Pyrrole and Pyrimidine Derivatives as Possible Electron Donors for Colored Charge-Transfer Complexes with a Weakly Electrophilic Energetic Material,FOX-7:A Theoretical Study

A number of electron-rich heterocycles are studied as potential reagents for visual colorimetric detection of FOX-7 due to colored charge-transfer complexes formation.The obtained results suggest that pyrrole and pyrimidine derivatives can form such complexes playing the role of electron donors despite a low electrophilicity of FOX-7.Density functional theory calculations,as well as quantum theory of atoms in molecules analysis,suggest stacking binding mode as the most preferable one with the binding energy of about 21-36 kJ/mol.All the complexes demonstrate a clear single charge-transfer absorption band in the visible region and the expected colors of the complexes are varying from violet and blue to red and orange.The calculations of the crystalline state of the studied complexes indicate high lattice energies,which are higher than that of pure FOX-7 and are close to the recently reported hydrogen-bonded complex of FOX-7 with 1,10-phenanthroline.Additional analysis of the studied charge-transfer complexes using properties based on density difference grids clearly suggests the acceptor role of FOX-7 in the complexes.This analysis can be effectively applied to identify the nature of other possible complexes of FOX-7,in which its role is unclear because of the specific reactivity,namely,both weak electrophilic and nucleophilic properties at the same time.

Charge-Transfer and SERS Coupling on TiO2

We report the SERS enhancements of Raman forbidden surface modes of TiO2 in different sized TiO2 crystals. This current study utilizes the relationship between the vibronic coupling and the degree of charge-transfer to explain the differences of Surface Enhanced Raman Scattering (SERS) enhancements. Our study shows a direct correlation between the degree of charge-transfer and vibronic coupling. This relationship suggests that charge-transfer between the N-719 dye and TiO2 due to vibronic coupling plays a fundamental role in SERS enhancements. Furthermore, this study shows a strong dependence of the enhancements of the N-719 dye molecular modes to that of the surface modes. This indicates that the mechanism that governs the enhancements of the surface modes in TiO2 crystals most likely also dictates the enhancements of the N-719 dyes.

Sensitive Spectrofluorimetric Method for Determination of Fluoroquinolones through Charge-Transfer Complex Formation

A sensitive spectrofluorimetric method was developed for determination of ciprofloxacin (CPFX), levofloxacin (LEV), gatifloxacin (GAT) and moxifloxacin (MOX) in pure, commercial formulations, human urine and plasma. The method is based on charge-transfer (CT) complex with chloranilic acid. Fluorescence intensity of the complexes was measured at emission wavelength ranging from 445-492 nm with excitation wavelengths from 285-330 nm. At optimum experimental conditions, a linear calibration plot was obtained in the concentration range of 20-1000 ng·mL-1, 60-320 ng·mL-1, 20-800 ng·mL-1 and 20 -00 ng·mL-1 for CPFX, LEV, MOX and GAT, respectively with good correlation coefficient in the range of 0.9929-1.0 in methanolic medium. The limit of detection and limit of quantification were found to be 5 ng·mL-1 and 18 ng·mL-1 for CPFX, 12 ng·mL-1 and 40 ng·mL-1 for LEV, 8 ng·mL-1 and 19 ng·mL-1 for MOX, 6 ng·mL-1 and 19 ng·mL-1 for GAT, respectively. The method was found free of interferences from excipients used as additive in pharmaceutical preparations, some common cations and compounds present in urine and plasma as well as co-administered analgesic, vitamins and other drugs. The method was successfully applied for quantification of selected fluoroquinolones in commercial formulations and also in spiked human urine and plasma samples with percent recoveries of 100.0 ± 1.56 and 100.2 ± 1.29 respectively.

Highly efficient H-bonding charge-transfer complex for microsupercapacitors under extreme conditions of low temperatures

Owing to sluggish ionic mobility at low temperatures, supercapacitors, as well as other energy-storage devices, always suffer from severe capacity decay and even failure under extreme low-temperature circumstances. Solar-thermal-enabled self-heating promises an attractive approach to overcome this issue.Here, we report a unique H-bonding charge-transfer complex with a high photothermal conversion efficiency of 79.5% at 405 nm based on chloranilic acid and albendazole. Integrated with a microsupercapacitor, the chloranilic acid-albendazole complex(CAC) film prompts an apparent temperature increase of 22.7 °C under 1 sun illumination at-32.6 °C, effectively elevating the working temperature of devices.As a result, the rate capability of the microsupercapacitor has been significantly improved with a 17-fold increase in capacitance at a current density of 60 μA cm^(-2), leading to outstanding low-temperature performances. Importantly, the integrated device is capable of working at a low temperature of-30 °C in the open air, which demonstrates the potential of CAC in practical applications for low-temperature ultracapacitive energy-storage devices.

Anisotropic electrical conductivity, phase transition and thermal hysteresis of a charge-transfer salt dibutylammonium bis-7,7,8,8-tetracyanoquinodimethane DBA(TCNQ)_2

This paper reports that a charge-transfer salt dibutylammonium bis-7,7,8,8-tetraeyanoquinodimethane [DBA （TCNQ）2] has been prepared. The temperature dependences of the DC electrical conductivity of the DBA （TCNQ）2 single crystal measured along the crystallographic a, b, and c axes are reported. The crystal shows semicondueting behaviour and the room-temperature conductivities are highly anisotropic （σa = 3.63× 10^-4S/cm, σb = 2.84× 10^-6S/cm, and （σe = 1.82 × 10^-5S/cm）. Particularly, a sharp semiconductor to semiconductor transition has been observed around 270 K on the resistivity curves measured under cooling and heating. In addition, thermal hysteresis phenomena on conductivity and differential scanning calorimetry curves are also reported.

Charge-transfer interaction of drug quinidine with quinol,picric acid and DDQ: Spectroscopic characterization and biological activity studies towards understanding the drug–receptor mechanism

Investigation of charge-transfer （CT） complexes of drugs has been recognized as an important phenomenon in understanding of the drug-receptor binding mechanism. Structural, thermal, morpholo-gical and biological behavior of CT complexes formed between drug quinidine （Qui） as a donor and quinol （QL）, picric acid （PA） or dichlorodicyanobenzoquinone （DDQ） as acceptors were reported. The newly synthesized CT complexes have been spectroscopically characterized via elemental analysis;infrared （IR）, Raman, 1H NMR and electronic absorption spectroscopy; powder X-ray diffraction （PXRD）;thermogravimetric （TG） analysis and scanning electron microscopy （SEM）. It was found that the obtained complexes are nanoscale, semi-crystalline particles, thermally stable and spontaneous. The molecular composition of the obtained complexes was determined using spectrophotometric titration method and was found to be 1：1 ratios （donor：acceptor）. Finally, the biological activities of the obtained CT complexes were tested for their antibacterial activities. The results obtained herein are satisfactory for estimation of drug Qui in the pharmaceutical form

SPECTROPHOTOMETRIC STUDY OF DDQ CHARGE-TRANSFER COMPLEXES WITH 1,10-PHENANTHROLINE AND ITS DERIVATIVES

1,10-phenanthroline and its derivatives can form charge-transfer complexes with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone(DDQ).The absorption spectra and conditions of complex formation,such as the reaction time,the quantity of DDQ, and the solvents, have been studied.After the HMO calculation of phenanthrolines,the molar absorptivities were found to depend on the substituents on the phenanthroline rings.

REACTIVITY RATIOS FOR COPOLYMERIZATION WITH THE PARTICIPATION OF A CHARGE-TRANSFER COMPLEX

The complexation between styrene (St) and N-phenylmaleimide (PMI) was investigated by H-1-NMR spectroscopy, and the existence of a complex was proved. The equilibrium constant of St/PMI in chloroform at 50 degrees C was determined to be 0.27. New elementary propagation reactions were proposed. On the basis of the propagation elementary reactions for copolymerization with the participation of a charge-transfer complex (CTC), a method for measuring the reactivity ratios is presented. Four reactivity ratios and relative reactivities of free monomer and CTC were obtained. They are r(12) = 0.034, r(21) = 0.012, r(1C) = 0.0030, r(2C) = 0.0034, and k(1C)/k(12) = 11.34, k(2C)/k(21) = 3.42.

^(19)F NMR Study on the Charge-Transfer Process between Ground-State Acceptor Fluoranil (or Pentafluorophenyl Carboxylate) and Some N-Alkylphenothiazine Donors

The line positions of 19F NMR absorption of fluoranil (TFQ) or pentafluorophenylcarboxylate (PFE-16) in the presence of N-alkylphenothiazine donors have been measured. By comparing the 19F chemical shift in C6D6 of TFQ or PFE-16 in the absence of the donor with thosein the presence of the donor. the difference of these chemical shifts was found to be large. In thepresence of the donor. 19F upheld shifts of TFQ or PFE-16 have been observed. The experimentalresults showed that there is a charge-transfer process between TFQ or PFE-16 and the donor .When TFQ or PFE-16 accepts the charge from the donor. its 19F resonance moves upfield.

CHARGE-TRANSFER AND ENERGY-TRANSFER IN THE PHOTO-INDUCED COPOLYMERIZATION OF 2-VINYLNAPHTHALENE WITH MALEIC ANHYDRIDE

The initiation mechanism of the copolymerization of 2-vinylnaphthalene with maleic anhydride was studied under irradiation of 365 nm. The excited complex was formed from (1) the local excitation of 2-vinylnaphthalene followed by the charge-transfer interaction with maleic anhydride and (2) the excitation of the ground state charge-transfer complex, and then it collapsed to 1,4-tetramethylene biradical for initiation. A1: 1 alternating copolymer was formed in different monomer feeds. Addition of benzophenone could greatly enhance the rate of copolymerization through energy-transfer mechanism.

Study on Alternating LB Films of Charge-Transfer Complex of Octadecyl-TCNQ and Copper Phthalocyanine Derivative

Infrared spectra of alternating LB films of octadecyl-TCNQ/CuPc are studied. Charge-transfer complexes are formed in LB films and conductance increases about three orders than that of pure CuPc LB films.

Preparation and Crystal Structure of a Charge-transfer Complex between an Organic Substrate and Molybdosilicic Acid [(CH_3)_2NH(CH_2)C_6H_5]_4SiMo_(12)O_(40)·2CH_3CN·H_2O

The charge transfer complex N,N-dimethylbenzylamine which is between the molybdosilicic acid and organic substrate has been prepared. Yellow crystals of the title compound ([(CH3)2NH(CH2)C6H5]4SiMo12O402CH3CNH2O) were synthesized from the mixture of water and acetonitrile. The single-crystal X-ray analysis reveals that the crystal crystallizes in triclinic system, space group P1 with a = 13.313(2), b = 14.673(2), c = 19.736(3) ? a = 86.22(1), b = 88.76(1), g = 66.97(1), V = 3540.2(9) 3 and Z = 2. The anion has the Keggin structure. The MoO bond distances range from 1.675(3) to 1.691(3) ?for the terminal oxygen atoms, 1.798(3) to 2.045(3) ?for the bridging ones, and 2.328(3) to 2.361(3) ?for those in the SiO4 tetrahedron. The SiO bond distances fall in the range of 1.623(3)～1.630(3) ?

Organic stoichiometric cocrystals with a subtle balance of charge-transfer degree and molecular stacking towards high-efficiency NIR photothermal conversion

Charge-transfer(CT)stoichiometric cocrystals are promising choice of organic materials for unveiling the structure-property relationship.However,due to the contradiction between large CT degree required for strong NIR absorption and flexible molecular stacking,construction of stoichiomorphism-based cocystals with near-infrared(NIR)photothermal property remains challenging.Herein,the first example of stoichiomorphism-based photothermal cocrystals were accomplished through the adaptive assembly of 3,3,5,5-tetramethylbenzidine(TMB)donor and 1,2,4,5-tetracyanobenzene(TCNB)acceptor.The selective cocrystallization could be controlled by varying the donor-acceptor stoichiometries via a surfactantassisted method,resulting in two cocrystals with 1:1(T1C1)and 1:2(T2C1)stoichiometries.The absorbance intensity of T1C1 at 808 nm was nearly twice that of T2C1,while the photothermal conversion efficiency(PCE)of the former was 60.3%±0.6%,approximately 80%of that for the latter(75.5%±2.6%),which might be caused by the different intermolecular interactions in distinct molecular stacking patterns.Notably,both excellent PCEs of stoichiometric cocrystals were attributed to the nonradiative transition process,including internal conversion and charge dissociation processes,as elucidated by femtosecond transient absorption spectroscopy measurements.Furthermore,T1C1 was used as an NIR heater for preparing agarose-based photothermal hydrogel,showing great potential for light-controlled in-situ gelation.This strategy of balancing the CT degree and molecular packing orientation not only uncovered the relationship between stoichiometric stacking and photothermal property,but also provided an opportunity to develop advanced organic optoelectronic materials.

Photoluminescent nickel(Ⅱ)carbene complexes with ligand-to-ligand charge-transfer excited states

While nickel(II)complexes have been widely used as catalysts for carbon-carbon coupling reactions,the exploration of their photophysical and photochemical properties is still in the infancy.Here,a series of square-planar Ni(II)complexes[(diNHC)NiX2]bearing chelating benzimidazole-based bis(N-heterocyclic carbene)ligands and varying anionic coligands(1,X=Cl;2,X=Br;3,X=I)are synthesized and structurally characterized.In solid state,both 1 and 2 exhibit orange-red photoluminescence under ambient conditions.The photophysical and electrochemical measurements along with density functional theory(DFT)calculations reveal that the low-energy emissions can be attributed to singlet excited states with ligand-to-ligand charge-transfer(LLCT)character.This work suggests that strong-field N-heterocyclic carbene ligands play a crucial role to achieve the luminescence of Ni(II)complexes.

Elemental Doping Boosts Charge-Transfer Excitonic States in Polymeric Photocatalysts for Selective Oxidation Reaction

Energy-transfer-mediated synthetic reactions play vital roles in the production of high-value-added organics,where the longlived exciton harvesting is an essential precondition for the process.However,for semiconductors with strong excitonic effects like conjugated polymers,their predominant Frenkel exciton with a short lifetime in the unified framework gives rise to low efficiency photocatalysis.Herein,we propose the boosting of the charge-transfer exciton with a long-lived state by introducing spatially separated electron and hole regions.By taking polymeric carbon nitride(PCN)as a prototype,we demonstrate that sulfur doping leads to the formation of electron donor and acceptor motifs in the tri-s-triazinebased backbone,which would accommodate long-lived excitonic states with remarkable charge-transfer characteristics.The extraordinary long-lived charge-transfer exciton harvesting endows sulfur-doped PCN with high-efficiency photocatalytic performance in 1O2 generation and selective oxidation of organic sulfides.This work provides a brand new perspective for designing advanced photocatalysts for energy-transfer-mediated sunlight utilization.

pH-sensitive and biodegradable charge-transfer nanocomplex for second near-infrared photoacoustic tumor imaging

The emerging technique of photoacoustic imaging,especially in the near infra-red(NIR)window,permits high resolution,deep-penetration,clinically reliable sensing.However,few contrast agents are available that can specifically respond to intricate biological environments,and which are biodegradable and biocompatible.Herein,we in troduce a new class of pH-sensitive orga nic photoacoustic con trast age nt that operates in the second NIR window(NIR-II,960-1,700 nm),which is derived from the self-assembled charge-transfer nanocomplex(CTN)by 3,3',5,5'-tetramethylbenzidine(TMB)and its dication structure(TMB++).The unique NIR-ll-responsive CTN can specifically respond to pH change in the physiological range and allows noninvasive and sensitive visualization of the tumor acidic microenvironment(e.g.at pH5)in mice with higher signal-to-noise ratio.The CTN is biodegradable under physiological conditions(e.g.pH 7.4),which alleviates the biosafety concern of nan oparticle accumulati on in vivo.These results clearly show the pote ntial of the TMB/TMB++-based CTN as a promisi ng pH-activated and biodegradable molecular probe for specific tumor photoacoustic imaging in the NIR-II region.

External stimuli controlled multiferroic charge-transfer crystals

Multiferroic charge-transfer crystals have drawn significant interest due to their simultaneous dipolar and spin ordering. Numerous theoretical and experimental studies have shown that the molecular stacking between donor and acceptor complexes plays an important role in tuning charge-transfer enabled multifunctionality. Herein, we show that the charge-transfer interactions can be controlled by the segregated stack, consisting of polythiophene donor- and fuUerene acceptor-based all-conjugated block copolymers. Room temperature magnetic field effects, ferroelectricity, and anisotropic magnetism are observed in charge-transfer crystals, which can be further controlled by photoexcitation and charge doping. Furthermore, the charge-transfer segregated stack crystals demonstrate external stimuli controlled polarization and magnetization, which opens up their multifunctional applications for all-organic multiferroics.

Recent progress on intramolecular charge-transfer compounds as photoelectric active materials

This article summarized the recent advance on the structural design and synthetic strategies of intramolec- ular charge-transfer compounds as well as their potential ap- plications in two-photon absorption chromophores, organic photovoltaics and organic light-emitting diodes.

The contribution of photoinduced charge-transfer enhancement to the SERS of uranyl(Ⅵ) in a uranyl-Ag_2O complex

Charge-transfer(CT) is an important enhancement mechanism in the field of surface-enhanced Raman scattering(SERS) that typically increases the Raman intensity of molecules by as much as 10–100 times.Herein, a low-cost Ag_2O aggregates substrate was prepared via a facile chemical precipitation method,and the calculated CT-based enhancement factor of the uranyl ions adsorbed on it reached as high as 10~5, a metal-comparable value. The efficient photoinduced CT process from the valence band of Ag_2O to the LUMO of uranyl ions under appropriate excitation sources resulted in the repulsion of the axial oxygen atoms of the O=U=O bond, which enhanced its polarizability, creating a more intense Raman mode. To the best of our knowledge, this study firstly reports such a strong photoinduced CT enhancement of uranyl ions, with concentrations of 10^(-8) mol L^(-1) or lower being detected using this Ag_2O substrate. Most importantly, this research has shown that the photoinduced CT enhancement also contributes to the SERS of uranyl ions on pure Ag substrates which have often been ascribed to the electromagnetic enhancement in previous studies. In addition, Ag_2O can be used to selectively detect uranyl ions without interference from many other molecules or ions because of the energy matching rule of the photoinduced CT process, which was readily available for uranyl detection in the environmental aqueous solution.

Fullerene/cobalt porphyrin charge-transfer cocrystals： Excellent thermal stability and high mobility

Although organic semiconductors with high mobility and thermal stability are particularly desirable for practical applications, facile methods for their development still remains a big challenge. In this work, a charge-transfer cocrystal based on fullerene （C70）/cobalt porphyrin supramolecular architecture was prepared by a solution-processable co-assembly strategy. This supramolecular architecture showed hole mobility as high as 4.21 cm2·V-1·s-1, and a relatively high mobility of 0.02 cm2·V-1·s-1 even after thermal treatment at 1,000 ℃. Further studies confirmed the occurrence of charge-transfer from 5,10,15,20- tetrakis（4-methoxyphenyl）porphyrinato cobalt（II） （CoTMPP） to Czo and the paramagnetic character within the supramolecular system. These factors were found to be responsible for the aforementioned superior performances. Thus, a novel organic semiconductor has been reported in this work, which can be potentially used for next generation electronic devices. Furthermore, it has been demonstrated that charge-transfer co-crystallization is a powerful strategy for the rational design and construction of a broad class of new multifunctional organic co-crystalline materials.