Intermolecular Charge-transfer Complexes Research Articles

Synthesis and Characterization of Multiple Stimuli-Responsive Fluorescent Polymer Hydrogels Based on Terpyridine and N-Isopropylacrylamide.

A series of stimuli-responsive fluorescent hydrogels were successfully synthesized via micelle radical copolymerization of hydrophilic acrylamide (AM), hydrophobic chromophore terpyridine-based monomer (TPY), and N-isopropylacrylamide (NIPAM). These hydrogels presented blue emissions (423-440 nm) under room temperature, which is caused by the π-π* transition of the conjugated structures. Once the ambient temperature was increased to 55 °C, the fluorescence color changed from blue (430 nm) to pink (575 nm) within 10 min, subsequently to yellow (535 nm), and eventually back to pink. The thermal-responsive properties are attributed to the transition of the TPY units from unimer to dimer aggregation via the intermolecular charge transfer complex at high temperatures. The hydrogels showed pH-responsive properties. The emission peak of the hydrogel exhibited a blue shift of ~54 nm from neuter conditions to acidic conditions, while a 6 nm red shift to an alkaline environment was observed. The hydrogels demonstrated an obvious change in fluorescence intensity and wavelength upon adding different metal ions, which is caused by the coordination between the terpyridine units incorporated on the backbones and the metal ions. As a consequence, the hydrogels presented a sharp quenching fluorescence interaction with Fe2+, Fe3+, Cu2+, Hg2+, Ni2+, and Co2+, while it exhibited an enhanced fluorescence intensity interaction with Sn2+, Cd2+, and Zn2+. The microstructural, mechanical, and rheological properties of these luminescent hydrogels have been systematically investigated.

Synthesis and high-temperature energy storage performances of fluorinated polyimides

In light of the increasingly stringent requirements for the applications of light-weight flexible high-temperature-resistant dielectric materials in the fields of aerospace, electronics, and electric vehicles, the imperative lies in the development of dielectric materials with high discharged energy density, enduring temperature resistance and high reliability. This work introduced side-chain trifluoromethyl (–CF3) groups into high-temperature engineering polymer polyimides and conducted comprehensive studies on the breakdown and energy storage capabilities. The introduction of bulky –CF3 substituents reduces the intermolecular interactions, increases the free volume, and suppresses the high-temperature leakage conductance loss by decreasing the formation of intermolecular charge transfer complexes between polymer chains. As a result, the fluorinated polyimides (PFI) with lower dielectric constant exhibit enhanced breakdown strengths (730 MV m−1 at 25 °C; 630 MV m−1 at 150 °C), leading to a high discharged energy density of 3.6 J cm−3 (∼1.7 times of pristine polyimides), alongside a charge-discharge energy efficiency of ∼80% at 150 °C. These findings underscore the great potential of PFI for applications in the field of high-temperature energy storage.

Solid-State Emissive Pillar[6]arene Derivative Having Alternate Methylene and Nitrogen Bridges.

Macrocyclic arenes show conformational adaptability, which allows host-guest complexations with the size-matched guest molecules. However, their emission properties are often poor in the solid states due to the self-absorption. Herein, we newly synthesized pillar[6]arene derivatives having alternate methylene and nitrogen bridging structures. Solvatochromic study reveals that the nitrogen-embedding into the cyclic structures can strengthen the intramolecular charge transfer (CT) nature compared to that of the linear nitrogen-bridged precursor. Owing to the large Stokes shift in the solid state, one of the nitrogen-embedded pillar[6]arenes shows high absolute photoluminescence quantum yield (ΦPL=0.36). Furthermore, it displays a turn-off sensing ability toward nitrobenzene (NB) vapor; a fluorescence quenching is observed when exposed to the NB vapor. From the structural analysis before and after the exposure of NB vapor, the amorphous nitrogen-embedded pillar[6]arene efficiently co-crystallize with NB and formed non-emissive intermolecular CT complexes with NB.

Leveraging Intermolecular Charge Transfer for High-Speed Optical Wireless Communication.

Intermolecular charge transfer (CT) complexes have emerged as versatile platforms with customizable optical properties that play a pivotal role in achieving tunable photoresponsive materials. In this study, we introduce an innovative approach for enhancing the modulation bandwidth and net data rates in optical wireless communications (OWCs) by manipulating combinations of monomeric molecules within intermolecular CT complexes. Concurrently, we extensively investigate the intermolecular charge transfer mechanism through diverse steady-state and ultrafast time-resolved spectral techniques in the mid-infrared range complemented by theoretical calculations using density functional theory. These intermolecular CT complexes empower precise control over the -3 dB bandwidth and net data rates in OWC applications. The resulting color converters exhibit promising performance, achieving a net data rate of ∼100 Mb/s, outperforming conventional materials commonly used in the manufacture of OWC devices. This research underscores the substantial potential of engineering intermolecular charge transfer complexes as an ongoing progression and commercialization within the OWC. This carries profound implications for future initiatives in high-speed and secure data transmission, paving the way for promising endeavors in this area.

Dopant-Matrix Afterglow Systems: Manipulation of Room-Temperature Phosphorescence/Thermally Activated Delayed Fluorescence Afterglow Mechanism via Mismatch/Match of Intermolecular Charge Transfer between Dopants and Matrices.

Dopant-matrix organic afterglow materials exhibit ease of fabrication and intriguing functions in diverse fields. However, a deep and comprehensive understanding of their photophysical behaviors remains elusive. Here we report manipulation of a room-temperature phosphorescence/thermally activated delayed fluorescence (RTP/TADF) afterglow mechanism via the mismatch/match of intermolecular charge transfer between dopants and matrices. When dispersed in inert crystalline matrices, the luminescent dopants show RTP lifetimes up to 2 s. Interestingly, when suitable organic matrices are selected, the resultant dopant-matrix materials display a TADF-type afterglow under ambient conditions due to the formation of dopant-matrix intermolecular charge transfer complexes. Detailed studies reveal that reverse intersystem crossing from dopants' T1 states to charge transfer complexes' S1 states, which features a moderate kRISC of 101-102 s-1, is responsible for the emergence of a TADF-type organic afterglow in rigid crystalline matrices. Such less reported delicate photophysics reveals a new aspect of the excited state property in dopant-matrix afterglow systems.

Intermolecular charge-transfer complex between solute and ionic liquid: experimental and theoretical studies

Intermolecular charge-transfer complex between solute and ionic liquid: experimental and theoretical studies

Theoretical study of the Meisenheimer and charge-transfer complexes formed upon colorimetric determination of nitroaromatic explosives

In this paper, we present a theoretical study of structure and UV-vis spectra of 11 colored complexes of nucleophiles with nitroaromatic energetic materials. Two different schemes were found to be the most suitable for absorption spectra simulation. In the case of covalently bound Meisenheimer complexes, the time-dependent density functional theory (TD-DFT) approach with the TPSS functional was the most accurate. Meanwhile, for intermolecular charge-transfer complexes, the closest spectral pattern was provided by the time-dependent Hartree-Fock (TD-HF) scheme with modified exchange contribution (40%). It has been found that the binding type is determined predominantly by the steric factors and less by the electronic effects of the nucleophile, which was approved by the quantum theory of atoms in molecules (QTAIM) analysis of the formed bond types and nucleophilicity index calculations. For the charge-transfer complex, an appropriate configuration with the intermolecular separation between the local electrophilic and nucleophilic sites (the C1···N distance) of about 3.1 Å, was revealed using both classical molecular dynamics simulations and geometry optimizations in polar continuum. Absorption energies and intensities of the electronic transitions are generally well-reproduced in all 11 cases and demonstrate a local π–π* excitation in the covalently-bound complexes and pure charge transfer in intermolecular system. The applied computational methods allow reproducing of the sample colors with a high degree of similarity, which may find their application for modeling of new reagents with other expected colorimetric characteristics.

Attempting to Increase the Effectiveness of the Antidepressant Trazodone Hydrochloride Drug Using π-Acceptors.

Major depressive disorder is a prevalent mood illness that is mildly heritable. Cases with the highest familial risk had recurrence and onset at a young age. Trazodone hydrochloride is an antidepressant medicine that affects the chemical messengers in the brain known as neurotransmitters, which include acetylcholine, norepinephrine, dopamine, and serotonin. In the present research, in solid and liquid phases, the 1:1 charge-transfer complexes between trazodone hydrochloride (TZD) and six different π-acceptors were synthesized and investigated using different microscopic techniques. The relation of dative ion pairs [TZD+, A−], where A is the acceptor, was inferred via intermolecular charge-transfer complexes. Additionally, a molecular docking examination was utilized to compare the interactions of protein receptors (serotonin-6BQH) with the TZD alone or in combination with the six distinct acceptor charge-transfer complexes. To refine the docking results acquired from AutoDock Vina and to better examine the molecular mechanisms of receptor-ligand interactions, a 100 ns run of molecular dynamics simulation was used. All the results obtained in this study prove that the 2,6-dichloroquinone-4-chloroimide (DCQ)/TZD complex interacts with serotonin receptors more efficiently than reactant donor TZD only and that [(TZD)(DCQ)]-serotonin has the highest binding energy value of all π-acceptor complexes.

Tunable Multicolor Circularly Polarized Luminescence via Co-assembly of One Chiral Electron Acceptor with Various Donors

Tunable Multicolor Circularly Polarized Luminescence via Co-assembly of One Chiral Electron Acceptor with Various Donors

Intermolecular charge-transfer complexes between chlorothiazide antihypertensive drug against iodine sigma and picric acid pi acceptors: DFT and molecular docking interaction study with Covid-19 protease

The interaction of chlorothiazide (CH) as donor (D) with picric acid (PA) and iodine (I2) as π- and σ-acceptors (A), respectively, gives charge-transfer (CT) complexes as a final products. The reaction of donor and acceptors were studied spectrophotometrically. The complexes are generally of the n-π* and n-σ* types, with the ground state wave function primarily characterized by the non-bonding structure. For the micro determination of chlorothiazide using picric acid and iodine as acceptors, the ideal conditions encouraging the formation of complexes are thoroughly explored. It was discovered that the stoichiometry of the molecular structure is 1:1 (D:A). The equilibrium constant and the molar extinction coefficient were calculated using Benesi-Hildebrand and its modifications. DFT/TD-DFT calculations with B3LYP/LanL2DZ and 6-311G++ level of theory were used to provide comparable theoretical data along with electronic energy gap of HOMO→LUMO. Molecular docking calculations have been performed between CT complexes and Covid-19 protease (6LU7) to study the interaction between them and their inhibitory effect.

Mechanism of Ir(ppy)3 Guest Exciton Formation with the Exciplex-Forming TCTA:TPBI Cohost within a Phosphorescent Organic Light-Emitting Diode Environment

Cohosts based on hole transporting and electron transporting materials often act as exciplexes in the form of intermolecular charge transfer complexes. Indeed, exciplex-forming cohosts have been widely developed as the host materials for efficient phosphorescent organic light-emitting diodes (OLEDs). In host–guest systems of OLEDs, the guest can be excited by two competing mechanisms, namely, excitation energy transfer (EET) and charge transfer (CT). Experimentally, it has been reported that the EET mechanism is dominant and the excitons are primarily formed in the host first and then transferred to the guest in phosphorescent OLEDs based on exciplex-forming cohosts. With this, exciplex-forming cohosts are widely employed for avoiding the formation of trapped charge carriers in the phosphorescent guest. However, theoretical studies are still lacking toward elucidating the relative importance between EET and CT processes in exciting the guest molecules in such systems. Here, we obtain the kinetics of guest excitation processes in a few trimer model systems consisting of an exciplex-forming cohost pair and a phosphorescent guest. We adopt the Förster resonance energy transfer (FRET) rate constants for the electronic transitions between excited states toward solving kinetic master equations. The input parameters for calculating the FRET rate constants are obtained from density functional theory (DFT) and time-dependent DFT. The results show that while the EET mechanism is important, the CT mechanism may still play a significant role in guest excitations. In fact, the relative importance of CT over EET depends strongly on the location of the guest molecule relative to the cohost pair. This is understandable as both the coupling for EET and the interaction energy for CT are strongly influenced by the geometric constraints. Understanding the energy transfer pathways from the exciplex state of cohost to the emissive state of guest may provide insights for improving exciplex-forming materials adopted in OLEDs.

Highly Efficient and Long‐Range Charge‐Transfer Complex Emission Between Two Blue Phosphorescent Emitters for White Organic Light‐Emitting Diodes

AbstractHerein, the authors report on charge‐transfer (CT) complex emission‐based organic light‐emitting diodes (OLEDs), which emit light by electric field‐induced intermolecular CT complex formation in the light‐emitting layer. Two phosphorescent materials are chosen to have energy level offset for the CT complex formation. This process generates the CT complex, which efficiently emits only in the electroluminescent device by electric‐field‐induced complex formation. A phenylpyridine‐ligand‐based Ir compound and phenylimidazole‐based Ir compounds are selected as the CT complex‐forming materials, and the CT complex exhibits yellow emission under an electric field. Moreover, the doping of the two compounds in the host material produces white OLEDs, exhibiting both blue emission and yellow emission at a quantum efficiency of 13.7%. In particular, the color of the CT complex device can be tuned by the content of each material in the emitting layer. As an initial result, the quantum efficiency is acceptable, and further material development would enhance the quantum efficiency of the CT complex OLEDs. This light‐emitting device can be used in various applications, e.g., a mono‐color or a white‐color light‐emitting diode.

Characterization of intrinsic low-polyimide films studied by positron annihilation

Four kinds of polyimide (PI) films were prepared by polycondensation reaction using the pyromellitic dianhydride (PMDA) and 4, 4′-(Hexafluoroisopropylidene) diphthalic anhydride (6FDA）as the dianhydride monomer, the p-phenylenediamine (PDA), 4-4′-diaminodiphenyl ether (ODA) and 4,4′-(Hexafluoroisopropylidene) bis(p-phenyleneoxy) dianiline (HFBDA) as the diamine monomer respectively. The incorporation of trifluoromethyl groups can effectively inhibit the formation of intermolecular and intramolecular charge-transfer complex (CTC), improve the energy gap and increase the free volume in PI, which leads to an improvement in the optical and dielectric properties in different degree for three fluorinated PI films compared with the Kapton film. The maximum transmittance in visible region reaches 90.5% and the dielectric constant at 104Hz is close to 2.0 for PI6FDA-HFPBDA film. The breakdown strength weakens because of the increase of free volume. The correlation between the dielectric and breakdown characteristics and their free volume has been explained with the help of positron lifetime spectra.

The Impact of Interfacial Interactions on Structural, Electronic, and Sensing Properties of Poly(3‐methylthiophene) in Core‐Shell Nanocomposites. Application for Chemical Warfare Agent Simulants Detection

AbstractIn this paper, structural, electronic, and sensing properties of the poly(3‐methylthiophene) (P3MT) in two types of its core–shell nanocomposites with multiwall carbon nanotubes (MWCNTs) and poly(vinylidene fluoride) with different contents of the P3MT component (shell) are explored and are compared. The results indicate specific changes in the P3MT properties appear due to its interfacial interactions with the MWCNTs and PVDF components. In the case of the doped P3MT, charge transfer from MWCNT to P3MT leads to partial dedoping of the latter. The evidence of intermolecular charge transfer complex formation between undoped P3MT (donor) and MWCNTs (acceptor) is obtained. Changes in the properties of P3MT in nanocomposites are used to detect and to reliably recognize some chemical warfare agent's simulants of nerve agents and mustard gas. The sensitivity dependences of the nanocomposites on their work functions, Hansen solubility parameters and analytes electronegativity are studied. It is shown that the sensor response is controlled by a partial charge transfer if the difference between the work function of the sensing material and the electronegativity of the analyte molecules does not exceed a certain value (in the case herein ≈0.3 eV).

Structural engineering on copolyimide membranes for improved gas separation performance

The structural engineering and design of 6FDA/BPDA-based copolyimide membranes at a molecular level are developed to achieve advanced membrane materials with improved CO2 plasticization resistance as well as high gas separation performance. The commercially available diamine monomers with/without various electronegative groups (-CH3, –CF3 and -Cl) have been employed to prepare 6FDA/BPDA-based copolyimides via the one-step method. All of the copolyimides show excellent solubility in the common solvent, film-forming ability and thus mechanical properties. More interestingly, the intermolecular charge transfer complex (CTC) effects is finely tuned as confirmed by the fluorescence emission spectrum. The introducing of polar chloride groups in the copolyimides could significantly strengthen the CTC effects to prevent the intrusion of condensable CO2 and limit polymeric chain movements. Thus, the membrane based on the 2,2′,5,5′-tetrachlorobenzidine (e.g. 6FDA:BPDA-TSN:TCDB (1:1:1:1)) shows the best carbon dioxide (CO2) plasticization resistance and slowest physical aging without sacrificing gas separation performance versus the membrane having weak polar groups. The CO2 plasticization pressure as high as 350 psi has been observed for the 6FDA:BPDA-TSN:TCDB membrane with polar chloride groups. This value is much higher than that of the copolyimide membranes with –CH3 or –CF3 groups ranging from 100 psi to 200 psi. Moreover, this membrane shows a good gas separation performance, e.g. CO2 permeability of 45.7 barrer and CO2/CH4 ideal selectivity of 35.2 surpassing the commercial cellulose acetate and Matrimid. Such structurally defined polymer with good mechanical strength, plasticization resistance and solubility harnesses the full potential of promising gas separation membrane materials for hollow fiber spinning. This work offers structural engineering guidance for the preparation of high-performance polymers with good tolerance to CO2-induced plasticization.

In Situ Spectrophotometric Investigation of Charge Transfer Complexes Between Triamterene, a Management of Hypertension Drug, and Four Kinds of Nitro Acceptors in Different Organic Solvents

A UV–Vis spectrophotometric method was used to confirm the intermolecular charge-transfer complexes of the drug triamterene (TM) donor with four nitro π-acceptors (2,4,6-trinitrophenol (PA), 4-nitrophenol (4-NP), 4-nitroacetophenone (4-NAP) and m-dinirobenzene (m-DNB)) in methanol, ethanol, acetone, acetonitrile, chloroform, dichloromethane, and dichloroethane at 25 °C. The spectra showed chemical shifts upon the addition of TM to solutions of the nitro acceptors in the solvents. The appearance of new bands or hyper- and hypo-chromic effects confirmed the presence of charge-transfer complexes. The spectra of the complexes of TM and nitro π-acceptors show different absorption bands at different wavelengths for different solvents. The molar ratio method showed a result of 1:1 for the TM–PA system and 1:2 for the TM–4-NP, TM–4NAP, and TM–m-DNB charge-transfer complexes. The physical spectroscopic parameters were calculated, including the formation constant (KCT), molar extinction coefficient (eCT), oscillator strengths (f), ionization potential (Ip), resonance energy (RN), and Gibbs energy (ΔG°). The optical band gap of the TM-nitro charge-transfer complexes was estimated, and there was clearly a relationship between the different kinds of acceptors and their optical band gaps.

A novel approach towards crown-ether modified polyimides with affinity for alkali metal ions recognition

In the attempt to enlarge the family of imide-based materials suitable for sensor applications, novel five- and six-membered thermostable polyimides functionalized with benzo-15-crown-5 ether side chains were synthesized and thoroughly investigated with regard to their affinity for alkali metal ions recognition. For this purpose, a new diamine monomer containing as receptor triphenylmethane modified with 15-crown-5 ether (called by us crowned TPM) has been synthesized and structurally characterized. For the first time, we brought evidence for the occurrence of a ground-state intermolecular charge transfer (CT) complex between the donor crowned TPM diamine and the acceptor diimide segment which is actually responsible for the polyimides strong light emission in the green to yellow spectral range. All polyimides were electrochemically active in both anodic and cathodic regions, their voltammetric response being consistent with the coplanarity and electron accepting strength of the diimide segment. In the presence of alkali metal ions some changes appeared in the electronic absorption signals, although quite diffuse. Instead, these cations significantly altered the fluorescence response of polyimides in dependence on the excitation wavelength, cation type and polymer structure. These mostly caused the occurrence of a new emission band, when the green or yellow fluorescence turned in blue, thus proving the capability of our polyimides to detect alkali metal ions.

Clarifying the effect of moisture absorption and high-temperature thermal aging on structure and properties of polyimide film at molecular dynamic level

A series of pyromellitic dianhydride (PMDA)/4,4′-oxydianiline (ODA) polyimide (PI) films with different moisture content were experimentally prepared and corresponding PI/H2O composite models were constructed and analyzed based on molecular dynamic (MD) simulation. The elongation at break increased from 47.2% to 59.7% when the moisture content of the PI film reached 2%, which was attributed to the presence of water molecules that increased the mobility of molecular chains. The fractional free volume and XRD patterns of the composite models illustrated that the average packing distance of PI chains increased with moisture absorption and weakened intermolecular charge-transfer complex formation, therefore endowing the wet PI films better transmittance. The thermal decomposition mechanism of PMDA/ODA, 3,3′,4,4′-biphenyldianhydride (BPDA)/ODA and BPDA/p-phenylene diamine (PDA) based PI films were also investigated by thermogravimetric-infrared radiation (TG-IR) and MD simulation. The IR spectra of gas products indicated that the thermal decomposition of PI mainly generated CO2, CO, NH3 and HCN, and the PI with different chemical structures had the same thermal decomposition products. The MD results showed that the C–O bond in the ODA structural unit was broken first during the thermal decomposition, which could well explain that the BPDA/PDA exhibited better thermal stability compared with PMDA/ODA and BPDA/ODA. This work paved the way for the investigation of the macromolecular structural evolution of PI materials during moisture absorption and thermal aging process.

Effect of thermal treatment on the structure and gas transport properties of a triptycene-based polybenzoxazole exhibiting configurational free volume

The effect of thermal treatment at 220 °C for 10 days on the structure and transport properties of a triptycene-based polybenzoxazole (TPBO) was investigated experimentally and theoretically. Gas and water vapor sorption in TPBO is virtually unaffected by thermal treatment, while diffusion and permeability coefficients decrease by just 20%. Remarkably, the CO2/CH4 selectivity exhibit a negligible change. Fluorescence spectroscopy, WAXD and FTIR analysis indicate that, in sharp contrast with typical behavior of glassy polymers, TPBO does not experience accelerated physical aging, and rule out formation of intermolecular charge transfer complexes upon thermal treatment. According with this physical picture, the diffusion coefficient of penetrant molecules sorbed in the Langmuir's mode, DH, does not change after treatment. Small molecule diffusivity and permeability decline is caused by a decrease in polymer chain mobility, which makes more difficult opening gaps to allow penetrant diffusion jumps. According to this picture, the Henry's mode diffusion coefficient, DD, substantially decreases upon thermal treatment. The higher stability exhibited by TPBO relative to other high Tg glassy polymers is ascribed to the presence of configurational free volume, which is not related to the non-equilibrium transient conformation, but to the molecular configuration and, as such, it is not relaxed upon protracted exposure to high temperatures.

A Spectroscopic Study in Solution and Solid States: Synthesis, Spectroscopic and Thermal Studies on Intermolecular Charge-Transfer Complexes Associated with the In Situ Reaction of Triamterene Drug with σ- and π-Electron Acceptors

A Spectroscopic Study in Solution and Solid States: Synthesis, Spectroscopic and Thermal Studies on Intermolecular Charge-Transfer Complexes Associated with the <i>In Situ</i> Reaction of Triamterene Drug with <i>σ</i>- and <i>π</i>-Electron Acceptors