,2′′-terpyridine (tpy), and trimethyl-4,4′,4′′-tricarboxylate-2,2′:6′,2′′-terpyridine (Me3tctpy)-were used to vary the electronic properties of these complexes. The derivative with an MeO-substituted amine unit and Me3tctpy ligand was studied by single-crystal X-ray analysis. All complexes display two well-separated redox waves in the potential region of +0.1 to +1.0 V versus Ag/AgCl, and the potential splitting ranges from 360 to 510 mV. Spectroelectrochemical measurements show that these complexes display electrochromism at low potentials and intense near-infrared (NIR) absorptions. In the one-electron oxidized form, the complex with the Cl-substituted amine unit and Mebip ligand shows a moderate ligand-to-metal charge transfer at 800 nm. The other eight complexes show asymmetric, narrow, and intense intervalence charge-transfer transitions in the NIR region, which are independent of the polarity of the solvent. The Mebip-containing complexes display rhombic or broad isotropic EPR signals, whereas the other seven complexes show relatively narrow isotropic EPR signals. In addition, DFT and time-dependent DFT studies were performed to gain insights into the spin distributions and NIR absorptions. [ABSTRACT FROM AUTHOR]

A common bridging ligand, 3,3′,5,5′-tetrakis( N-methylbenzimidazol-2-yl)biphenyl, and four terpyridine terminal ligands with various substituents (amine, tolyl, nitro, and ester groups) have been used to synthesize ten cyclometalated diruthenium complexes 12+- 102+. Among them, compounds 12+- 62+ are redox nonsymmetric, and others are symmetric. These complexes show two RuIII/II processes and an intervalence charge transfer (IVCT) transition in the one-electron oxidized state. The potential separation (Δ E) of 12+- 102+ has been correlated to the energy difference Δ G0, the energy of the IVCT band Eop, and the ground-state delocalization coefficient α2. Time-dependent (TD)DFT calculations suggest that the absorptions in the visible region of 12+- 62+ are mainly associated with the metal-to-ligand charge-transfer transitions from both ruthenium ions and to both terminal ligands and the bridging ligand. However, the energies of these transitions vary significantly. DFT calculations have been performed on 12+- 62+ and 13+- 63+ to give information on the electronic structures and spin populations of the mixed-valent compounds. The TDDFT-predicted IVCT excitations reproduce well the experimental trends in transition energies. In addition, three monoruthenium complexes have been synthesized for a comparison study. [ABSTRACT FROM AUTHOR]

Four heterodimetallic complexes [Ru(Fcdpb)(L)](PF6) (Fcdpb=2-deprotonated form of 1,3-di(2-pyridyl)-5-ferrocenylbenzene; L=2,6-bis-( N-methylbenzimidazolyl)-pyridine (Mebip), 2,2′:6′,2′′-terpyridine (tpy), 4-nitro-2,2′:6′,2′′-terpyridine (NO2tpy), and trimethyl-4,4′,4′′-tricarboxylate-2,2′:6′,2′′-terpyridine (Me3tctpy)) have been prepared. The electrochemical and spectroelectrochemical properties of these complexes have been examined in CH2Cl2, CH3NO2, CH3CN, and acetone. These complexes display two consecutive redox couples owing to the stepwise oxidation of the ferrocene (Fc) and ruthenium units, respectively. The potential difference, Δ E1/2 ( E1/2(RuII/III)− E1/2(Fc0/+)), decreased slightly with increasing solvent donocity. The mixed-valent states of these complexes have been generated by and the resulting intervalence charge-transfer (IVCT) bands have been analyzed by Hush theory. Good linear relationships exist between the energy of the IVCT band, Eop, and Δ E1/2 of four mixed-valent complexes in a given solvent. [ABSTRACT FROM AUTHOR]

Summary of main observation and conclusion: A star‐shaped compound 1 with a pyrene core and four triarylamine arms has been prepared and characterized. It exhibits intense intramolecular‐charge‐transfer (ICT) emissions with strong solvatofluorochromism. On the basis of the temperature‐dependent emission color and wavelength changes, compound 1 behaves as a fluorescent thermometer between 200 and 400 K with a high theromosensitivity. In comparison, model compounds with one or two triarylamine arms show distinctly lower thermosensitivity. [ABSTRACT FROM AUTHOR]

Review: 76 refs. [ABSTRACT FROM AUTHOR]