Molecular Rigidity Research Articles

Molecular Geometry-Directed Self-Recognition in the Self-Assembly of Giant Amphiphiles.

Three sets of polyoxometalate (POM)-based amphiphilic hybrid macromolecules with different rigidity in their organic tails are used as models to understand the effect of molecular rigidity on their possible self-recognition feature during self-assembly processes. Self-recognition is achieved in the mixed solution of two structurally similar, sphere-rigid T-shape-linked oligofluorene(TOF4 ) rod amphiphiles, with the hydrophilic clusters being Anderson (Anderson-TOF4 ) and Dawson (Dawson-TOF4 ), respectively. Anderson-TOF4 is observed to self-assemble into onion-like multilayer structures and Dawson-TOF4 forms multilayer vesicles. The self-assembly is controlled by the interdigitation of hydrophobic rods and the counterion-mediated attraction among charged hydrophilic inorganic clusters. When the hydrophobic blocks are less rigid, e.g., partially rigid polystyrene and fully flexible alkyl chains, self-recognition is not observed, attributing to the flexible conformation of hydrophobic molecules in the solvophobic domain. This study reveals that the self-recognition among amphiphiles can be achieved by the geometrical limitation of the supramolecular structure due to the rigidity of solvophobic domains.

Electrochemical test of flexibility of pyridine terminated molecular rods

A family of seven symmetrical molecular rods, which are sharing 4-ethynylpyridyl terminal groups and differ in the structure of the linker have been investigated. Although structurally related they show unique electrochemical behavior, which clearly correlates with their conformational flexibility. Two flexible compounds are reduced by two electrons. Their reduction yields intensive charge transfer UV-vis absorption bands and is accompanied by characteristic EPR spectra. In contrast, all conformationally rigid structures are reduced by four electrons and do not yield neither charge transfer bands nor distinct EPR signals. Simple irreversible voltammetry of all derivatives is similar to the reduction of 4-ethynylpyridine at -2.1 V. The experimental observations were supported by the extensive DFT calculations. Electrochemical techniques proved to be valuable in distinction between molecular rigidity and flexibility.

Fusion of Multi-Resonance Fragment with Conventional Polycyclic Aromatic Hydrocarbon for Nearly BT.2020 Green Emission.

Herein, we report a general strategy for achieving ultra-pure green emissions by suppressing the shoulder peaks in the emission spectra of conventional polycyclic aromatic hydrocarbons (PAHs). Through precise synthetic fusion of multi-resonance (MR) fragments with conventional PAH, extended π-conjugation lengths, increased molecular rigidity, and reduced vibrational frequency could be simultaneously realized. The proof-of-concept emitters exhibited ultra-pure green emissions with dominant peaks at ca. 521 nm, photoluminescence quantum yields that are greater than 99 %, a small full-width-at-half-maximum of 23 nm, and CIE coordinates of (0.16, 0.77). The bottom-emitting organic light-emitting diode (OLED) exhibited a record-high CIEy value of 0.74 and a high maximum external quantum efficiency of 30.5 %. The top-emitting OLED not only achieved a BT.2020 green color (CIE: 0.17, 0.78) for the first time but also showed superior performance among all green OLED devices, with a current efficiency of 220 cd A- .

Fusion of Multi‐Resonance Fragment with Conventional Polycyclic Aromatic Hydrocarbon for Nearly BT.2020 Green Emission

AbstractHerein, we report a general strategy for achieving ultra‐pure green emissions by suppressing the shoulder peaks in the emission spectra of conventional polycyclic aromatic hydrocarbons (PAHs). Through precise synthetic fusion of multi‐resonance (MR) fragments with conventional PAH, extended π‐conjugation lengths, increased molecular rigidity, and reduced vibrational frequency could be simultaneously realized. The proof‐of‐concept emitters exhibited ultra‐pure green emissions with dominant peaks at ca. 521 nm, photoluminescence quantum yields that are greater than 99 %, a small full‐width‐at‐half‐maximum of 23 nm, and CIE coordinates of (0.16, 0.77). The bottom‐emitting organic light‐emitting diode (OLED) exhibited a record‐high CIEy value of 0.74 and a high maximum external quantum efficiency of 30.5 %. The top‐emitting OLED not only achieved a BT.2020 green color (CIE: 0.17, 0.78) for the first time but also showed superior performance among all green OLED devices, with a current efficiency of 220 cd A−.

Molecular structure insight into the tribological behavior of sulfonate ionic liquids as lubricants for titanium alloys

The wide industrial application of titanium alloys requires lubricating materials with superior performance. Although ionic liquids have been recognized as potential choices for excellent lubricants, research on their tribological properties as applied to titanium alloys is not mature and systematic. In this work, a series of halogen-free sulfonate IL lubricants with different anions and cations were designed, synthesized, and applied to the titanium alloy (Ti-6Al-4V) friction pairs. From the perspective of molecular structure, the influencing factors on their physicochemical properties (thermal stability, viscosity) and tribological performances (friction-reducing and anti-wear performances) were explored, including the influences derived from their active element, chain length, molecular rigidity and branched chain structure. The lubricating mechanism contributed by the IL molecules and the Ti surfaces during sliding were analyzed by means of SEM, XPS, ECR and QCM. The results showed that physical adsorption and tribo-chemical reactions were involved during the sliding process. And the lubricating performances of the synthesized ILs may largely depend on their ability to form physical/chemical adsorption films on the titanium interfaces. The rigid benzene ring structure and flexible alkyl chain are conducive to strengthening the stability and efficiency of the formed interfacial tribo-film.

Polycyclic phenazine-derived rigid donors construct thermally activated delayed fluorescence emitters for highly efficient orange OLEDs with extremely low roll-off

Two new thermally activated delayed fluorescence (TADF) molecules, tBuInPz-BO and InPz-BO, are constructed via connecting novel rigid polycyclic phenazine-derived donors with oxygen-bridged boron acceptor. Both emitters exhibit fast reverse intersystem crossing rates and high photoluminescence quantum yields, owing to the high molecular structural rigidity. As a result, the orange organic light-emitting diode (OLED) fabricated with tBuInPz-BO shows a maximum external quantum efficiency (EQEmax) of 22.0% with the electroluminescence peak at 585 nm. Moreover, the device displays extremely low efficiency roll-off. At high luminance of 1000 and 10000 cd/m2, the EQE values still maintain a high level of 20.2% and 14.8%, respectively, achieving state-of-the-art electroluminescence performance among TADF-based orange OLEDs. This work reveals the great potential of the new phenazine-derived donors for constructing highly efficient TADF emitters.

High-sensitivity sensor array base on molecular design and machine learning for amine differentiation in exhaled vapor

• A sensor array which can classify pathological biomarkers of amines is provided. • By molecular backbone rigidity together with multiple hydrogen-bonding acceptor and aromatic terminal structure tuning, the difference interactions between molecules and multiple amines are realized. • Through molecular design and machine learning, the detection and recognition of ppb concentration of amine/ammonia at room temperature with an accuracy of 90% by the sensor array are achieved. Nowadays, the studies on the diagnosis of diseases by exhaled gas mostly focus on single markers. In fact, there are biomarkers with similar properties but corresponding to different diseases. The present sensing techniques still cannot achieve the multi-label classification of the targets simultaneously. Through introducing multiple hydrogen bond receptors and adjusting of the aromatic ring end group, the interaction strength modulation between target molecules and sensor array was realized. The sensor responses related to molecular structure can be used as the characteristic of the detection. By the machine learning, the different types of amines are well identified. It is worth mentioning that this method can also distinguish mixed amines ranging any concentration in ppm-ppb, which can be used in breath analyzer. The recognition of the mixed ammonia / amine gases is achieved at room temperature with an accuracy of 90%. The combination of molecular design and machine learning strategy can improve the selectivity of sensor array, which also provides a new idea for the design of sensor array that can be used in rapid, convenient, non-invasive and cost-effective exhalation diagnosis.

Globally rigid powers of graphs

The characterization of rigid graphs in Rd for d≥3 is a major open problem in rigidity theory. The same holds for globally rigid graphs. In this paper our goal is to give necessary and/or sufficient conditions for the (global) rigidity of the square G2 (and more generally, the power Gk) of a graph G in Rd, for some values of k,d. Our work is motivated by some results and conjectures of M. Cheung and W. Whiteley from 2008, the Molecular Theorem of N. Katoh and S. Tanigawa from 2011, which settled the case of rigidity for k=2,d=3, and the potential applications in molecular conformation and sensor network localization.We first consider the case when k=d and characterize those graphs G for which Gd is globally rigid in Rd, for all d≥1, and then focus on the case when k=d−1. We provide a new, direct proof for the 3-dimensional bar-and-joint version of the Molecular Theorem (d=3) and a necessary condition for the rigidity of Gd−1 in Rd, for all d≥3. We conjecture that this condition is also sufficient.The global rigidity of square graphs in R3 is still an open problem. We formulate a Molecular Global Rigidity Conjecture, which proposes a combinatorial characterization of globally rigid square graphs in terms of vertex partitions and edge count conditions. We prove that the condition is necessary. For the general case we give a best possible connectivity based sufficient condition by showing that if G is 3-edge-connected then Gd−1 is globally rigid in Rd, for all d≥3.Our results imply affirmative answers to the conjectures of M. Cheung and W. Whiteley in two special cases.

A novel orange-red thermally activated delayed fluorescence emitter with high molecular rigidity and planarity realizing 32.5% external quantum efficiency in organic light-emitting diodes.

Simultaneous optimization of photoluminescence quantum yield (ΦPL) and horizontally oriented dipoles (Θ‖) is considerably challenging for orange and red thermally activated delayed fluorescence (TADF) emitters, due to the conflicts between enhancing molecular rigidity and improving molecular planarity. Herein, a novel orange-red TADF emitter 10-(dipyrido[3,2-a:2',3'-c]phenazin-11-yl)-10H-spiro[acridine-9,9'-fluorene] (SAF-2NP) was constructed with a donor-acceptor structure. The highly rigid donor and acceptor segments ensure the overall rigidity of the emitter. More importantly, the quasi-coplanar structure between the acceptor and the fluorene moiety in the donor unit enlarges the molecular plane without weakening rigidity. Consequently, SAF-2NP exhibited extremely high ΦPL and Θ‖ of 99% and 85%, respectively. The optimal organic light-emitting diode using SAF-2NP as the emitter and 4,4'-di(9H-carbazol-9-yl)-1,1'-biphenyl (CBP) as the host demonstrated an unparalleled external quantum efficiency of 32.5% and a power efficiency of 85.2 lm W-1 without any extra light extraction structure. This work provides a feasible strategy to establish efficient orange and red TADF emitters with both high rigidity and planarity.

Robust singlet fission process in strong absorption π-expanded diketopyrrolopyrroles.

Singlet fission (SF) has drawn tremendous attention as a multiexciton generation process that could mitigate the thermal loss and boost the efficiency of solar energy conversion. Although a SF-based solar cell with an EQE above 100% has already been fabricated successfully, the practical efficiency of the corresponding devices is plagued by the limited scope of SF materials. Therefore, it is of great importance to design and develop new SF-capable compounds aiming at practical device application. In the current contribution, via a π-expanded strategy, we presented a new series of robust SF chromophores based on polycyclic DPP derivatives, Ex-DPPs. Compared to conventional DPP molecules, Ex-DPPs feature strong absorption with a fivefold extinction coefficient, good molecular rigidity to effectively restrain non-radiative deactivation, and an expanded π-skeleton which endow them with well-suited intermolecular packing geometries for achieving efficient SF process. These results not only provide a new type of high-efficiency SF chromophore but also address some basic guidelines for the design of potential SF materials targeting practical light harvesting applications.

UV, FL and IR spectroscopic analysis of N-confused meso-tetra(methoxyphenyl)porphyrins

UV, FL and IR spectra of isomer A (in DCM) and isomer B (in DMAc) of N-confused 5,10,15,20-tetra([Formula: see text]-methoxyphenyl)porphyrin ([Formula: see text]-isomer, 1), N-confused 5,10,15,20-tetra([Formula: see text]-methoxyphenyl)porphyrin ([Formula: see text]-isomer, 2) and N-confused 5,10,15,20-tetra([Formula: see text]-methoxyphenyl)porphyrin ([Formula: see text]-isomer, 3) were investigated. Significant red shifts are observed from [Formula: see text]-isomer (1) to [Formula: see text]-isomer (3) in UV-vis absorption and fluorescence spectra. The fluorescence lifetime ([Formula: see text] of isomer A and isomer B of the samples (1, 2 and 3) are ca. 1.39[Formula: see text]1.79 ns and 1.68[Formula: see text]2.09 ns, respectively. In addition, the order of fluorescence quantum yield for isomer A is 1 >2 > 3, but for isomer B it is 1 < 3 <2. The isomer B of 2shows the strongest emission in accord with the strongest absorption. The isomer A of 1shows the strongest emission with the fluorescence quantum yield of 0.045, which is nearly double that of 3. The introduction of the methoxy group at the orthoposition increases steric hindrance, the molecular rigidity and the flow of [Formula: see text]-electron, thereby favourable to the fluorescence enhancement. The IR absorption peaks of 1, 2 and 3 were investigated and empirically assigned. The effects of the position of the substituents on the absorption frequency were also discussed. The absorption frequency of the C=C phenyl stretching in plane changed obviously by conjugative effect and steric effect when the methoxy group was at the orthoormetaposition in comparison with paraposition.

Aramid-film pH sensitive fluorescence enhancement based on benzimidazole intermolecular hydrogen bonds

The aramid-film containing benzimidazole units was synthesized, and its pH sensitive fluorescence enhancement effect was investigated. After surface-treated by acidic ethanol solution (pH 1), the aramid film exhibits noticeable emissive enhancement as high as 33 times than the blank sample. The fluorescence lifetimes of aramid films increase significantly from 0.9 × 10−10 s to 8.2 × 10−10 s. The driving force is ascribed to the decrease of nonradiative transition probability, which comes from the strengthening molecular rigidity of phenyl benzimidazole chromophore within the polymer chains, induced by hydrogen bonds between N-H in benzimidazole group and C=O in amide group. The hydrogen-bond effect is thoroughly proved through examining the repeating molecular units of the aramid polymer chains by the methods of XRD, UV–vis, photoluminescence, molecular simulation, SEM and etc. This pH sensitive fluorescence change should have great potential in the sensor-device design of NH3, heavy metal ions or other systems due to the subsequent fluorescence quench effect, because of the excellent mechanical and processability of aramid polymers.

In Situ RheoNMR Correlation of Polymer Segmental Mobility with Mechanical Properties during Hydrogel Synthesis.

Understanding polymer gelation over multiple length‐scales is crucial to develop advanced materials. An experimental setup is developed that combines rheological measurements with simultaneous time‐domain 1H NMR relaxometry (TD‐NMR) techniques, which are used to study molecular motion (<10 nm) in soft matter. This so‐called low‐field RheoNMR setup is used to study the impact of varying degrees of crosslinking (DC) on the gelation kinetics of acrylic acid (AAc) and N,N′‐methylene bisacrylamide (MBA) free radical crosslinking copolymerization. A stretched exponential function describes the T 2 relaxation curves throughout the gelation process. The stretching exponent β decreases from 0.90 to 0.67 as a function of increasing DC, suggesting an increase in network heterogeneity with a broad T 2 distribution at higher DC. The inverse correlation of the elastic modulus G′ with T 2 relaxation times reveals a pronounced molecular rigidity for higher DC at early gelation times, indicating the formation of inelastic, rigid domains such as crosslinking clusters. The authors further correlate G′ with the polymer concentration during gelation using a T 1 filter for solvent suppression. A characteristic scaling exponent of 2.3 is found, which is in agreement with theoretical predictions of G′ based on the confining tube model in semi‐dilute entangled polymer solutions.

Manipulation of Triplet Excited States for Long‐Lived and Efficient Organic Afterglow

AbstractIn organic systems, it is very challenging to simultaneously achieve long afterglow lifetimes (τAG) and high afterglow efficiency (ΦAG). Here, luminescent dopants which feature a small rate of phosphorescence decay (kP) and modest rate of reverse intersystem crossing (kRISC) are designed and knr + kq values (nonradiative decay and quenching) of triplet excited states are suppressed by all means that include increasing molecular rigidity of luminescent dopants, screening organic matrices to strongly inhibit intramolecular motions of luminescent dopants, and deuteration of the luminescent dopants. Organic matrices are selected with large dipole moments to stabilize the singlet excited states of luminescent dopants via dipole–dipole interactions, reduce singlet–triplet splitting energy, and thus enhance ΦISC, leading to significant population of triplet excited states. Thermally activated delayed fluorescence mechanism is also used with modest kRISC to harvest triplet energies, significantly improve ΦAG to 64%, and maintain long τAG &gt; 1.0 s. The obtained materials display intense afterglow brightness, excellent processability, and temperature‐sensing function.

Synthesis and Spectral Characterisation of (E)-3-(3-(4 (Dimethylamino)Phenyl)Acrylo-yl)-4-Hydroxy-2H-Chromen-2-One and Their Antibacterial Activity and Acetylcholinesterase Inhibition

A new coumarin derivative, (E)-3-(3-(4-(dimethylamino) phenyl) acrylo-yl)-4-hydroxy-2H-chromen-2-one (3), was synthesized by the condensation of 3-acetyl-4-hydroxycoumarin (1) with 4-N,N-dimethylaminobenzaldehyde (2) in the presence of piperidine in ethanol. The structure of the synthesized compound was characterized using spectroscopic data (IR and 1H NMR) and elemental analysis. The antimicrobial properties and acetylcholinesterase inhibition activity (AChEI) of coumarin 3 were investigated, with the highest observed AChEI activity providing 48.25% inhibition. The electronic absorption and emission spectra revealed that 3 exists as two, main keto-enol tautomers. The ratios of these tautomers in both protic and aprotic solvents with different polarities and dielectric constants were calculated. The fluorescence of coumarin 3 was enhanced upon increasing the medium viscosity, which was due to the resultant molecular rigidity. This criterion was further investigated using DNA, whereby 3 showed enhanced fluorescence upon its uptake in DNA grooves and was therefore tested as a novel DNA fluorescent stain.

Nanoscale \u03c0-conjugated ladders

It is challenging to increase the rigidity of a macromolecule while maintaining solubility. Established strategies rely on templating by dendrons, or by encapsulation in macrocycles, and exploit supramolecular arrangements with limited robustness. Covalently bonded structures have entailed intramolecular coupling of units to resemble the structure of an alternating tread ladder with rungs composed of a covalent bond. We introduce a versatile concept of rigidification in which two rigid-rod polymer chains are repeatedly covalently associated along their contour by stiff molecular connectors. This approach yields almost perfect ladder structures with two well-defined π-conjugated rails and discretely spaced nanoscale rungs, easily visualized by scanning tunnelling microscopy. The enhancement of molecular rigidity is confirmed by the fluorescence depolarization dynamics and complemented by molecular-dynamics simulations. The covalent templating of the rods leads to self-rigidification that gives rise to intramolecular electronic coupling, enhancing excitonic coherence. The molecules are characterized by unprecedented excitonic mobility, giving rise to excitonic interactions on length scales exceeding 100 nm. Such interactions lead to deterministic single-photon emission from these giant rigid macromolecules, with potential implications for energy conversion in optoelectronic devices.

Blood bank storage of red blood cells increases RBC cytoplasmic membrane order and bending rigidity.

Blood banks around the world store blood components for several weeks ensuring its availability for transfusion medicine. Red blood cells (RBCs) are known to undergo compositional changes during storage, which may impact the cells’ function and eventually the recipients’ health. We extracted the RBC’s cytoplasmic membrane (RBCcm) to study the effect of storage on the membranes’ molecular structure and bending rigidity by a combination of X-ray diffraction (XRD), X-ray diffuse scattering (XDS) and coarse grained Molecular Dynamics (MD) simulations. Blood was stored in commercial blood bags for 2 and 5 weeks, respectively and compared to freshly drawn blood. Using mass spectrometry, we measured an increase of fatty acids together with a slight shift towards shorter tail lengths. We observe an increased fraction (6%) of liquid ordered (lo) domains in the RBCcms with storage time, and an increased lipid packing in these domains, leading to an increased membrane thickness and membrane order. The size of both, lo and liquid disordered (ld) lipid domains was found to decrease with increased storage time by up to 25%. XDS experiments reveal a storage dependent increase in the RBCcm’s bending modulus κ by a factor of 2.8, from 1.9 kBT to 5.3 kBT. MD simulations were conducted in the absence of proteins. The results show that the membrane composition has a small contribution to the increased bending rigidity and suggests additional protein-driven mechanisms.

Modeling of viscoelastic behavior of a shape memory polymer blend

AbstractShape memory effect (SME) of polymers is a property that concerns both, macroscopic and microscopic changes. The variation of internal polymer properties such, as molecular weight (Mw), rigidity, and viscoelasticity could alter its SME. In this study, a bi‐parabolic model with six parameters is used to describe the viscoelastic behavior of a shape memory polymer (SMP) blend (40% poly(caprolactone), PCL/60% Styrene–Butadiene–Styrene) with different PCL Mw. These parameters are determined using the Cole–Cole method. Modeling curves (E″ = f (E′)) will be then compared to experimental data from dynamical mechanical analysis (DMA) tests. It is shown that the bi‐parabolic model predicts well the behavior of the SMP mixture for different Mw of PCL. Afterwards, the evolution of the model parameters with the Mw of PCL is investigated. It is revealed that, when Mw of PCL drops, the relaxation modulus E0 increases. This result proves that the rigidity of the SMP blend rises with Mw declines.

Rational Utilization of Intramolecular Hydrogen Bonds to Achieve Blue TADF with EQEs of Nearly 30% and Single Emissive Layer All-TADF WOLED.

A series of highly efficient blue thermally activated delayed fluorescence (TADF) compounds, SON-Cz, SON-tBuCz, and SON-PhCz, were developed. Pyridinyl was introduced as the bridging unit between carbazole donors and sulfone acceptor. Intramolecular hydrogen bonds between the pyridine N atom and carbazole H atoms were detected in single crystals, which suppressed the twisting of carbazole rings and dramatically increased the molecular rigidity. At the same time, tert-butyl or phenyl were incorporated at the 3,6-sites of carbazole ring to tune electron donating ability or enlarge HOMO delocalization. All these hydrogen bonds featured TADF compounds exhibited much improved photoluminescence quantum yields (PLQYs) and excellent efficiencies in their doped blue organic light-emitting diodes. In particular, SON-tBuCz and SON-PhCz exhibited the maximum external quantum efficiencies (EQEs) of 29.59% and 28.22% with CIE coordinates of (0.17, 0.22) and (0.21, 0.36), respectively. The excellent performance benefits from the carbazole structure modification and the intramolecular hydrogen bonds, which bring more rigid structures and eliminate nonradiative transitions. Furthermore, a single emissive layer all-TADF white OLED was fabricated using SON-tBuCz as the blue emitter and 4CzTPN-Ph as the orange emitter to give an EQE of 23.51% with a high CRI of 71, which is among the top efficiencies ever reported for all-TADF WOLEDs so far.

The influence of fluorine terminal group and flexible spacers on properties of the liquid crystal dimers

ABSTRACT Two series of symmetric LC dimers with the same rigid group and different fluorine terminal group (F and F3C) have been synthesised by varying the length of flexible spacers, termed 1 F series (1 F-4, 1 F-6, 1 F-8) and 3 F series (3 F-4, 3 F-6, 3 F-8). Chemical structures and LC properties of the six symmetric LC dimers were characterised by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance hydrogen spectrometer (1H NMR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and polarised optical microscopy (POM). The 1 F series dimers only show nematic phase. While for 3 F series, smectic phase appeared, and with the increase of flexible spacers, the smectic phase is dominant. For the formation of smectic phase of 3 F series, the larger intermolecular transverse force coming from CF3 may be the driving force, and the long flexible spacer makes it possible. The melting temperatures of the 1 F series and 3 F series gradually decrease as the length of the flexible spacer increases, respectively, indicating that molecular rigidity has a greater influence on the melting temperatures. The melting temperatures of the 3 F series dimers decrease faster, which may attribute to the influence of CF3 on the conformation of the dimers.