THF Solution Research Articles

Mono-/multi-fluorination of 1,8-naphthalimides for developing AIE/AIEE fluorophores with tuning emission wavelength

Aggregation-induced emission/aggregation-induced emission enhancement (AIE/AIEE) luminogens provides amount of highly emissive materials in density states for versatile applications. Most of the AIE/AIEEgens were designed with the multiply rotation unit, in which the additional rotation units not only extend the molecular structure but also suffer from low atom economy. Herein, a fluorination strategy was introduced to construct ten AIE/AIEEgens with 1∼3 fluorine (F) atoms at different position of phenyl ring at previous developed AIEgen, 4-phenyl-1,8-naphthalimide, which can output tuning emissive wavelength and high quantum yields in both aqueous solutions and solids. In these compounds, five AIEgens with ortho-F atom and five AIEEgens without ortho-F atom were obtained. All compounds show bright blue emissions centered at 430–485 nm in aqueous solutions and wide emissions covering visible region in solid states. We calculated the ratio of quantum yields between their aqueous solution and THF solution (Φwater/ΦTHF). The AIE luminogens show the higher ratios between 10.19 and 24.89 and the AIEEgens show the lower ratios between 1.89 and 6.40. This strategy based on changing the substituent positions of F atoms provides an efficient and convenient method for construction of novel AIE-active materials with variable photophysical properties in density states.

Half‐Sandwich Iron Chalcogenopropargylcarbonato Complexes as CO‐Releasing Molecules

ABSTRACTInteraction of iron chalcogenides (μ‐Ex)[CpFe(CO)2]2 (E = S; x = 2–4, E = Se, x = 1) with propargyl chloroformate (ClCO2CH2C≡CH) in diethyl ether yielded iron(II) chalcogenopropargylcarbonato complexes CpFe(CO)2ECO2CH2C≡CH (E = S (1), Se (2)). These complexes have been characterized by elemental analysis, UV–Vis, IR, and 1H‐ and 13C{1H}‐NMR spectroscopy and single‐crystal x‐ray diffraction techniques. Further, the suitability of complexes 1 and 2 as CO‐releasing molecules (CORMs) for the administration of carbon monoxide has been studied. CO gas is released upon irradiation of THF solution of these complexes in the presence of hemoglobin.

A novel fluorescent probe based on coumarin derivatives-grafted cellulose for specific detection of Fe3+ and its application

Fe3+ is one of the most important ions for maintaining the normal growth of plants and animals. However, imbalance and accumulation of Fe3+ can lead to serious damage to the environmental system. Hence, it is considerably crucial to monitor the concentration of Fe3+. In this paper, a high-performance fluorescent probe CA-NCC for specifically detecting Fe3+ was obtained by grafting cellulose acetate (CA) with coumarin derivative (NCC). The resulted probe displayed a bright blue fluorescence in THF solution and showed a distinct “turn-off” fluorescence response to Fe3+, while the small molecule compound NCC could not realize the detection of Fe3+. CA-NCC displayed excellent response performance to Fe3+ including excellent selectivity and sensitivity, rapid reaction time (2.5 min), wide pH detection range (6–11), and low detection limit (0.178 µM). More importantly, CA-NCC was successfully fabricated into fluorescent film based on the good processability of cellulose acetate, and achieved highly selective recognition of Fe3+ from various metal ions.

Effect of multi-donor and extended π-conjugation in ferrocene appended indanedione chromophores for aggregation induced emission enhancement (AIEE) and nonlinear optics†

A new (D-D’π-A) type ferrocene and methoxyphenyl (D-D′) conjugated indanedione (A) based linear and π-extended multi-donor-π-acceptor chromophores 1–4 were synthesized and characterized. The chromophores 2–4 were further investigated by single-crystal analysis through X-ray diffraction, revealing centrosymmetric space groups with non-covalent interactions (inter, intramolecular hydrogen bonding, and C–H…π interactions) and these molecular packing interactions favor SHG efficiencies. Electrochemical studies show the one-electron charge transfer (Fe2+⇌Fe3+) and observed greater redox potential of chromophore 4 than the parent ferrocene due to the substitution effect. The solvatochromic studies in emission spectra resulted in redshift (56–109 nm) for the chromophores 1–4 by increasing the solvent polarities, which indicates higher excited state stabilization relative to the ground state, results effective intramolecular charge transfer process within the chromophores. The occurrence of ferrocene moieties lowers the fluorescence intensities of the chromophores 1–4, which was overcome through aggregation induced emission enhancement (AIEE) studies at 60 % (THF/H2O). The AIEE state also shows 23 times higher quantum yield than the THF solution for chromophore 4. In addition, a thin film using polymethyl methacrylate as a binder shows a significant blue shift with higher emission intensity than those obtained in the solution due to the intermolecular interactions and enhancement of viscosity. The SHG efficiency studied using the Kurtz and Perry powder technique results in a higher value for chromophore 4 (2 times higher than the reference KDP) attribute to the multi donors, acceptor, and extended π conjugation reducing the anti-parallel alignment in the solid state. The computational calculations were done to validate the experimental results using B3LYP/6-31+G** level of theory.

Bio-Based Polyurethane-Urea with Self-Healing and Closed-Loop Recyclability Synthesized from Renewable Carbon Dioxide and Vanillin.

Developing recyclable and self-healing non-isocyanate polyurethane (NIPU) from renewable resources to replace traditional petroleum-based polyurethane (PU) is crucial for advancing green chemistry and sustainable development. Herein, a series of innovative cross-linked Poly(hydroxyurethane-urea)s (PHUUs) were prepared using renewable carbon dioxide (CO2) and vanillin, which displayed excellent thermal stability properties and solvent resistance. These PHUUs were constructed through the introduction of reversible hydrogen and imine bonds into cross-linked polymer networks, resulting in the cross-linked PHUUs exhibiting thermoplastic-like reprocessability, self healing, and closed-loop recyclability. Notably, the results indicated that the VL-TTD*-50 with remarkable hot-pressed remolding efficiency (nearly 98.0%) and self-healing efficiency (exceeding 95.0%) of tensile strength at 60 °C. Furthermore, they can be degraded in the 1M HCl and THF (v:v = 2:8) solution at room temperature, followed by regeneration without altering their original chemical structure and mechanical properties. This study presents a novel strategy for preparing cross-linked PHUUs with self-healing and closed-loop recyclability from renewable resources as sustainable alternatives for traditional petroleum-based PUs.

One- and Two-Photon Photophysical Properties, Ultrafast Dynamics, and DFT Study of Three Modified Zinc Phthalocyanines.

As two-photon absorption (TPA) materials, phthalocyanine molecules have promising application prospects due to their large TPA absorption cross-section, high third-order nonlinear optical susceptibility, and ultrafast response characteristics. In this work, optical properties and the ultrafast response of three modified zinc phthalocyanine molecules (P-HPcZn, Pc-P-Pc, and (DR1)4PcZn) were analyzed. No obvious side-shoulder absorption peaks in the Q-band can be observed from the steady-state absorption spectra of the three molecules, confirming the lack of aggregation products in the solutions of our measurement. Open-aperture Z-scan results show relatively large TPA cross-section values of 136.4 and 55.3 GM for Pc-P-Pc and (DR1)4PcZn, respectively. The nonlinear optical results show that the absorption process observed under the excitation of femtosecond pulses is a reverse saturable absorption (RSA) mechanism. Up-conversion fluorescence spectra of (DR1)4PcZn in THF solution indicate that the fluorescence emission mechanism is TPA. In the study of ultrafast dynamics, the transient absorption spectra were investigated and the decay lifetime of the dynamic traces corresponding to some representative probe wavelengths was obtained through data fitting with a multi-exponential function. Finally, the charge transfer and excited state properties of the modified zinc phthalocyanine molecules were discussed in depth by the DFT method. The energy gaps of P-HPcZn, Pc-P-Pc, and (DR1)4PcZn are 2.16, 1.39, and 2.13 eV, respectively. The results indicate that the Pc-P-Pc of donor-acceptor-donor (D-A-D) structure has the smallest energy gap as well as the best charge transfer properties.

Hydrogen Atom Abstraction and Reduction Study of 21-Thiaporphyrin and 21,23-Dithiaporphyrin.

The metal-free porphyrins protonation has gained interest over five decades because its structure modification and hardly monoacid intermediate isolation. Here, upon the hydrogen atom abstraction processes, one step diproptonated H3STTP(BF4)2 (STTP = 5,10,15,20-tetraphenyl-21-thiaporphyrin) (3) and stepwise protonated HS2TTPSbCl6 (5) and diprotonated H2S2TTP(BF4)2 (6) (S2TTP = 5,10,15,20-tetraphenyl-21,23-thiaporphyrin) compounds were obtained using HSTTP and S2TTP with oxidants. The closed-shell protonated compounds were fully characterized using XRD, UV-vis, IR and NMR spectra. In addition, the reduced 19π compounds [K(2,2,2)]HSTTP (2) and [K(2,2,2)]S2TTP (7) were synthesized by the ligands with reductant KC8 in THF solution. These two open-shell compounds were characterized with UV-vis, IR and EPR spectroscopies. The semiempirical ZINDO/S method was employed to analyze the HOMO/LUMO gap lever and identify the electronic transitions of the UV-vis spectra of the closed- and open-shell porphyrin compounds.

Novel Dual-Emission Emitters Featuring Phenothiazine-S-Oxide and Phenothiazine-S,S-Dioxide Motifs.

In this study, we have successfully designed and synthesized two novel dual-emission emitters featuring phenothiazine-5-oxide and phenothiazine-5,5-dioxide motifs, characterized by highly lopsided and asymmetric conformational states. Through rigorous spectral examinations and DFT calculations, the compounds exhibit distinctive ICT phenomena, coupled with efficient emission in solid states and AIEE characteristics under high water fractions in DMF/H2O mixtures. These non-planar luminogens exhibit vibrant green and blue solid-state luminescence, with fluorescence quantum yields of 24.1 % and 15.21 %, respectively. Additionally, they both emit green fluorescence in THF solution, with notable emission quantum yields (QYs) 36.4 % and 30.4 %. Comprehensive theoretical investigations unveil well-defined electron cloud density separation between the energies of HOMO/LUMO levels within the two luminogens. Notably, the targeted molecule harboring the phenothiazine-S,S-dioxide motif also demonstrates remarkable reversible mechanofluorochromic properties. Moreover, we testify their potential in applications such as solid-state rewritable information storage and live-cell imaging in solution states. Through theoretical calculations and comparative studies, we have explored the intrinsic relationship between molecular structure and performance, effectively screening and identifying new fluorescent molecules exhibiting outstanding luminescent attributes. These discoveries establish a robust theoretical and technical foundation for the synthesis and application of efficient DSE-based MFC materials, opening new avenues in the realm of advanced luminescent materials.

Preparation and Properties of Multi-Responsive Liquid Crystalline Poly(urethane-acrylate)s and Its Composite Membranes.

In this work, a kind of side chain liquid crystalline poly(urethane-acrylate)s was synthesized by free polymerization based on self-made liquid crystalline monomers, and a series of liquid crystalline polyurethane/shape memory polyurethane composite membranes were prepared by electrospinning. The synthesized liquid crystalline poly(urethane-acrylate)s have excellent thermal stability. Due to the regular arrangement of azobenzene on the side chains, polymers can rapidly undergo a photoinduced transition from trans-isomerism to cis-isomerism in THF solution and restore reversible configurational changes under visible light. The composite membranes prepared by electrospinning can also undergo photoinduced deformation within 6 s, and the deformation slowly returns under visible light. Meanwhile, the composites have shape memory, and after deformation caused by stretching, the membranes can quickly recover their original shape under thermal stimulation. These results indicate that the composites have triple response performances of photoinduced deformation, photo-, and thermal recovery.

Sensing of Co2+ and Cu2+ Ions Using Dimethylamino-functionalized Poly(azomethine-1,3,4-oxadiazole)s.

The ability of OxT and OxFl azomethines to recognize metal ions in THF solutions was investigated using UV-vis absorption techniques. Various metal ions, including Cd2+, Hg2+, Co2+, Sn2+, Cu2+, Ni2+, Zn2+ and Ag+, were tested. The absorption spectra revealed two distinct π-π* transition bands in the 273-278nm and 330-346nm wavelength ranges. Additionally, OxFl displayed an absorption peak at 309nm, attributed to the fluorene group. Spectral titrations were used to study the fluorescence behavior in the presence of these metal ions. The results showed significant quenching with Co2+ and Cu2+ ions, while other metal ions had minimal effects on the fluorescence intensity. The quenching mechanism was further analyzed using the Stern-Volmer and Lehrer equations, and the binding constants ( ) were calculated using the Benesi-Hildebrand relations. The results confirm that Co2+ has a 1:2 stoichiometry and Cu2+ has a 1:1 stoichiometry, indicating the strong affinity of OxFl and OxT for these ions. The negative values of ΔG (Gibbs free energy) suggest that complex formation occurs spontaneously at room temperature.

Tunable Nano-Bending Structures of Loosened/Tightened Lassos with Bi-Stable Vibration-Induced Emissions for Multi-Manipulations of White-Light Emissions and Sensor Applications.

The first tunable nano-bending structures of [1]rotaxane containing a single-fluorophoric N,N'-diphenyl-dihydrodibenzo[a,c]phenazine (DPAC) moiety (i.e., [1]RA) are developed as a loosened lasso structure to feature the bright white-light emission [CIE (0.27, 0.33), Φ = 21.2%] in THF solution, where bi-stable states of bending and twisted structures of DPAC unit in [1]RA produce cyan and orange emissions at 480 and 600nm, respectively. With acid/base controls, tunable loosened/tightened nano-loops of corresponding [1]rotaxanes (i.e., [1]RA/[1]RB) can be achieved via the shuttling of macrocycles reversibly, and thus to adjust their respective white-light/cyan emissions, where the cyan emission of [1]RB is obtained due to the largest conformational constraint of DPAC moiety in its bending form of [1]RB with a tightened lasso structure. Additionally, the non-interlocked analog M-Boc only shows the orange emission, revealing the twisted form of DPAC fluorophore in M-Boc without any conformational constraint. Moreover, the utilization of solvents (with different viscosities and polarities), temperatures, and water fractions could serve as effective tools to adjust the bi-stable vibration-induced emission (VIE) colors of [1]rotaxanes. Finally, tuning ratiometric emission colors of adaptive conformations of DPAC moieties by altering nano-bending structures in [1]rotaxanes and external stimuli can be further developed as intelligent temperature and viscosity sensor materials.

Tetrakispyrazolylethene: Protonation-Induced Emission.

Tetrakispyrazolylethene (1) was synthesized from pyrazole and hexachloroethane through a one-step substitution reaction. The increase of emission was detected both in solid and aqueous THF solution, compared with that in anhydrous THF. While the former originates from the crystal packing, the latter is attributed to the protonation-induced emission, independent of aggregation, based on the optical measurement under varying concentrations and particle-size distribution analysis.

Novel Bicyclic P,S-Heterocycles via Stereoselective hetero-Diels-Alder Reactions of Thiochalcones with 1-Phenyl-4H-phosphinin-4-one 1-Oxide.

Thiochalcones undergo cycloaddition reactions in THF solution at 60 °C with the synthetically unexplored 1-phenyl-4H-phosphinin-4-one 1-oxide in a highly regio- and stereoselective manner, yielding hitherto unknown bicyclic P,S-heterocycles containing fused thiopyran and phosphinine rings. The stereochemical structures of two of the obtained (4+2)-cycloadducts were unambiguously assigned by means of the X-ray single-crystal analysis. Based on these assignments, a concerted mechanism of the hetero-Diels-Alder reaction via the preferred endo approach of the heterodiene from the less hindered P=O side of the phosphininone molecule is postulated to explain the established rac-(4RS,8SR,9SR,10SR)-configured (4+2)-cycloadducts isolated as major products.

Non-destructive chemical prelithiation of VO2(B) anodes constructing a multifunctional interphase layer for advanced Li-Ion batteries

VO2(B) stands as a promising anode material, comparable to the disordered rock-salt phase Li3+xV2O5, owning to its ease of preparation, suitable redox potential, and remarkable rate capability. However, the practical application of VO2(B) anodes faces substantial limitations due to its low initial coulombic efficiency (ICE) and instability of solid electrolyte interface (SEI) layer during cycling. In this study, we introduce a highly efficient, controllable, and non-destructive chemical prelithiation method utilizing a reductive Li-arene reagent, formed by dissolving Li-metal to THF solutions containing biphenyl derivatives. This method enables the VO2(B) anode to achieve an ICE of nearly 100 %. The investigation on the chemical composition and mechanical properties of SEI layers reveals that the prelithiated VO2(B) electrode contains a more favorable LiF component, fewer adverse byproducts, and exhibits a thinner thickness with high structural strength. Kinetic analysis demonstrates that the prelithiation treatment accelerates the diffusion of lithium ions, reduces interfacial reaction resistances, and maintains interface stability during cycling. To demonstrate the practical application, we assemble a well-designed Prelithiation VO2(B)||NCM811 full cell, achieving an enhancement in the energy density of at least 20 %. This work underscores the potential of prelithiated VO2(B) electrodes for developing lithium-ion batteries (LIBs) with high-safety and high-energy/power density.

Exploring the mechanisms of excited-state intramolecular proton transfer in hydroxyphenyl-benzimidazole derivatives: A theoretical perspective

We conducted a comprehensive theoretical exploration for the ESIPT mechanism in a set of HBI derivatives in THF solution (Cpd-A and Cpd-B, and three isomers: Cpd-1, Cpd-2 and Cpd-3), employing time-dependent density functional theory (TD-DFT) methods for the excited-state calculations. An energy scan for the excited-state proton transfer pathway indicates that both Cpd-A and Cpd-B exhibit a low transition barrier from Enol* to Keto*, with the energy of Keto* much lower than Enol* state, which implies a rapid ESIPT process. The high instability of Enol* state contradicts the experimental observed dual emission bands for Cpd-A, where the emission band predominantly contributed from Keto* state. We propose a new mechanism to account for this dual fluorescence phenomenon of Cpd-A, where the overall fluorescence band can be ascribed to the emissions from both Keto* and a stable rotamer of Cpd-A. Calculations suggest that Cpd-A can exist in both syn and anti rotamers, with a relatively low isomerization barrier of 14.0 kcal/mol. The coexistence of two stable isomers in solution gives rise to the phenomenon of dual emission for Cpd-A. Further investigation for the substituent effects on the ESIPT dynamics of three isomers (Cpd-1, Cpd-2 and Cpd-3) indicates that varying substituent positions can have a substantial impact on both ESIPT process and excited-state charge transfer. The methoxy group substitution proximate to the hydroxy functional group decreases the energy barrier for Enol*-Keto* transition, and also promotes a more substantial charge transfer. Our study demonstrates a new mechanism of the dual fluorescence observed for the target HBI derivatives, offering a novel understanding for the ESIPT mechanism in solvent.

Thermodynamic phase equilibria study of Hythane (methane + hydrogen) gas hydrates for enhanced energy storage applications

Hydrogen blending with natural gas has become an effective technique for incorporating the characteristics of natural gas and facilitating the storage and transportation of hydrogen gas. The transportation of hydrogen and natural gas (methane) blend, also referred to as Hythane, presents numerous challenges, advantages, and disadvantages that differ based on the technology employed. The current research showcased a thorough examination of the thermodynamics involved in studying the three phase equilibrium analysis of gas hydrate technology for storing Hythane gas mixtures. Three different Hythane compositions varying in hydrogen percentage were selected, and the isochoric gas hydrate phase equilibria study was performed. The experimental results of phase equilibria and thermodynamic modelling using CPA EOS in software were compared. A similar study was also conducted in the presence of a 5.56 mol % THF solution to understand the reduction in the pressure requirement for the phase equilibria. Results from the mixed Hythane+THF gas hydrate findings suggested stable gas hydrate formation at much lower pressure requirements, increasing the credibility of storing Hythane mixtures in gas hydrates at moderate conditions. The gas compositions for each experiment were analyzed using gas chromatography to evaluate the presence of the desired gas in the hydrate phase. Heat exchange during the gas hydrate dissociation was analyzed using a high pressure differential scanning calorimeter (DSC). The change in the heat release temperature also indicates the stability of the gas hydrate, and with increasing hydrogen gas in the blend, the gas hydrate stability decreased. The Clausius-Clapeyron equation was employed to compute the heat of gas hydrate dissociation, and a comparison was made with the heat of dissociation obtained from the DSC study. The experimental investigations on Hythane gas hydrates were performed to find the hydrogen storage inside the gas hydrate phase and compare it with the previous studies of pure hydrogen hydrates. To demonstrate the Hythane gas transportation, Hythane gas hydrate pellets were formed, followed by their storage in a controlled environment to observeany changes in pressure and temperature. The Hythane gas hydrate pellets demonstrated exceptional stability of Hythane gas presenting an intriguing prospect for utilizing gas hydrate technology in Hythane gas transportation.

Stimuli-Responsive Properties of a Zinc(II) Salen-Type Schiff-Base Complex and Vapochromic Detection of Volatile Organic Compounds.

This contribution reports, through a combined thermogravimetric analysis, differential scanning calorimetry, UV-vis, powder X-ray diffraction, and Rietveld refinement analysis, on the stimuli-responsive chromic properties of a substituted Zn(salmal) Schiff-base Lewis acidic complex with unique and distinct thermo- and vapochromic characteristics. The solid complex obtained in air or by evaporation of the solvent from their THF solutions shows a marked thermochromism associated with a phase transition, unusually triggered by the reversible desorption/adsorption of one lattice water molecule. In contrast, the anhydrous solid, achieved from THF solutions of the complex by evaporation of the solvent under anhydrous conditions, behaves very differently as it does not show any absorption of water or thermochromism and exhibits varied vapochromic properties. Detection of volatile organic compounds having Lewis basicity is demonstrated by using the anhydrous solid or the related cast films on glass or paper substrates. In both cases, a marked vapochromism is observed upon exposure to vapors of various volatile species and involves well-defined optical absorptions and naked-eye color changes, also allowing the discrimination of primary aliphatic amines. Vapochromic behavior with the formation of stable, stoichiometric adducts is also demonstrated for both the solid obtained in air and the anhydrous solid or for the related cast films after exposure to vapors of pyridine.

Microstructural investigation of the cooperative gelation of syndiotactic polystyrene and high MW polyethylene glycol di-methyl ether in common solution in THF

The gelation of syndiotactic polystyrene (sPS) in THF in the presence of high molecular weight PEGDME was investigated in detail using contrast-matching SANS complemented by in situ FTIR. Using the contrast-matching method, the scattering contribution of each of the two polymers in the common solution in THF at high temperature (110 °C), in the single-coil conformational state and in the gelation state of sPS (below 40 °C and down to 10 °C) was observed, and the structural characterization of the polymer coils and the junction structures of the gel was obtained. The local scale conformation of the two types of polymer molecules in the different regimes was additionally monitored by FTIR. The gelation and melting temperatures were determined by DSC. sPS changes from the amorphous coil to the helical TTGG conformation when the gelation temperature is passed, forming fibrillar morphologies with a local 2D aspect due to cooperative interactions with the solvent molecules. These are the junction structures of the large-scale network morphology of the gel. The high molecular weight PEGDME transitions from the amorphous coil to an elongated amorphous conformation and incorporates into the fibrillar morphology together with the sPS during the gelation process. High MW PEGDME alone in THF forms a "house of cards" gel consisting of stacked lamellar structures on a smaller length scale, as shown by the scattering data. Thus, in the presence of sPS, smaller and softer structures appear as a result of a cooperative gelation process controlled by sPS. Incorporation of high MW PEGDME into these aggregates leads to polymer nanocomposites that can render the sPS hydrophilic, a topic that should be the focus of future structural and morphological studies.

Phenylbenzothiazole-Based Platinum(II) and Diplatinum(II) and (III) Complexes with Pyrazolate Groups: Optical Properties and Photocatalysis.

Based on 2-phenylbenzothiazole (pbt) and 2-(4-dimethylaminophenyl)benzothiazole (Me2N-pbt), mononuclear [Pt(pbt)(R'2-pzH)2]PF6 (R'2-pzH = pzH 1a, 3,5-Me2pzH 1b, 3,5-iPr2pzH 1c) and diplatinum (PtII-PtII) [Pt(pbt)(μ-R'2pz)]2 (R'2-pz = pz 2a, 3,5-Me2pz 2b, 3,5-iPr2pz 2c) and [Pt(Me2N-pbt)(μ-pz)]2 (3a) complexes have been prepared. In the presence of sunlight, 2a and 3a evolve, in CHCl3 solution, to form the PtIII-PtIII complexes [Pt(R-pbt)(μ-pz)Cl]2 (R = H 4a, NMe2 5a). Experimental and computational studies reveal the negligible influence of the pyrazole or pyrazolate ligands on the optical properties of 1a-c and 2a,b, which exhibit a typical 3IL/3MLCT emission, whereas in 2c the emission has some 3MMLCT contribution. 3a displays unusual dual, fluorescence (1ILCT or 1MLCT/1LC), and phosphorescence (3ILCT) emissions depending on the excitation wavelength. The phosphorescence is lost in aerated solutions due to sensitization of 3O2 and formation of 1O2, whose determined quantum yield is also wavelength dependent. The phosphorescence can be reversibly photoinduced (365 nm, ∼ 15 min) in oxygenated THF and DMSO solutions. In 4a and 5a, the lowest electronic transitions (S1-S3) have mixed characters (LMMCT/LXCT/L'XCT 4a and LMMCT/LXCT/ILCT 5a) and they are weakly emissive in rigid media. The 1O2 generation property of complex 3a is successfully used for the photooxidation of p-bromothioanisol showing its potential application toward photocatalysis.

Two Allogons of an O2 -activating Bis(disiloxido)ferrate(II) Accessible Selectively just by Variation of the Crystallization Temperature.

Deprotonation of O(iPr2 SiOH)2 (iPr LH2 ) with LiOtBu followed by reaction with FeCl2 in THF led to the complex [iPr L2 Fe][Li(THF)2 ]2 , 2, which represents a structural and spectroscopic model of the α-Fe sites of Fe/ZSM-5. Reaction with O2 in THF solution proceeds rather fast and is complete within 200 ms; an intermediate O2 adduct could not be identified by stopped-flow methods. Cooling blue solutions of 2 to -80 °C led to the growth of blue crystals of 2⋅THF, the analysis of which by XRD revealed a FeO4 core that is somewhat distorted from planarity towards a tetrahedral structure. By contrast, cooling such solutions to -30 °C led to pink crystals of an allogon featuring a perfectly square planar FeO4 entity. Hence, 2 represents a unique case where two different structural isomers (allogons) can be crystallized from the same solvent selectively, controlled by the temperature. DFT calculations were performed to understand this finding.