Strong Intermolecular Charge Transfer Research Articles

Design and synthesis of simple quinoline-based organic molecules as dual/multifunctional chemosensors for the detection of Cu2+/Fe3+ ions

The current research deals with the sensitivity of a turn-on-off fluorescence chemosensor using the probe, namely (E)-2-(((2‑hydroxy-5-methylphenyl) imino)methyl) quinolin-8-ol (HQ-AMP) as a selective detection of Cu2+/Fe3+ ions in DMSO: H2O (1:1, v/v). The probe HQ-AMP was synthesized using a simple acid catalyst, Schiff base condensation, which involves the reaction between aldehyde and amine. This probe shows a significant fluorescence response towards Cu2+ and Fe3+ ions among the other alkaline earth metal ions. The HQ-AMP forms a 1:1 stoichiometry complex with a high binding constant for Cu2+ and Fe3+ ions with a low detection limit of 34 nM and 47 nM, respectively. Due to their strong intermolecular charge transfer properties, the probe HQ-AMP shows intense fluorescence at 488 nm upon excitation at 350 nm. The selective fluorescence quenching of probe HQ-AMP with Cu2+/Fe3+ ions shows static/dynamic quenching and their quenching constant of 1.93 × 10−8 and 2.06 × 10−8, respectively. Also, the probe shows the highest selectivity towards Cu2+/Fe3+ ions over the other tested metal ions.

An aggregation-induced emission photosensitizer with efficient singlet oxygen generation capacity for mitochondria targeted photodynamic therapy

A family of near-infrared (NIR) aggregation-induced emission (AIE) photosensitizers (PSs) were designed and synthesized to modulate the spectroscopic and photochemical properties of the contained donor-acceptor (D-A) units. Stronger intermolecular charge transfer (ICT) states were promoted by the synergistic action of benzothiadiazoles and quinolines, which accelerates intersystem crossing (ISC). The best NIR AIE-PS, BTQ, showed an extremely high 1O2 generation rate (5.6-fold of Rose Bengal) and highly efficient photodynamic killing of cancer cells. Furthermore, the mechanism by which mitochondria-targeted PSs produce large amounts of reactive oxygen species (ROS) triggering calcium ion (Ca2+) overload and opening of the mitochondrial permeability transition pore (mPTP), thereby disrupting mitochondria and leading to apoptosis, was demonstrated for the first time. This work provides an exciting benchmark for the molecular engineering of AIE-PSs targeting mitochondria and presented new insights of the development of fluorescence imaging guided photodynamic therapy (FL-G-PDT).

The effect of conjugation degree of aromatic carboxylic acids on electronic and photo-responsive behaviors of naphthalenediimide-based coordination polymers.

Three novel naphthalenediimide-based (NDI-based) coordination polymers (CPs), namely [Cd(3-PMNDI)(2,2'-BPDC)] (1), [Cd2(3-PMNDI)1.5(4,4'-BPDC)2(H2O)3]·DMF (2) and [Cd(3-PMNDI)(4,4'-SDC)] (3) (2,2'-H2BPDC = 2,2'-biphenyldicarboxylic acid, 4,4'-H2BPDC = 4,4'-biphenyldicarboxylic acid, 4,4'-H2SDC = 4,4'-stilbenedicarboxylic acid, 3-PMNDI = N,N'-bis(3-pyridylmethyl)-1,4,5,8-naphthalenediimide, and DMF = N,N'-dimethylformamide), have been designed and synthesized here from electron-deficient PMNDI (electron acceptors, EAs) and electron-rich aromatic carboxylic acids (electron donors, EDs) in the presence of cadmium ions. The introduction of aromatic carboxylic acids with different sizes and conjugation degrees leads to the generation of a two-dimensional (2D) layer in 1, a two-fold interpenetrated three-dimensional (3D) network in 2 and an eight-fold interpenetrated 3D framework in 3. Furthermore, the use of distinct electron-donating aromatic carboxylic acids and the consequent different numbers and strengths of lone pair-π and π-π interactions in the interfacial contacts of EDs/EAs give rise to distinct intermolecular charge transfer (ICT) and initial colors of the three CPs, and consequently cause different photoinduced intermolecular electron transfer (PIET) and distinguishing photo-responsive behaviors (weak photochromic performance for 1, excellent photochromic properties for 2 and non-photochromism for 3). This study indicates that an appropriate ICT is beneficial for PIET, but too weak or too strong ICT is not conducive to PIET, which provides an effective strategy for the construction of functional CPs with distinguishing photo-responsive properties through the subtle balance of ICT and PIET.

Synergistically Improving the Absorption, Energy Level, and Crystallization of PM6 by a Dicyanobenzothiadiazole Block-Based Terpolymer Strategy

The current top performing polymer solar cells (PSCs) are predominately based on the polymer donor material PM6 paired with Y-series small-molecule acceptors. For the limited improvement space for the Y-series acceptors, it is of great importance to explore strategies to optimize the molecular structure of PM6 for further elevation of the power conversion efficiencies (PCEs). Evidently, the terpolymer strategy is an effective method to improve the inherent properties of PM6 by introducing units with different electron states as building blocks in the copolymer backbone. In this work, a dicyanobenzothiadiazole (CNBT) group was selected and incorporated into the backbone of PM6 to form random terpolymers in a (D–A1)n–(D–A2)m structure with various CNBT contents. The electron-deficient CNBT group induced a strong intermolecular charge transfer, resulting in the rise of a red absorption band, which covered the absorption gap between PM6 and L8-BO around 700 nm. The high electron deficiency of CNBT groups also enabled a downshift in the highest occupied molecular orbital (HOMO) of PM6 for causing improvement of Voc. Furthermore, the high dipole moment of CNBT groups enhanced intermolecular aggregation, which helped to overcome the crystallization reduction effect of the terpolymer structures, leading to optimization of the thin-film morphology. The synergistically enhanced absorption, energy level matching, and crystallization tendency led to simultaneously increased Voc, Jsc, and FF, which all contributed to a significantly increased PCE of up to 18.01% compared with the PM6-based devices.

The nonlinear optical properties and noncovalent interactions of supramolecular Donor−acceptor−donor assemblies between molecular tweezers and fullerenes

The supramolecular donor−acceptor−donor (D−A−D) system were formed between the tweezer and C60 with strong intermolecular charge transfer interactions, which enhance the two-photon absorption (TPA) cross-section. Here, we would use density functional theory method to investigate three effects of molecular structures on the intermolecular interactions and the second order NLO properties of supramolecular complexes, including: (1) the effects of N atom substitution in tweezer (2) the effects of four extra benzene rings in tweezer (3) the effect of fullerene size. It was found that the substitution of N atoms and the addition of the four extra benzene rings to tweezer weakened the intermolecule interactions between fullerene and tweezer, suggesting that they did not enhance the electron-giving capacities of tweezers. While the fullerenes of larger size can form the stronger intermolecule interaction with tweezers.

Pagoda[5]arene with Large and Rigid Cavity for the Formation of 1∶2 Host–Guest Complexes and Acid/Base-Responsive Crystalline Vapochromic Properties

Pagoda[5]arene (P5), which is composed of five 2,6-dimethoxylanthracene (2,6-DMA) subunits bridged by methylene groups at 1,5 positions, was conveniently synthesized in 43% by trifluoroacetic acid ...

Host guest chemistry and supramolecular doping in triphenylamine-based covalent frameworks on Au(111).

The post-synthetic modification of covalent organic frameworks (COFs) via host-guest chemistry is an important method to tailor their electronic properties for applications. Due to the limited structural control in the assembly of two-dimensional surface-supported COFs, supramolecular networks are traditionally used at present for host-guest experiments on surfaces, which lack structural and thermal stability, however. Here, we present a combined scanning tunneling microscopy and density functional theory study to understand the host-guest interaction in triphenylamine-based covalently-linked macrocycles and networks on Au(111). These triphenylamine-based structures feature carbonyl and hydrogen functionalized pores that create preferred adsorption sites for trimesic acid (TMA) and halogen atoms. The binding of the TMA through optimized hydrogen-bond interactions is corroborated by selective adsorption positions within the pores. Band structure calculations reveal that the strong intermolecular charge transfer through the TMA bonding reduces the band gap in the triphenylamine COFs, demonstrating the concept of supramolecular doping by host-guest interactions in surface-supported COFs. Halogen atoms selectively adsorb between two carbonyl groups at Au hollow sites. The mainly dispersive interaction of the halogens with the triphenylamine COF leads to a small downshift of the bands. Most of the halogens change their adsorption position selectively upon annealing near the desorption temperature. In conclusion, we demonstrate evidence for supramolecular doping via post-synthetic modification and to track chemical reactions in confined space.

PEO/PVA/LiOH Solid Polymer Electrolyte Prepared via Ultrasound-assisted Solution Cast Method

ABSTRACT Most solid polymer electrolytes (SPEs) still suffer from low ionic conductivity at room temperature, which may be caused by the inhomogeneity of polymer blend and Li-salt. Here, polyethylene oxide (PEO), polyvinyl alcohol (PVA), and lithium hydroxide (LiOH) SPEs were prepared by an ultrasonic method to improve the ionic conductivity and shorten the synthesis time. This procedure has successfully yielded a flexible, transparent, and homogeneous SPEs, which were thermally stable at fairly high temperature as revealed from thermogravimetric analysis (TGA). These samples also showed relatively high ionic conductivity at room temperature with the highest conductivity of 1.25 × 10−4 S/cm and low activation energy of 0.253 eV demonstrated by sample with 2 wt% LiOH loading. Moreover, this sample was also stable in the measured voltage range, i.e., -5 to 5 V. DFT calculation showed that strong intermolecular charge transfer was present in the interaction between Li+ ion with PVA and PEO chain.

Highly Efficient Near‐Infrared Electroluminescence up to 800 nm Using Platinum(II) Phosphors

AbstractNear‐infrared organic light‐emitting diodes (NIR OLEDs) enable many unique applications ranging from night‐vision displays and photodynamic therapies. However, the development of efficient NIR OLEDs with a low efficiency roll‐off is still challenging. Here, a series of new heteroleptic Pt(II) complexes (1–4) flanked by both pyridyl pyrimidinate and functional azolate chelates are synthesized. The reduced ππ* energy gap of the pyridyl pyrimidinate chelate, and strong intermolecular interaction and high crystallinity in vacuum‐deposited thin films engender strong intermolecular charge transfer transition including metal–metal‐to‐ligand charge transfer; thereby, exhibiting efficient photoluminescence within 776–832 nm and short radiative lifetimes of 0.52–0.79 µs. Consequently, nondoped NIR‐emitting OLEDs based on these Pt(II) complexes are fabricated, to which Pt(II) complexes 2 and 4 give record high maximum external quantum efficiency of 10.61% at 794 nm and 9.58% at 803 nm, respectively. Moreover, low efficiency roll‐off is also observed, among which the device efficiencies of 2 and 4 are at least four times higher than that of the best NIR‐emitting OLEDs recorded at current density of 100 mA cm−2.

Design, Synthesis and Photophysical Properties of Chlorinated Small Molecule Non-fullerene Acceptor Based on Benzotriazole for Organic Solar Cells

A novel narrow band-gap chlorinated non-fullerene pentacyclic small molecule acceptor based on benzotriazole with extended absorption edge to the near-infrared (NIR) region, named BZIC-4Cl, was designed and synthesized. Through introducing multi-fused benzotriazole and IC-2Cl, BZIC-4Cl could maintain a lower optical bandgap of 1.38 eV with broad and efficient absorption band from 500 to 950 nm due to increased π−π interactions by the covalently locking thiophene and benzotriazole units. There is a stronger intermolecular charge transfer (ICT) effects between the BZTP core and IC-2Cl end-group. The purity and chemical structure of the acceptor, namely BZIC-4Cl, were tested by 1H NMR. Even though BZIC-4Cl showed slightly poor solubility in certain organic solvents, BZIC-4Cl showed broad and strong absorption with a narrow band-gap which can be matched with polymer donor for efficient organic solar cells.

Synthesis and Photophysical Properties of Small Molecule Donor Materials Based on Indacenodithieno[3, 2-b]Thiophene Core for Organic Solar Cells

We synthesized a small molecule donor material based on IDTT for solar cells, named C6S2ThBSeIDTT, which was obtained by IDTT-2SnMe3 and a capping fragment by a simple Stiller coupling reaction. Its structure and properties were HNMR. C6S2ThBSeIDTT was confirmed that it exhibited good solubility in conventional organic solvent. It can be found that strong intermolecular charge transfer (ICT) exists in the D-A-D-A-D conformation. It has been found to have broad and strong absorption by absorption spectroscopy with a medium wide band gap of 1.70 eV, and will well agree with fullerene acceptors such as PC60BM and PC71BM for efficient bulk heterojunction solar cells.

Density functional theory study on two D-π-A-type organic dyes containing different anchoring groups for dye-sensitized solar cells

The electronic structure and absorption spectra of two D-π-A-type organic dyes with different anchoring groups have been investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The effect of anchoring groups on the electronic absorption of the free dyes on (TiO2)9 has been studied for the two carbazole dyes (MK1 and MK2). Results from DFT calculations indicate that hydroxamic acid anchoring group in MK2 lead to much stronger intermolecular charge transfer and adsorption energies on (TiO2)9 cluster. The effect of four different XC functionals (B3LYP, ωB97xD, M06-2X, and CAM-B3LYP) on the transition energies has been tested in order to explore the valid functional for the studied system. The wavelength values from the ωB97xD/6-31+G** level of theory are in excellent agreement with experimental data so this functional was considered to calculate the electronic absorption of the two studied dyes. The highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), and the gap energy (H–L) of the studied dyes are slightly influenced by change of anchoring group. Results reveal that the LUMO energy levels of all studied dyes are higher than the conduction band (CB) of TiO2 (− 4.00 eV). Deprotonation process enhances the efficiency of dye-sensitized solar cells during decreasing adsorption energy of dyes with (TiO2)9 cluster.

Synthesis and Photophysical Properties of Aromatic Fused Ring Small Molecule Acceptor Materials Based on Two-dimensional indacenodithiazole for Organic Solar Cells

A new two-dimensional conjugated core unit 2DIDTz was synthesized based on indacenodithiazole with thiophene side chain. Then, a linear two-dimensional conjugated small molecule acceptor material, namely IDTzIID, based on 2DIDTz as core unit and (E)-1,1’-bis(2-ethylhexyl)-[3,3’-biindolinylidene]-2,2’-dione (IID) as end-groups was designed and synthesized through Still coupling reaction. There is a strong intermolecular charge transfer (ICT) between the IID and 2DIDTz. The structure and purity of the IDTzIID target compound was examined by 1H NMR. The IDTzIID showed good solvent properties in organic solvents. The IDTzIID showed wide and broad absorption with a band gap of 1.63 eV which can be matched with polymer donor materials for advanced organic solar cells.

Charge‐Transfer Complexes: Deep‐Red/Near‐Infrared Electroluminescence from Single‐Component Charge‐Transfer Complex via Thermally Activated Delayed Fluorescence Channel (Adv. Funct. Mater. 38/2019)

In article number 1903112, Liang-Sheng Liao, Chun-Sing Lee, and co-workers report the formation of dimeric single-component charge-transfer complexes (SCCTCs) by self-complexation of a donor-π-acceptor molecule (PIPAQ), wherein the strong intermolecular charge transfer leads to unusual deep-red/near-infrared thermally activated delayed fluorescence. Notably, PIPAQ can be applied in light-emitting devices as an emissive layer to realize unprecedented SCCTC-based electroluminescence.

Highly Efficient Thermally Activated Delayed Fluorescence via J-Aggregates with Strong Intermolecular Charge Transfer.

The development of high-efficiency and low-cost organic emissive materials and devices is intrinsically limited by the energy-gap law and spin statistics, especially in the near-infrared (NIR) region. A novel design strategy is reported for realizing highly efficient thermally activated delayed fluorescence (TADF) materials via J-aggregates with strong intermolecular charge transfer (CT). Two organic donor-acceptor molecules with strong and planar acceptor are designed and synthesized, which can readily form J-aggregates with strong intermolecular CT in solid states and exhibit wide-tuning emissions from yellow to NIR. Experimental and theoretical investigations expose that the formation of such J-aggregates mixes Frenkel excitons and CT excitons, which not only contributes to a fast radiative decay rate and a slow nonradiative decay rate for achieving nearly unity photoluminescence efficiency in solid films, but significantly decreases the energy gap between the lowest singlet and triplet excited states (≈0.3 eV) to induce high-efficiency TADF even in the NIR region. These organic light-emitting diodes exhibit external quantum efficiencies of 15.8% for red emission and 14.1% for NIR emission, which represent the best result for NIR organic light-emitting diodes (OLEDs) based on TADF materials. These findings open a new avenue for the development of high-efficiency organic emissive materials and devices based on molecular aggregates.

Dense, Subnano Phase of Clustered O2

Condensed O2 tends to form clusters, even with a long-range order. In particular, in solid oxygen, strong intermolecular charge transfer at high pressures leads to the formation of (O2)4 tetramers above 10 GPa, in the e-O2 phase, with weak O2–O2 chemical bonds. Indeed, e-O2 is entirely made of these tetramers. We conducted experimental investigations on strongly densified O2 in a different environment, that is to say in the form of a subnano phase build up within the 1D microchannels of a purely siliceous, inert zeolite, TON, at pressures of 0.5–20 GPa, by means of diamond anvil cells. Our X-ray diffraction and infrared and Raman spectroscopy results consistently show that oxygen forms clusters in this nanophase, above 10 GPa, similar to e-O2, except that the clusters are rather of the type of weakly bonded (O2)2 dimers in this case. Also, by analogy with bulk oxygen, we show that the O2 spin within the dimers departs from S = 1 toward lower values, upon increasing pressure. Our findings thereby add to the general view on essential properties of highly dense oxygen.

Vibrational spectra, dielectric properties, conductivity mechanisms and third order nonlinear optical properties of guanidinium 4-aminobenzoate

The frequency response of dielectric permittivity measurements at temperatures 35 °C and 100 °C suggests enhanced inherent optical quality and few defects in the crystal. The Cole-Cole plot shows the presence of grain and grain boundary, it is found that single relaxation is observed in the crystal. The ac and dc conductivity and dielectric behavior of the grown crystal were systemically investigated as a function of frequency and temperature. The third order nonlinear optical property extensively studied by z-scan technique revealed high third order nonlinearity in the form of self-defocusing and two-photon absorption with saturable absorption. The strong intermolecular charge transfer interaction evident from NBO and AIM studies confirms the NLO property of the material. The detailed vibrational assignments were carried out on the basis of potential energy distribution (PED) analysis and scaled quantum mechanical force field calculation using MOLVIB program. The red shifted NH stretching wavenumbers and the broadening of corresponding bands in the solid state as well as the gas phase spectra, optimized molecular geometry and NBO analysis have confirmed the presence of N-H⋯O hydrogen bonding in G4AB.

Star‐Shaped and Fused Electron Acceptors based on C3h‐Symmetric Coplanar Trindeno[1, 2‐b: 4, 5‐b′: 7, 8‐b′′]trithiophene Core for Non‐Fullerene Solar Cells

Two new star-shaped and fused electron acceptors, TITT-3IC and TITT-3ICF have been designed and synthesized, which consist of a C3h -symmetric coplanar trindeno[1, 2-b: 4, 5-b': 7, 8-b'']trithiophene (TITT) as the central core and 3-(dicyanomethylidene)indan-1-one and 2-(5,6-difluoro-3-oxo-2,3-dihydro-1H-inden-1-ylidene) malononitrile as the peripheral electron-withdrawing groups, respectively. With the large coplanar configuration and electron-rich nature of π-conjugated backbone, these two acceptors exhibit strong intermolecular charge transfer absorption in the region of 500-650 nm with the optical band gaps around 1.9 eV. Relative to TITT-3IC, TITT-3ICF shows the downshifted LUMO level and the slightly redshifted absorption with the higher molar extinction coefficient due to the stronger electron-withdrawing effect of fluorination. When blending with PTB7-Th, the TITT-3ICF-based device displays a higher power conversion efficiency (PCE) of 4.26 % than the TITT-3IC-based device (PCE=3.87 %). Comparing with the TITT-3IC-based device, the increased short circuit current (JSC ) and fill factor (FF) are responsible for the higher PCE value of the TITT-3ICF-based device, which benefits from its strong and redshifted absorption for light harvesting and proper phase separation morphology for effective exciton dissociation and charge transport. This work demonstrates that as an alternative electron-donating core, TITT will be promising in designing star-shaped non-fullerene materials.

A Novel Linking Strategy of Using 9,10-Dihydroacridine to Construct Efficient Host Materials for Red Phosphorescent Organic Light-Emitting Diodes.

Three novel 9,10-dihydroacridine derivatives, 4'-(10-methyl-9,9-diphenyl-9,10-dihydroacridin-4-yl)[1,1'-biphenyl]-4-carbonitrile (MeAcPhCN), 4'-(9,9,10-triphenyl-9,10-dihydroacridin-4-yl)[1,1'-biphenyl]-4-carbonitrile (PhAcPhCN), and 5-[4-(9,9,10-triphenyl-9,10-dihydroacridin-4-yl)phenyl]picolinonitrile (MeAcPyCN), were prepared by the attachment of [1,1'-biphenyl]-4-carbonitrile or 5-phenylpicolinonitrile to the 4-position of 9,10-dihydroacridine. This special linking strategy limited the conjugation length, maintained the triplet energy, and inhibited the intermolecular charge-transfer (ICT) characteristics of these compounds. Notably, the enhanced accepting strength of the picolinonitrile segment relative to that of benzonitrile led to relatively strong ICT characteristics, a low energy gap, and a low triplet energy for MeAcPyCN. The thermal, photophysical, electrochemical, and electroluminescent properties of these host materials were studied systematically. Consequently, (acetylacetonato)bis(2-methyldibenzo[f,h]quinoxaline)iridium(III) [Ir(MDQ)2 (acac)]-based red phosphorescent organic light-emitting diodes (PHOLEDs) were fabricated with these three host materials. As a result, the device hosted by MeAcPhCN showed good device performance with a maximum external quantum efficiency of 20.5 %.

MD/QC Simulation of the Structure and Spectroscopic Properties of α-NPD-BAlq Exciplexes at an α-NPD/BAlq Interface in OLEDs

The structure and spectroscopic properties of exciplexes formed at an interface between a hole-transporting layer of N,N′-di(naphthalen-2-yl)-N,N′-diphenyl-benzidine (α-NPD) and an electron transporting layer of bis(2-methyl-8-quinolinato)(4-phenylphenolato)-aluminum (BAlq) in an OLED are investigated by multiscale (molecular dynamics, MD, and quantum chemistry, QC) simulations. Four α-NPD–BAlq pairs with different orientations of components are selected from the central 5-nm slab with the interface for subsequent QC calculations. Calculations for these pairs are performed within DFT/PBE0 and DFT/BHandHLYP approaches for the ground state and TDDFT/PBE0 and TDDFT/BHandHLYP approaches for the excited state with inclusion of D3BJ dispersion corrections. The calculated binding energies of the complexes are in the range from –19.0 to –24.7 kcal/mol in the ground state and from –21.9 to –34.1 kcal/mol in the excited state. The calculated S1 excited states are characterized by strong intermolecular charge transfer, and the corresponding S1→S0 transition energies are in good agreement with the available experimental data.