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Let there be light! A dithiolate-bridged [FeFe] complex with structural features of the [FeFe] hydrogenase active site has been photoelectrochemically reduced by a p-type Si photocathode at a potential 500 mV less negative compared with a glassy carbon electrode (see figure). In the presence of HClO₄, hydrogen generation has been achieved at a photovoltage of 600 mV with a (105±5) % Faradaic efficiency.

A novel probe design of a pyrene-disulfide molecular assembly has been proposed and its application for the fluorescence turn-on detection of mercury(II) ions (Hg²⁺) has been demonstrated. By taking advantage of the pyrene-assisted efficient photolysis of disulfide bonds, our proposed sensing system exhibits both high selectivity and sensitivity toward Hg²⁺ detection with a detection limit of 5 nM (1 ppb) (see figure).

A series of platinum(II) acetylide complexes with elaborate long-chain pyridine-2,6-dicarboxamides was synthesized. These metal complexes are capable of immobilizing organic solvents to form luminescent metallogels through a combination of intermolecular hydrogen bonding, aromatic π–π, and van der Waals interactions. Fibrillar morphologies were identified by TEM for these metallogels. Unique photophysical properties associated with the sol-to-gel transition have been disclosed with luminescence enhancement at elevated temperatures, which is in sharp contrast to typical thermotropic organogels or metallogels reported in the literature. Such unusual luminescence enhancement is attributed to the increased degree of freedom at higher temperatures that results in the formation of favorable molecular aggregates in the excited state through enhanced aromatic π–π and metallophilic Pt^II⋅⋅⋅Pt^II interactions. Structurally similar Pt-bp3 is not able to gel any common organic solvents. The inability of Pt-bp3 to form gels illustrates the importance of gelation to the macroscopic photophysical properties; Pt-bp3 does not show emission enhancement at elevated temperatures due to its low tendency to form strong aggregates in the ground state.

Hot stuff! A series of platinum(II) acetylide metallogelators with elaborate long-chain pyridine-2,6-dicarboxamides was synthesized and showed unusual emission enhancement at elevated temperatures upon gel-to-sol transition (see figure) due to the higher molecular degree of freedom, which allows rearrangement of molecular aggregates to reach low-energy excimeric assemblies in the excited state.

Almost pure white-light emission (fluorescence quantum yield=0.70) from a remarkably simple single-component, carboxylic acid appended naphthalenediimide (NDI) derivative has been reported. Aggregation-induced modulation of photophysical properties was attributed to hydrogen-bonding-mediated J-type π stacking among the NDI chromophores.

Halopyridiniums also do the trick: An easily accessible class of highly potent bis(pyridinium)-based multidentate halogen-bond (XB) donors is introduced, which, in addition to their inherent XB acidity, also include a built-in redox option (see scheme). These XB donors function as activating reagents for the carbon–bromine bond in benzhydryl bromide. During the reaction, bromide is oxidized to elemental bromine, which forms the basis of a parallel activation mechanism.

Age of bloodstains: Determining the age of a bloodstain at a crime scene is one of the greatest and oldest challenges in forensic science. The results presented herein, with dog blood as a model, indicate a highly reproducible correlation between the fluorescence lifetime and the age of the bloodstain (see figure). The time-dependent changes in fluorescence lifetime were attributed to the alteration of tryptophan.

Turn on and turn red: The CyIQ dye as an internal DNA label can be combined with itself and thiazole red as intrastrand fluorophore pairs (see figure). Excitonic and energy transfer interactions provide interesting alternatives for fluorescence readouts, which are either fluorescence enhancement or fluorescence color change, respectively.

Radical transformers: The chemical transformation of vinylidenecyclopropanes with diphenyl diselenide in the presence of AIBN and upon heating gives the corresponding bicyclo[3.1.0]hexane derivatives in good yields. These compounds undergo thermal-induced radical 1,4-hydrogen shifts through a ring-opening pathway of allylic cyclopropane to give the corresponding cyclohexene derivatives stereoselectively in good yields at 200 °C (see scheme).

Four linear π-conjugated systems with 1,3-diethyl-1,3,2-benzodiazaborolyl [C₆H₄(NEt)₂B] as a π-donor at one end and dimesitylboryl (BMes₂) as a π-acceptor at the other end were synthesized. These unusual push–pull systems contain phenylene (1,4-C₆H₄; 1), biphenylene (4,4′-(1,1′-C₆H₄)₂; 2), thiophene (2,5-C₄H₂S; 3), and dithiophene (5,5′-(2,2′-C₄H₂S)₂; 4) as π-conjugated bridges and different types of three-coordinate boron moieties serving as both π-donor and π-acceptor. Molecular structures of 2, 3, and 4 were determined by single-crystal X-ray diffraction. Photophysical studies on these systems reveal blue-green fluorescence in all compounds. The Stokes shifts for 1, 2, and 3 are notably large at 7820–9760 cm⁻¹ in THF and 5430–6210 cm⁻¹ in cyclohexane, whereas the Stokes shift for 4 is significantly smaller at 5510 cm⁻¹ in THF and 2450 cm⁻¹ in cyclohexane. Calculations on model systems 1′–4′ show the HOMO to be mainly diazaborolyl in character and the LUMO to be dominated by the empty p orbital at the boron atom of the BMes₂ group. However, there are considerable dithiophene bridge contributions to both orbitals in 4′. From the experimental data and MO calculations, the π-electron-donating strength of the 1,3-diethyl-1,3,2-benzodiazaborolyl group was found to lie between that of methoxy and dimethylamino groups. TD-DFT calculations on 1′–4′, using B3LYP and CAM-B3LYP functionals, provide insight into the absorption and emission processes. B3LYP predicts that both the absorption and emission processes have strong charge-transfer character. CAM-B3LYP which, unlike B3LYP, contains the physics necessary to describe charge-transfer excitations, predicts only a limited amount of charge transfer upon absorption, but somewhat more upon emission. The excited-state (S₁) geometries show the borolyl group to be significantly altered compared to the ground-state (S₀) geometries. This borolyl group reorganization in the excited state is believed to be responsible for the large Stokes shifts in organic systems containing benzodiazaborolyl groups in these and related compounds.

Unusual push–pull systems containing 1,4-phenylene, 4,4′-biphenylene, 2,5-thiophene and 5,5′-dithiophene (shown here) as π-conjugated bridges and different types of three-coordinate boron moieties serving as π-donors (1,3,2-benzodiazaborolyl) and π-acceptors (dimesitylboryl) were prepared. The HOMO in the blue-green fluorescing compounds is mainly diazaborolyl in character; the LUMO is dominated by the empty p orbital at the boron atom of the BMes₂ group.

A series of novel triazole derivative pyridine-based polyamino–polycarboxylate ligands has been synthesized for lanthanide complexation. This versatile platform of chelating agents combines advantageous properties for both magnetic resonance (MR) and optical imaging applications of the corresponding Gd³⁺ and near-infrared luminescent lanthanide complexes. The thermodynamic stability constants of the Ln³⁺ complexes, as assessed by pH potentiometric measurements, are in the range log K_LnL=17–19, with a high selectivity for lanthanides over Ca²⁺, Cu²⁺, and Zn²⁺. The complexes are bishydrated, an important advantage to obtain high relaxivities for the Gd³⁺ chelates. The water exchange of the Gd³⁺ complexes (k_ex²⁹⁸=7.7–9.3×10⁶ s⁻¹) is faster than that of clinically used magnetic resonance imaging (MRI) contrast agents and proceeds through a dissociatively activated mechanism, as evidenced by the positive activation volumes (ΔV^≠=7.2–8.8 cm³ mol⁻¹). The new triazole ligands allow a considerable shift towards lower excitation energies of the luminescent lanthanide complexes as compared to the parent pyridinic complex, which is a significant advantage in the perspective of biological applications. In addition, they provide increased epsilon values resulting in a larger number of emitted photons and better detection sensitivity. The most conjugated system PheTPy, bearing a phenyl–triazole pendant on the pyridine ring, is particularly promising as it displays the lowest excitation and triplet-state energies associated with good quantum yields for both Nd³⁺ and Yb³⁺ complexes. Cellular and in vivo toxicity studies in mice evidenced the non-toxicity and the safe use of such bishydrated complexes in animal experiments. Overall, these pyridinic ligands constitute a highly versatile platform for the simultaneous optimization of both MRI and optical properties of the Gd³⁺ and the luminescent lanthanide complexes, respectively.

Bimodal application: Pyridine-based polyamino–polycarboxylate ligands (see figure) ensure non-toxicity as well as advantageous magnetic and luminescence properties for the corresponding Gd³⁺ and near-infrared-emitting lanthanide complexes.