A square-planar nickel(II) dithiolate complex is an active molecular catalyst for both photoreduction of protons from water with a turnover number (>1500) and electroreduction of protons from weakly acidic solutions with remarkable turnover frequencies (5575 s−1 at −1.92 V and 1441 s−1 at −1.61 V vs. SCE). DFT calculations provide in-depth insight into the catalytic cycle of the electrochemical reaction, suggesting that the sulfur atoms play crucial roles in proton exchange and hydrogen formation.

•Phthalocyanine cobalt is an efficient photocatalyst for H2 production with a photosensitizer [RuII(bpy)3]Cl2.•The photocatalyst gives up to 2400 TON with an initial TOF 680 TON h−1.•The efficiency and stability of the photocatalyst is superior to the reported porphyrin cobalt.In this contribution, we report an efficient homogeneous system for the visible light-driven H2 production from aqueous protons. This comprises a macrocyclic phthalycyanine cobalt complex [CoIIPc(-2)] as a hydrogen-evolving catalyst (HEC), [RuII(bpy)3]Cl2 (bpy = 2,2′-bipyridine) as a photosensitizer (PS) and triethylamine (TEA) as a sacrificial electron donor (SED). The system gives up to 2400 TON versus the catalyst with an initial TOF as high as 680 TON h−1. Phthalocyanine cobalt and its derivatives are a promising new direction for molecular catalysts readily accessible in a large scale and low-cost achieving the photogeneration of H2.Phthalocyanine cobalt is confirmed as highly efficient molecular catalyst of light-driven H2 production when coupled with [RuII(bpy)3]Cl2 (bpy = 2,2′-bipyridine) as a photosensitizer and triethylamine as a sacrificial electron donor.Download high-res image (207KB)Download full-size image

•A D-π-A-π-A based organic dye has been successfully synthesized and characterized.•The dye showed a multifunctional property in both DSC and solar fuel generator.•The dye showed better performance in the light-to-fuel conversion.A novel metal-free D-π-A-π-A based organic photosensitizer, with carbazole as electron donor; benzothiadiazole as auxiliary electron withdrawing unit; acetylene and benzene as linker; and cyanoacrylic acid as anchoring group, has been successfully synthesized and effectively employed in the development of solar energy conversion of photovoltaic devices and solar hydrogen generation. In the solar energy conversion systems, comparisons were made with a simple reference D-π-A sensitizer. The results show that the new D-π-A-π-A dye has greater potential in the light-to-fuel conversion (ΦH2 = 5.56% for the new dye vs ΦH2 = 0.12% for the reference dye) than light-to-electricity conversion (η = 3.50% for the new dye vs 1.14% for the reference dye).

A noble-metal-free molecular dyad was constructed by anchoring a thienyl-expanded BODIPY photosensitizer (PS) to a cobaloxime catalyst, which gives a 2.5-fold increase in the TON, and a 3-fold enhancement in the quantum efficiency as compared to the multicomponent catalytic system for the generation of hydrogen via the reduction of water. The stability of PS was expected to improve by introducing the thienyl moiety into the BODIPY core.

A series of boron dipyrromethene (BODIPY) dyes (B1–B5) having H atoms at 2,6-positions or heavy-atom I at 2-/2,6-positions, and an ortho- or a para-COOH substituted phenyl moiety at the 8-position on the BODIPY core were synthesized and characterized. These organic dyes were applied for investigating the relationship between the BODIPY structure and the effectiveness of homogeneous and heterogeneous visible-light-driven hydrogen production as well as dye-sensitized solar cells (DSSCs). For the homogeneous photocatalytic hydrogen production systems with a cobaloxime catalyst, the efficiency of hydrogen production could be tuned by substituting with heavy atoms and varying carboxyl group orientations of BODIPYs. As a result, B5 containing two I atoms and an ortho-COOH anchoring group was the most active one (TONs = 197). The activity of hydrogen generation followed the order B5 > B3 > B2 > B1 = B4 = 0. An interesting “ortho-position effect” was observed in the present homogeneous systems, i.e., substitution groups were located at the ortho-position and higher hydrogen production activities were obtained. For the heterogeneous hydrogen production systems with a platinized TiO2 catalyst, the effectiveness of hydrogen evolution was highly influenced by the intersystem crossing efficiency, molar absorptivity and positions of the anchoring group of dyes. Thus, B3 having two core iodine atoms and a para-COOH group with TONs of 70 excelled other BODIPYs and the TONs of hydrogen generation showed the trend of B3 > B5 > B2 > B1 = B4 = 0. The results demonstrate that the present photocatalytic H2 production proceeds with higher efficiency and stability in the homogeneity than in the heterogeneity. In the case of DSSCs, the overall cell performance of BODIPY chromophores was highly dependent on both the absence or the presence of iodine atoms on the BODIPY core and –COOH anchoring positions. The B1–TiO2 system showed the best cell performance, because the most effective surface binding mode is allowed with this structure. This is also in contrast with the case of dye-sensitized solar H2 generation, in which B3 was the most efficient chromophore. The differences between dye-sensitized hydrogen-generating systems and DSSCs may be due to rates of electron transfer and the dye aggregation tendency.

•One novel 2D copper(II) coordination polymer was synthesized and characterized.•A planar water hexamer was trapped in the interstitial void of the coordination polymer.•The formation of water hexamer is reversible by straightforward processes of dehydration/rehydration.Coordination polymeric solid, {[Cu(btec)0.5(bpe)(H2O)2]⋅(H2O)4}n (1) (H4btec = 1,2,4,5-benzenetetracarboxylic acid, and bpe = 1,2-bis(4-pyridyl)ethane), has been obtained by the solution phase ultrasonic synthesis techniques. The structure established through X-ray structural analysis shows that a centrosymmetric water hexamer with planar conformation structurally similar to aromatic benzene is unambiguously crystallized within the hydrophilic channel of 1. Water escapes at 150 °C but is re-absorbed using water vapor. The reversible formation of this water cluster was supported from powder X-ray diffraction (PXRD), FTIR spectra and TGA/DTA. The reversible dehydration/rehydration behaviors enable analysis of the nature of the intermolecular interactions that occur between the planar hexameric water and the resulting host framework. When the auxiliary ligand bpe was removed from the synthetic conditions, another complex {[Cu(btec)0.5(H2O)3]⋅H2O}n (2) only encapsulating a water dimer was afforded, which suggests bpe plays an important role in the formation of the framework and water clusters.The reversible formation of a centrosymmetric planar water hexamer is within the crystal host of {[Cu(bpe)(btec)0.5(H2O)2]⋅(H2O)4}n (1).

A simple 4-aniline boron-dipyrromethene (BODIPY) dye (1) was developed as a highly sensitive acidic pH fluorescent probe excitable with visible light based on a photoinduced electron transfer (PeT) mechanism. The pH titration indicates that the fluorescence intensity increases more than 500-fold within the pH range of 4.12–1.42 with a pKa value of 3.24 in methanol–water (1:1, v/v) solution, which is valuable for studying strongly acidic conditions. Density functional theory (DFT) calculations reproduce the fluorescence off–on behavior. 1 has also been used as a fluorescent chemosensor for the visual detection of dissolved carbon dioxide (CO2) gas. The underlying mechanism of the sensing process is rationalized. This probe can be recovered by bubbling nitrogen (N2) gas into CO2-treated solutions for over 10 cycles. In addition, two logic gates (OR and INH) have been achieved at the molecular level by changing the initial states of system 1 and chemical inputs.

In this study a series of supramolecular BODIPY–cobaloxime systems Co-Bn (n = 1–4): [{Co(dmgH)2Cl}{4,4-difluoro-8-(4-pyridyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene}] (Co-B1), [{Co(dmgH)2Cl}{4,4-difluoro-8-(4-pyridyl)-1,3,5,7-tetramethyl-2,6-diiodo-4-bora-3a,4a-diaza-s-indacene}] (Co-B2), [{Co(dmgH)2Cl}{4,4-difluoro-8-(3-pyridyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene}] (Co-B3), and [{Co(dmgH)2Cl}{4,4-difluoro-8-(3-pyridyl)-1,3,5,7-tetramethyl-2,6-diiodo-4-bora-3a,4a-diaza-s-indacene}] (Co-B4) (BODIPY = boron dipyrromethene, dmgH = dimethylglyoxime) have been synthesized by replacing one axial chlorine of cobaloxime moieties with the pyridine residues of BODIPYs, and structurally characterized. Absorption spectra show that the optical properties of the BODIPY–cobaloximes are essentially the sum of their constituent components, indicating weak interactions between the cobaloxime units and BODIPY chromophores in the ground state. If any, electronic communications may take place through the intramolecular electron transfer across their orthogonal structures. The possibility of intramolecular electron transfer is further supported by the results of the density functional theory (DFT) calculations at UB3LYP/LANL2DZ levels on Co-B2˙− and Co-B4˙−, which show that the highest occupied molecular orbitals (HOMOs) possess predominantly BODIPY character, while the lowest unoccupied molecular orbitals (LUMOs) are located on the cobalt centers. The HOMO → LUMO transition is an electron-transfer process (BODIPY˙− radical anions → cobaloxime fragments). In view of the possible occurrence of electron transfer, these noble-metal-free BODIPY–cobaloximes are studied as single-component homogeneous photocatalysts for H2 generation in aqueous media. Under optimized conditions, the 2,6-diiodo BODIPY-sensitized cobaloxime Co-B4 that contains a meta-pyridyl at the 8-position of BODIPY presents excellent H2 photoproduction catalytic activity with a turnover number (TON) of 85, which is comparable to that of its analogue Co-B2 that has a para-pyridyl attached onto 2,6-diiodo BODIPY (TON = 82); however, both of the noniodinated BODIPY-sensitizer cobaloximes (Co-B1, Co-B3) exhibit a complete lack of activity under the same experimental conditions. These results show that the presence of heavy atoms in the core of BODIPY is essential for the catalytic process and reductive quenching pathways (namely, the intramolecular electron transfers from BODIPY˙− species to the cobalt centers) for these photocatalytically active systems of Co-Bn (n = 2 and 4) are thermodynamically feasible for the hydrogen-evolving reaction.

In this study we report about two novel azomethine–BODIPY dyads 1 and 2. The two dyads have been, respectively, synthesized by covalent tethering of tautomeric ortho-hydroxy aromatic azomethine moieties including N-salicylideneaniline (SA) and N-naphthlideneaniline (NA) to a BODIPY fluorophore. Both of the two dyads 1 and 2 show enol-imine (OH) structures dominating in the crystalline state. Dyad 1 in the enol state is the most stable form at room temperature in most media, while enol–keto prototropic tautomerism of the NA moiety in solution is preserved in dyad 2, which can be reversibly converted between enol and keto forms in the environment's polarity. Visible illumination of dyad 2 in the enol state excites selectively the BODIPY fragment and then deactivates radiatively by emitting green light in the form of fluorescence, while the emission intensity of 2 in the keto state is quenched on the basis of the proton-coupled photoinduced electron transfer (PCPET) mechanism. This allows large fluorescence modulation between the two states of dyad 2 and generates a novel tautomerisable fluorescent switch. Theoretical calculations including calculated energies, potential energy surfaces (PESs) and intrinsic reaction coordinate (IRC) analysis further support that the single proton transfer reaction from an enol form to a transition state (TS) and from the TS to a keto form for 2 is easier to occur than that for 1, which accounts for the fluorescence quenching of 2 in methanol. The agreement of the experimental results and theoretical calculations clearly suggests that fluorescent and tautomeric components can be paired within the same molecular skeleton and the proton tautomerization of the latter can be designed to regulate the emission of the former. In addition, preliminary experiments revealed that 1 can be potentially used as a simple on/off fluorescent chemosensor which exhibited higher selectivity for Cu2+ over other common cations.

•Two different polymorphic water clusters were trapped in two silver-based complexes.Two sandwich-like frameworks with Ag(I) and mixed ligands, [Ag3(bpp)3(ctc)·16H2O]n (1) and [Ag3(bpe)3(btc)·12H2O]n (2) (where bpp = 1,3-bis(4-pyridyl)propane, H3ctc = 1,3,5-cyclohexanetricarboxylic acid, bpe = 1,2-bis(4-pyridyl)ethane, and H3btc = 1,2,4-benzenetricarboxylic acid), have been synthesized and structurally characterized. Fully deprotonated tricarboxylate ctc3 − in 1 or btc3 − in 2, serves as anionic template driving more water molecules to aggregate into different morphologies of polymeric clusters. In 1, the hydrogen-bonding association of sixteen lattice water molecules leads to the formation of 2D layered water, which is composed of three kinds of units including planar (H2O)4, ladder-like (H2O)8 and windmill-shaped (H2O)20 cluster. One novel 1D double-comb-like water aggregate constructed from alternating (H2O)22 cluster and water dimmer exists in 2. The present observations suggest that anionic templates with more carboxylate groups have high tendency of being hydrated and make polymeric clusters possible.By employing tricarboxylate as anionic templates, we trap and characterize two different polymorphic water clusters including an infinite 2D-layered water and 1D double-comb-like water aggregate in two silver-based coordination polymers.

4-Methoxycarbonylphenyl-substituted BODIPY (boron-dipyrromethene) dye gives, in the solid state, three polymorphs. In spite of the absence of any strong intermolecular interactions in all crystalline forms, the three polymorphs show different photoluminescence properties. This behavior highlights the importance of molecular arrangements of the BODIPY moieties in the crystalline state in perturbing their photophysical properties.

Two novel hydrated adipate dianions including (adip)aaa·(H2O)16 and (adip)gag·(H2O)20 (adip = dianion of adipic acid, aaa = anti–anti–anti and gag = gauche–anti–gauche) were observed in two silver-based cationic hosts. They not only reveal the precise arrangement of water clusters around the carboxylate groups and aliphatic chains of adipate dianions, but show the conformational change of adipate dianions in water clusters, for the first time.

Two kinds of discrete water clusters, acyclic water tetramer and larger (H2O)28 cluster with a novel topknot-shaped (H2O)24 core formed from lattice water molecules, are captured in the voids of a Ag(I) polymeric solid [Ag4(bpda)2(bpp)4·18H2O]n (1) (where bpp = 1,3-bis(4-pyridyl)propane and H2bpda = 1,1′-biphenyl-2,2′-dicarboxylate acid). The centrosymmetric (H2O)24 cluster is basically an assembly of two (H2O)12 subunits and each subunit (H2O)12 has the shape of cage-like water monodecamer hydrogen bonded to one water monomer. The lattice of a crystal host provides two different sizes of hydrophilic environments for stabilizing these clusters. Moreover, the thermogravimetric curve and photoluminescence spectra of 1 were discussed. 1 exhibits strong photoluminescence maximized at 495 nm upon 390 nm excitation at ambient temperature, of which the CIE chromaticity ordinate (x = 0.23, y = 0.42) is close to that of the green component.Acyclic tetrameric and (H2O)28 cluster with a topknot-shaped (H2O)24 core are captured in a Ag(I) polymeric solid. The (H2O)24 cluster is an assembly of two (H2O)12 subunits related by a center of symmetry and each subunit (H2O)12 has the shape of cage-like water mono-decamer hydrogen bonded to one water monomer.Highlights► Acyclic tetrameric and (H2O)28 cluster are captured in the voids of a Ag(I) complex. ► (H2O)28 cluster can be viewed as one topknot-shaped (H2O)24 unit and four dangling water molecules. ► The complex emits luminescence at 495 nm as excited by 390 nm wavelength. ► CIE chromaticity ordinate of the emission is close to that of edge of green component.

A mixed-ligand Ag(I) coordination polymer {[Ag2(bpe)2(H2O)2](chd)·5H2O}n (1) (bpe = 4,4′-bipyridylethylene, H2chd = 1,4-cyclohexanedicarboxylic acid), has been synthesized and structurally characterized. Complex 1 exhibits a three-dimensional (3-D) supramolecular sandwich architecture that is composed of cationic chains of Ag(I) ions and bpe ligands, alternating with anionic sheets in which uncoordinated chd2 − anions and water molecules form a 2-D hydrogen-bonded network. An odd-numbered (H2O)7 cluster is trapped inside the water-chd aggregation. The discrete water heptamer consists of a puckered pentameric core and two pendent water molecules and structurally shows similarity to the simple hydrocarbon (1,1)-dimethylcyclopentane.A discrete and odd-numbered (H2O)7 cluster which consists of a puckered water pentamer and two dangling water molecules and shows a similar to the simple hydrocarbon (1,1)-dimethylcyclopentane, is unambiguously trapped in a Ag(I) mixed-ligand coordination polymer {[Ag2(bpe)2(H2O)2](chd)·5H2O}n (1) (bpe = 4,4′-bipyridylethylene, H2chd = 1,4-cyclohexanedicarboxylic acid).Highlights► One novel Ag(I) complex was synthesized and characterized. ► The complex contains a 2D hydrogen-bonded water-chd aggregation based on odd-numbered (H2O)7 clusters. ► The (H2O)7 cluster consists of a puckered water pentamer and two dangling water molecules. ► The (H2O)7 cluster shows similarity to the simple hydrocarbon (1,1)-dimethylcyclopentane.

The ultrasonic reaction of Ag2O, 1,3-bis(4-pyridyl)propane (bpp) and Na2B4O5(OH)4·8H2O (borax) under ammoniacal medium gave rise to an unexpected 3D Ag(I) supramolecular sandwich lamellar framework, {[Ag2(bpp)2(H2O)2]·[(H3BO3)3(CO3)·2H2O]}n (1), which consists of 2D silver-bpp cationic host and water–borate–carbonate anionic guest layers. The present 2D anionic layer is formed by fused H2O–H3BO3–CO32 − anionic rosette ribbons, in which H3BO3 is obtained via in situ hydrolysis of borax and CO32 − derived from absorption of CO2 in air. Interestingly, an unprecedented [CO32 −·3(H3BO3)] hydrogen-bonding aggregate having the shape of one concave three-leaved propeller is found in the anionic rosette ribbon.The title compound features a 3D supramolecular sandwich architecture that consists of 2D silver-bpp cationic layers and water-borate-carbonate anionic layers. The anionic layer is formed by fused H2O–H3BO3–CO32 − anionic rosette ribbons. The first hydrogen-bonding aggregate [CO32 −·3(H3BO3)] shaped-like one concave three-leaved propeller is found in the anionic layer.Highlights► The Ag(I) compound containing the H2O–H3BO3–CO32− anionic rosette ribbons was synthesized. ► The first [CO32−·3(H3BO3)] hydrogen-bonding aggregate is found in the compound.

An octameric water moiety which consists of a chairlike water hexamer and two pendent water molecules in the 1,4-diaxial positions and shows a similar structure to the hydrocarbon (1r,4r)-1,4-dimethylcyclohexane, is unambiguously trapped in a 2D Cu(II) mixed-ligand coordination polymer, {[Cu2(bpp)2(H2O)2(bpda)2]·6H2O}n (1) (bpp = 1,3-bis(4-pyridyl)propane and H2bpda = 2,2′-biphenyldicarboxylic acid). The water octamer can be extended into a hybrid carboxylate-water decamer when carboxylic oxygen atoms from bpda2− are involved. Interestingly, the present hybrid decamer bears a similar structural topology to a butterfly (H2O)10 cluster. The reversible dehydration/hydration of 1 is determined by X-ray powder diffraction studies.

A discrete centrosymmetric (H2O)20(CH3OH)4 binary cluster was confined in the cavity of a metal-ligand hybrid [Ag4(bpda)2(bpp)4·14H2O·2CH3OH]n (1) (where bpp = 1,3-bis(4-pyridyl)propane and H2bpda = 2,2′-biphenyldicarboxylic acid). The novel mixed water-methanol cluster consists of one grail-shaped hexadecameric cluster, four dangling water and four hanging methanol molecules. The (H2O)16 cluster is composed of two pairs of edge-sharing (H2O)5 rings attached to one (H2O)4 core with twenty hydrogen bonds. Alternatively, the (H2O)16 cluster is structurally similar to a complicated hydrocarbon generated by undergoing [2+2] cycloaddition of 1,2,3,4,5,6-hexahydropentalene, which reveals the resemblance between water clusters and organic compounds.

Two mixed-ligand Ag(I) coordination polymers (CPs), [Ag2(bpp)2(suc)·12H2O]n (1) and [Ag2(bpe)2(suc)·9H2O]n (2) (where bpp = 1,3-bis(4-pyridyl)propane, bpe = 1,3-bis(4-pyridyl)ethane, and H2suc = succinic acid), have been synthesized and structurally characterized. Both structures consist of cationic layers with Ag···π interacted chains of alternating metal and bis(pyridyl) ligands. The noncoordinated succinate (suc2−) in 1 or 2 serves as an anionic template driving surrounding water molecules to aggregate into an ordered 2D water-suc anionic layer. The interlamellar anions and cationic layers are stacked through weak electrostatic interaction and hydrogen bonds. One novel 1D water chain constructed from alternating water tetramer with uudd configuration and rare octamer exists in the anionic layer of 1. Each octameric water cluster consists of a pair of fused hexameric water clusters, and each water hexamer assumes a rare bag-shaped conformation. A discrete spirocyclic nonameric water cluster featuring two vertex-sharing pentamers, which shows a similar structure to organic hydrocarbon spiro[4.4] nonane, was observed in 2. All water clusters have not been structurally documented so far and illustrate new modes of supramolecular association of water molecules. What is more important is that the present observations demonstrate that the spacer length of N-donor ligands has a significant influence on the final formation of water aggregates.

A unique zero-dimensional (0D) discrete (H2O)14 cluster containing a rare hanging-ladder-like water octamer and an infinite one-dimensional (1D) loose-string-like water chain, respectively, was observed in the coordination polymeric solids {[Cu(bpp)2(H2O)2](tp)·7H2O} (1) and {[Cu(bpp)2(H2O)](ip)·7H2O} (2) (bpp = 1,3-bis(4-pyridyl)propane, tp = terephthalate, and ip = isophthalate), obtained by similar solution phase ultrasonic synthesis techniques, in which 1 (C34H50CuN4O13) crystallized in the monoclinic P21/n space group, Z = 4 (a = 12.824(3) Å, b = 16.867(3) Å, c = 17.660(4) Å; β = 94.50(3)°; V = 3808(1) Å3) and 2 (C34H48CuN4O12) was attributed to the monoclinic P21 chiral space group, Z = 2 (a = 10.439(2) Å, b = 16.863(3) Å, c = 11.302(2) Å; β = 107.84(3)°; V = 1893.9(6) Å3), respectively. Of particular interest, the shapes of water clusters have been obviously well-tuned by modulating different relative orientations of carboxylate groups based on the tp2− and ip2− dianions, demonstrating that water aggregates with different morphologies can be controlled by employing adequate organic anionic species as templates. Both complexes are apparently reducible/oxidizable, which has been confirmed through the electrochemical investigation, and 1 exhibits appreciable electrocatalytic activity for the reduction reaction of nitrite.

The ultrasonic reaction of Ag2O, bipy and H2aze gave rise to a novel Ag(I) mixed-ligand coordination polymer, namely [Ag(aze)(bipy)]·(H2O)3 (1) (bipy = 4,4′-bipyridine, H2aze = azelaic acid). In 1, Ag(I) ions are linked by bipy and aze ligands to form a single two-dimensional (2D) undulated net with a (6,3) topology, incorporating Ag6(bipy)4(aze)2 windows of 22.58 × 11.06 Å based on Ag⋯Ag distances. A pair of identical 2D single nets are interconnected via π⋯π stacking and unsupported Ag⋯Ag interactions to generate a 2D double-layered net. A discrete water hexamer composed of a new planar tetrameric water ring and two pendent water molecules is perpendicularly located in each hydrophilic cavity of the 2D bilayer and acts as a ‘glue’ to assemble adjacent 2D double-layered nets into a three-dimensional (3D) structure.Highlights► The first silver(I) coordination polymer containing azelate ligand was synthesized and structurally characterized. ► The 2D double-layered net is observed in the coordination polymer. ► A discrete water hexamer is perpendicularly located in each hydrophilic cavity of the 2D bilayer. ► Thermal and IR behaviors of the coordination polymer were also discussed.

The reaction of Cu(OH)2 (in situ synthesized from CuCl2·2H2O and NaOH), bpp and H2ox gave rise to a novel Cu(II) coordination polymer under ultrasonic irradiation at ambient temperature, namely [Cu(bpp)(ox)(H2O)·5H2O]n (1) (bpp = 1,3-bis(4-pyridyl)propane, H2ox = oxalic acid). In the complex 1, Cu(II) cations are bridged by bpp ligands to form a one-dimensional (1D) infinite wave-like polymeric chain. The coordinated ox2− anions and water molecules interact with each other by six different hydrogen-bonding motifs and extend the 1D polymeric chain into a two-dimensional (2D) bilayer pattern. Of further interest, one 1D T4(0)A(0) water tape consisting of alternate cyclic water tetramers resides in the channel structure of 1.

In this study we report about two novel azomethine–BODIPY dyads 1 and 2. The two dyads have been, respectively, synthesized by covalent tethering of tautomeric ortho-hydroxy aromatic azomethine moieties including N-salicylideneaniline (SA) and N-naphthlideneaniline (NA) to a BODIPY fluorophore. Both of the two dyads 1 and 2 show enol-imine (OH) structures dominating in the crystalline state. Dyad 1 in the enol state is the most stable form at room temperature in most media, while enol–keto prototropic tautomerism of the NA moiety in solution is preserved in dyad 2, which can be reversibly converted between enol and keto forms in the environment's polarity. Visible illumination of dyad 2 in the enol state excites selectively the BODIPY fragment and then deactivates radiatively by emitting green light in the form of fluorescence, while the emission intensity of 2 in the keto state is quenched on the basis of the proton-coupled photoinduced electron transfer (PCPET) mechanism. This allows large fluorescence modulation between the two states of dyad 2 and generates a novel tautomerisable fluorescent switch. Theoretical calculations including calculated energies, potential energy surfaces (PESs) and intrinsic reaction coordinate (IRC) analysis further support that the single proton transfer reaction from an enol form to a transition state (TS) and from the TS to a keto form for 2 is easier to occur than that for 1, which accounts for the fluorescence quenching of 2 in methanol. The agreement of the experimental results and theoretical calculations clearly suggests that fluorescent and tautomeric components can be paired within the same molecular skeleton and the proton tautomerization of the latter can be designed to regulate the emission of the former. In addition, preliminary experiments revealed that 1 can be potentially used as a simple on/off fluorescent chemosensor which exhibited higher selectivity for Cu2+ over other common cations.

4-Methoxycarbonylphenyl-substituted BODIPY (boron-dipyrromethene) dye gives, in the solid state, three polymorphs. In spite of the absence of any strong intermolecular interactions in all crystalline forms, the three polymorphs show different photoluminescence properties. This behavior highlights the importance of molecular arrangements of the BODIPY moieties in the crystalline state in perturbing their photophysical properties.

A simple 4-aniline boron-dipyrromethene (BODIPY) dye (1) was developed as a highly sensitive acidic pH fluorescent probe excitable with visible light based on a photoinduced electron transfer (PeT) mechanism. The pH titration indicates that the fluorescence intensity increases more than 500-fold within the pH range of 4.12–1.42 with a pKa value of 3.24 in methanol–water (1:1, v/v) solution, which is valuable for studying strongly acidic conditions. Density functional theory (DFT) calculations reproduce the fluorescence off–on behavior. 1 has also been used as a fluorescent chemosensor for the visual detection of dissolved carbon dioxide (CO2) gas. The underlying mechanism of the sensing process is rationalized. This probe can be recovered by bubbling nitrogen (N2) gas into CO2-treated solutions for over 10 cycles. In addition, two logic gates (OR and INH) have been achieved at the molecular level by changing the initial states of system 1 and chemical inputs.

A series of boron dipyrromethene (BODIPY) dyes (B1–B5) having H atoms at 2,6-positions or heavy-atom I at 2-/2,6-positions, and an ortho- or a para-COOH substituted phenyl moiety at the 8-position on the BODIPY core were synthesized and characterized. These organic dyes were applied for investigating the relationship between the BODIPY structure and the effectiveness of homogeneous and heterogeneous visible-light-driven hydrogen production as well as dye-sensitized solar cells (DSSCs). For the homogeneous photocatalytic hydrogen production systems with a cobaloxime catalyst, the efficiency of hydrogen production could be tuned by substituting with heavy atoms and varying carboxyl group orientations of BODIPYs. As a result, B5 containing two I atoms and an ortho-COOH anchoring group was the most active one (TONs = 197). The activity of hydrogen generation followed the order B5 > B3 > B2 > B1 = B4 = 0. An interesting “ortho-position effect” was observed in the present homogeneous systems, i.e., substitution groups were located at the ortho-position and higher hydrogen production activities were obtained. For the heterogeneous hydrogen production systems with a platinized TiO2 catalyst, the effectiveness of hydrogen evolution was highly influenced by the intersystem crossing efficiency, molar absorptivity and positions of the anchoring group of dyes. Thus, B3 having two core iodine atoms and a para-COOH group with TONs of 70 excelled other BODIPYs and the TONs of hydrogen generation showed the trend of B3 > B5 > B2 > B1 = B4 = 0. The results demonstrate that the present photocatalytic H2 production proceeds with higher efficiency and stability in the homogeneity than in the heterogeneity. In the case of DSSCs, the overall cell performance of BODIPY chromophores was highly dependent on both the absence or the presence of iodine atoms on the BODIPY core and –COOH anchoring positions. The B1–TiO2 system showed the best cell performance, because the most effective surface binding mode is allowed with this structure. This is also in contrast with the case of dye-sensitized solar H2 generation, in which B3 was the most efficient chromophore. The differences between dye-sensitized hydrogen-generating systems and DSSCs may be due to rates of electron transfer and the dye aggregation tendency.

A square-planar nickel(II) dithiolate complex is an active molecular catalyst for both photoreduction of protons from water with a turnover number (>1500) and electroreduction of protons from weakly acidic solutions with remarkable turnover frequencies (5575 s−1 at −1.92 V and 1441 s−1 at −1.61 V vs. SCE). DFT calculations provide in-depth insight into the catalytic cycle of the electrochemical reaction, suggesting that the sulfur atoms play crucial roles in proton exchange and hydrogen formation.

A noble-metal-free molecular dyad was constructed by anchoring a thienyl-expanded BODIPY photosensitizer (PS) to a cobaloxime catalyst, which gives a 2.5-fold increase in the TON, and a 3-fold enhancement in the quantum efficiency as compared to the multicomponent catalytic system for the generation of hydrogen via the reduction of water. The stability of PS was expected to improve by introducing the thienyl moiety into the BODIPY core.