Twisted Molecule Research Articles

Unravelling the Competition between Internal Conversion and Intersystem Crossing in Twisted molecule 9‐Phenylacridine by Femtosecond Time‐resolved Spectroscopy

Abstract9‐Phenylacridine (9‐PA) is an important acridine‐based medicine that has been proven to possess significant anticancer activity and can be used as a photodynamic therapy (PDT) agent. Meanwhile, the possible twisting of the C−C single bond at the C9 position after photo‐excitation makes it a potential probe responsive to changes in the viscosity of living cells. However, the photophysical properties of 9‐PA is poorly understood. In this study, we utilized femtosecond time‐resolved spectroscopy combined with quantum chemical calculation methods to investigate the excited state dynamics of 9‐PA in solutions with different viscosities. Notably, we demonstrated that the viscosity could strongly influence the deactivation pathway of the initially populated S1 (ππ*) state of 9‐PA. In low‐viscosity solutions, the single bond at the C9 could twist after photo‐excitation, leading to a conformation that shows efficient intersystem crossing. However, such process is suppressed in high‐viscosity solutions, resulting a ~2.5 times higher internal conversion (IC) yield. A full picture of the excited state deactivation mechanism of 9‐PA is proposed.

Quantification of chirality based on electric toroidal monopole.

Chirality ubiquitously appears in nature; however, its quantification remains obscure owing to the lack of microscopic description at the quantum-mechanical level. We propose a way of evaluating chirality in terms of the electric toroidal monopole, a practical entity of time-reversal even pseudoscalar (parity-odd) objects reflecting relevant electronic wave functions. For this purpose, we analyze a twisted methane molecule at the quantum-mechanical level, showing that the electric toroidal monopoles become a quantitative indicator for chirality. In the twisted methane, we clarify that the handedness of chirality corresponds to the signof the expectation value of the electric toroidal monopole and that the most important ingredient is the modulation of the spin-dependent imaginary hopping between the hydrogen atoms, while the relativistic spin-orbit coupling within the carbon atom is irrelevant for chirality.

Realizing mechano-tunable dual emission in a twisted thianthrene derivative

The twisted molecule, TATPO, which exhibited dual emissions of fluorescence (FL) and room-temperature phosphorescence (RTP) in both crystal types, were designed, synthesized and characterized. The dual-emissive bands were combined by fluorescence (ca. 439 nm) and phosphorescence (ca. 514 nm). Intriguingly, these two kinds of luminescence ratios (FL and RTP) can be tunable by external stimuli, such as grinding or fuming. Experimental and theoretical studies have shown that twisted molecular structure and the folded dihedral angle of thianthrene can promote spin-orbit coupling (SOC) and thus enhance phosphorescence. In addition, the folded dihedral angle of thianthrene group is the main reason that this molecule could realize tunable luminescence between FL and RTP. This work not only described a twisted molecule for pure organic multifunctional materials with mechanochromic luminescence properties, but also provided a novel strategy to design stimuli-responsive materials with tunable FL/RTP ratios.

Molecular Engineering of NIR-II/IIb Emitting AIEgen for Multimodal Imaging-Guided Photo-Immunotherapy.

In view of the great challenges related to the complexity and heterogeneity of tumors, efficient combination therapy is an ideal strategy for eliminating primary tumors and inhibiting distant tumors. A novel aggregation-induced emission (AIE) phototherapeutic agent called T-TBBTD is developed, which features a donor-acceptor-donor (D-A-D) structure, enhanced twisted molecule conformation, and prolonged second near-infrared window (NIR-II) emission. The multimodal imaging function of the molecule has significance for its treatment time window and excellent photothermal/photodynamic performance for multimode therapy. The precise molecular structure and versatility provide prospects for molecular therapy for anti-tumor applications. Fluorescence imaging in the NIR-II window offers advantages with enhanced spatial resolution, temporal resolution, and penetration depth. The prepared AIE@R837 NPs also have controllable performance for antitumor photo-immunotherapy. Following local photo-irradiation, AIE@R837 NPs generate abundant heat, and 1 O2 directly kills tumor cells, induces immunogenic cell death (ICD) as a photo-therapeutic effect, and releases R837, which enhances the synergistic effect of antigen presentation and contributes to the long-lasting protective antitumor immunity. A bilateral 4T1 tumor model revealed that this photo-immunotherapy can eliminate primary tumors. More importantly, it has a significant inhibitory effect on distant tumor growth. Therefore, this method can provide a new strategy for tumor therapy.

Triazole-induced planarization of a twisted tetrazole-based molecule towards energetic materials with improved thermostability and insensitivity.

Pursuing the structural planarization of energetic materials is an efficient method for achieving improved performance. Although many planar energetic molecules have been prepared so far, the innovation of advanced planar explosives still relies on the scientific intuition, experience and trial-and-error of researchers. Now, a triazole-induced planarization strategy is proposed based on the regulation of aromaticity, charge distribution, and hydrogen bonds. The incorporation of a triazole ring into the non-planar molecule 5-amino-1-nitriminotetrazole (VII) results in a planar energetic material named N-[5-amino-1-(1H-tetrazol-5-yl)-1H-1,2,4-triazol-3-yl]nitramide (3). Compared with VII (Td = 85 °C; IS < 0.25 J; FS < 5 N), 3 shows remarkably improved thermal stability (Td = 145 °C) and reduced sensitivities (IS = 20 J; FS > 360 N). The variation of thermal stability and mechanical sensitivity from VII to 3 reflects the effectiveness and superiority of the planarization strategy. Benefiting from the properties of 3, its energetic salt 5 exhibits excellent overall performance (Dv = 9342 m s-1; P = 31.6 GPa; Td = 201 °C; IS = 20 J; FS = 360 N), which is comparable to that of HMX. Moreover, the triazole-induced planarization strategy may serve as a guide for exploring advanced energetic materials.

Highly broadband NLO response of acceptor–donor–acceptor materials with a planar conformation

The third-order NLO properties of A–D–A molecules originally derived from organic photovoltaic (OPV) devices are studied. The results show that NLO performance of planar molecule (O-IDTBR) is better than that of twisted molecule (IDFBR) in solution or film state.

Synthesis and characterization of a twisted tri-sulfur-doped polycyclic aromatic hydrocarbon

Polycyclic aromatic hydrocarbons (PAHs) generally refer to aromatic compounds containing two or more fused benzene rings. PAHs have excellent optical, electronic and self-assembly properties, and have important applications in organic light-emitting diodes (OLED), organic field effect transistors (OFET), organic solar photovoltaic cells (OPVC) and other fields. The introduction of heteroatoms to PAHs can adjust the electronic structure, dipole moment, and the self-assembly behavior. Among them, sulfur-doped PAHs have been widely studied. Due to the proper energy level and bonding mode of sulfur atom, the sulfur-doped PAHs have stronger dipole-dipole interactions, electron donating ability, and weakened aromaticity. Sulfur-doped PAHs usually exhibit unique redox characteristics and better hole transporting, so they are widely used as p-type organic semiconductor and electronic donor in photoelectric conversion, and donation unit in donor-acceptor conjugated molecules. Doping PAHs with sulfur is mainly through two ways: post-modification and fusing the sulfur-containing heterocyclic unit. On the other hand, regarding the regulation of geometric structure of carbon skeleton, non-hexagonal ring is introduced to transform the molecular structure from planar to curved structure. The structural distortion can be achieved by the peripherial stereo-hindrance. For example, the PAHs containing helicene units have a highly distorted structure, thus showing a unique optical, electric and assembly properties. In order to construct novel PAHs, this article combines heteroatom doping and geometric control of carbon skeleton. A twisted tri-sulfur-doped PAH C36S3H10(C9H11)6 (molecule 1 ) was synthesized by oxidative cyclodehydrogenation of an oligophenylene precursor, which contains three thiophene rings. X-ray single crystal diffraction exactly characterized the structure of molecule 1 . Because the ring is not completely fused, molecule 1 contains two [5]helicene units, which leads to a twisted molecular structure. In crystalline state, molecule 1 forms dimers through C−H···π and weak π-π interactions, which further packs into one-dimensional columnar stacking through the weak interactions of C−H···π and C−H···S. Different from the planar PAHs, the twisted molecule 1 is not easy to aggregate in solution. Molecule 1 exhibits a yellow photoluminescence, but its quantum yield is low. Combined with the study of transient fluorescence spectroscopy, it is speculated that its twisted molecular structure may be the reason for its low quantum yield. The synthesis of molecule 1 enriches the family of sulfur-doped PAHs, and the derivatives with alkyl chains of molecule 1 can be synthesized in the future and be used as organic semiconductors or electron donors in solar cells and organic electronic devices, etc.

Study of refolding of a denatured protein and microenvironment probed through FRET to a twisted intramolecular charge transfer fluorescent biosensor molecule

In the present study, Fӧrster Resonance Energy Transfer (FRET) from Tryptophan residues (Trp) of bovine serum albumin (BSA) to a nongenotoxic and nontoxic molecule, trans-2-[4-(dimethylamino)styryl]benzothiazole (DMASBT) resulting in fluorescence from the twisted intramolecular charge transfer (TICT) state of the latter has been explored to probe the gemini surfactant induced unfolding and β-cyclodextrin (β-CD) induced refolding of the protein. DMASBT as a potential acceptor in FRET process with its polarity-sensitive TICT fluorescence properties is found to be an efficient biosensor molecule to mark the changes in microenvironment as well as conformations of the protein. λmax of TICT fluorescence band of DMASBT in native protein at 486 nm is red-shifted to 503 nm in unfolded protein which is blue-shifted to 487 nm upon refolding of the protein. Process of BSA fluorescence quenching through FRET to DMASBT has been utilized to compare between the hydrophobic area and fractional accessibility to quencher in native and refolded protein. Fluorescence quenching data have also been used to explain the binding affinity of DMASBT with native, refolded and unfolded BSA. Study reveals the roles of spacer group of gemini surfactants, 12-4-12,2Br− and 12-8-12,2Br− on refolding and unfolding of BSA. A gemini surfactant with a longer spacer is found to be easily stripped off by β-CD resulting in better refolding of protein gaining a larger hydrophobic area. Results obtained corroborate well with the findings from other experimental measurements on circular dichroism, dynamic light scattering and Hg2+ ion-induced fluorescence quenching. An easy and efficient method to study the microenvironment, and unfolding and refolding of a protein is presented here.

Mechanics of Twisted DNA Molecule Adsorbed on a Biological Membrane

DNA is the carrier of all cellular genetic information and increasingly used in nanotechnology. The study of DNA molecule achieved in vitro while submitting the DNA to all chemicals agent capabilities to destabilize links hydrogen, such as pH, temperature. In fact, the DNA enveloped in the membrane cellular, so it is legitimate to study the influence of membrane undulations. In this work, we try to show that the fluctuations of the membrane can be considerate as a physics agent is also capable to destabilize links hydrogen. In this investigation, we assume that each pair base formed an angle an with the membrane’s surface. We have proposed a theoretical model, and we have established a relationship between the angle formed by the pair base θeq and an angle formed by the membrane and each pair base. We assume that DNA and biomembrane interact via a realistic potential of Morse type. To this end, use is made of a generalized model that extends that introduced by M. Peyrard and A. R. Bishop in the past modified by M. Zoli. This generalized model is based on the resolution of a Schrodinger-like equation. The exact resolution gives the expression of the ground state, and the associated eigenvalue (energy) that equals the free energy, in the thermodynamic limit. First, we compute the denaturation temperature of DNA strands critical temperature. Second, we deduce all critical properties that mainly depend on the parameters of the model, and we quantify the effects of the membrane undulations. These undulations renormalize all physical quantities, such as harmonic stacking, melting temperature, eigenfunctions, eigenvalues and regular part of specific heat.

Rational Design of Dual-State Emission Luminogens with Solvatochromism by Combining a Partially Shared Donor-Acceptor Pattern and Twisted Structures.

We report a general design strategy for a new class of luminogens with dual-state emission (DSEgens) that are brightly emissive in both the solution and solid state, with solvatochromism properties, by constructing a partially shared donor-acceptor pattern based on a twisted molecule. The DSEgens with bright fluorescence emission in both the solid and solution state demonstrate a unique solvatochromism behaviour depending on solvent polarity and thus may have applications in anti-counterfeiting.

A dopant-free twisted organic small-molecule hole transport material for inverted planar perovskite solar cells with enhanced efficiency and operational stability

Low-cost solution-processable inverted perovskite solar cells (PSCs) demonstrate great potential toward future photovoltaic market. Unfortunately, general hole transport materials (HTMs) within inverted structure make the performance and stability far uncompetitive compared to the normal structure. Interrogating the fundamentals of these materials, moderate charge carrier mobility and susceptible environmental stability of the undoped molecules are the main causes. Herein, a twisted molecule XY1 is developed as a potential robust dopant-free HTM for inverted PSCs. Compared with traditional poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), XY1 exhibits much higher hole transport ability and peculiar ultraviolet absorption. Hysteresis-free inverted PSCs based on XY1 exhibits the power conversion efficiency (PCE) of 18.78%, which is among the highest values for inverted PSCs based on dopant-free HTMs. After light soaking for 200 h, the original PCE of XY1-based device is still maintained at the 95% level, indicating the substantially improved operational stability. Besides, large-area (1.00 cm2) inverted PSC based on XY1 shows a competitive PCE of 17.82%.

Fluorescence Resonance Energy Transfer, Small-Angle Neutron Scattering, and Dynamic Light Scattering Study on Interactions of Gemini Surfactants Having Different Spacer Groups with Protein at Various Regions of Binding Isotherms.

The binding interactions of three gemini surfactants having different spacer groups (12-4-12, 12-8-12, and 12-4(OH)-12) with a high concentration (150 μM) of bovine serum albumin (BSA) at various regions of binding isotherms have been studied by means of steady-state fluorescence and fluorescence anisotropy, time-correlated single-photon counting fluorescence of trans-2-[4-(dimethylamino)styryl]benzothiazole, small-angle neutron scattering (SANS), and dynamic light scattering (DLS) measurements. The fluorescence resonance energy transfer phenomenon between the twisted intramolecular charge transfer fluorescent molecule, trans-2-[4-(dimethylamino)styryl]benzothiazole as an acceptor, and tryptophan 213 (Trp-213) of BSA as a donor has been successfully used to probe the binding interactions of gemini surfactants with protein at all regions of binding isotherms. The increasing order of energy transfer efficiency at a higher concentration range of surfactants is 12-8-12 > 12-4-12 > 12-4(OH)-12. Stronger binding of micelles of gemini surfactant molecules having a comparatively more hydrophobic spacer group with the hydrophobic segments of the protein results in closer approach of trans-2-[4-(dimethylamino)styryl]benzothiazole molecules solubilized in micelles to Trp-213. The average excited-state lifetimes become shorter with a trend of increase in contribution from the fast component and decrease in contribution from the slow component to the decay with increasing concentration of a surfactant. The nonradiative rate constant of trans-2-[4-(dimethylamino)styryl]benzothiazole increases with increasing concentration of a surfactant because the average microenvironment around it in protein–surfactant aggregates is more polar as compared to that in native protein. SANS and DLS measurements were carried out for the study of the structural deformations in the protein, on enhancement of the concentration of the gemini surfactants. The necklace and bead model has been used for the analysis of SANS data for the protein–surfactant complexes. At a higher concentration range, 12-8-12 and 12-4-12 have a slightly smaller fractal dimension and a larger correlation length as compared to 12-4(OH)-12. DLS data show that the increasing order of hydrodynamic diameter for the complexes of protein with three gemini surfactants in their high concentration range is 12-4(OH)-12 < 12-4-12 < 12-8-12.

4-(4-Acetyl-5-methyl-1H-1,2,3-triazol-1-yl)benzo-nitrile: crystal structure and Hirshfeld surface analysis.

The title compound, C12H10N4O, comprises a central 1,2,3-triazole ring (r.m.s. deviation = 0.0030 Å) flanked by N-bound 4-cyano-phenyl and C-bound acetyl groups, which make dihedral angles of 54.64 (5) and 6.8 (3)° with the five-membered ring, indicating a twisted mol-ecule. In the crystal, the three-dimensional architecture is sustained by carbonyl-C=O⋯π(triazo-yl), cyano-C≡N⋯π(triazo-yl) (these inter-actions are shown to be attractive based on non-covalent inter-action plots) and π-π stacking inter-actions [inter-centroid separation = 3.9242 (9) Å]. An analysis of the Hirshfeld surface shows the important contributions made by H⋯H (35.9%) and N⋯H (26.2%) contacts to the overall surface, as well as notable contributions by O⋯H (9.9%), C⋯H (8.7%), C⋯C (7.3%) and C⋯N (7.2%) contacts.

Concentration-dependent supramolecular patterns of C3 and C2 symmetric molecules at the solid/liquid interface.

Here we report on a scanning tunnelling microscopy (STM) investigation on the self-assembly of C3- and C2-symmetric molecules at the solution/graphite interface. 1,3,5-tris((E)-2-(pyridin-4-yl)vinyl)benzene and 1,1,2,2-tetrakis(4-(pyridin-4-yl)phenyl)ethane are used as model systems. These molecules displayed a concentration dependent self-assembly behaviour on graphite, resulting in highly ordered supramolecular structures, which are stabilized jointly by van der Waals substrate-adsorbate interactions and in-plane intermolecular H-bonding. Denser packing is obtained when applying a relatively high concentration solution to the basal plane of the surface whereas a less dense porous network is observed upon lowering the concentration. We show that the molecular conformation does not influence the stability of the self-assembly and a twisted molecule can pack into dense and porous architectures under the concentration effect.

Charge transport properties of a twisted DNA molecule: A renormalization approach

In this work we study the charge transport properties of a nanodevice consisting of a finite segment of the DNA molecule sandwiched between two metallic electrodes. Our model takes into account a nearest-neighbor tight-binding Hamiltonian considering the nucleobases twist motion, whose solutions make use of a two-steps renormalization process to simplify the algebra, which can be otherwise quite involved. The resulting variations of the charge transport efficiency are analyzed by numerically computing the main features of the electron transmittance spectra as well as their I×V characteristic curves.

Striking effect of intra- versus intermolecular hydrogen bonding on zwitterions: physical and electronic properties.

We report the synthesis, characterization, and application of novel zwitterions. The zwitterionic structures consist of a positively charged cyanine and negatively charged dienolate moieties, confirmed by experimental observations and theoretical calculations. Single crystal X-ray studies revealed that BIT-(NPh)2 is a coplanar molecule that forms 1-D chains via π-π interactions. In contrast, BIT-(NHexyl)2 is a twisted molecule with a dihedral angle of 78° between the charged planes. In charge transport studies, thin films of the flat zwitterion show semiconducting properties, with a hole mobility of 2.1 × 10(-4) cm(2) V(-1) s(-1) while the twisted zwitterion is a high resistivity insulator.

Photochromism change by conformation control in macrocyclic boronic ester cavity

N-salicylideneaniline derivatives are known to show photochromism by UV light, and it depends on the molecular conformation in the crystal. The twisted molecule is photochromic but the planar one is not[1,2]. N-salicylidene-2-aminopyridine (2SAP) always has a planar conformation due to the chemical structure without steric hindrance, therefore 2SAP is known as non-photochromic. However, by confining the molecule in a cavity of the macrocyclic boronic ester 1[3], the conformation and photochromism can be controlled. The inclusion crystal of 1 (homo-parallel form) has a special feature to have a channel type crystal structure in which the macrocyclic ring aligned one-dimensionally to include guest molecules. Interestingly, the crystals can reversibly absorb/desorb guests maintaining the crystal structure, because the channel structure is robust. To exchange the included guests, the crystal of 1(homo-parallel form) was immersed in the melt of 2SAP at 90°C. The obtained inclusion crystal showed photochromism. In the crystal structure, the shape of residual electron density for 2SAP indicated the conformation of 2SAP was twisted due to the confining in the cavity, which is the reason for photochromism. On the other hand, the recrystallization of 1 and 2SAP from THF / hexane solution unexpectedly gave hetero-antiparallel form of 1 because of the dynamic covalent bond formation in the boronic esters (Fig.). As this hetero-antiparallel form has planar cavity in the molecule, the conformation of the included guest molecule, 2SAP, is also planar as always seen. Therefore the inclusion crystal is non-photochromic. Thus, photochromism change of 2SAP was realized by conformational control through confining in the cavity of macrocyclic boronic ester.

Anion and Solvent Induced Chirality Inversion in Macrocyclic Lanthanide Complexes

A series of the lanthanide(III) or yttrium(III) complexes of the type [LnL(NO3)(H2O)2](NO3)2, [LnL(NO3)(H2O)](NO3)2, [LnL(H2O)2](NO3)3, and [LnLCl(H2O)2]Cl2 where L is an all-R or all-S enantiomer (L(R) or L(S)) of the chiral hexaaza macrocycle, 2(R),7(R),18(R),23(R)- or 2(S),7(S),18(S),23(S)-1,8,15,17,24,31-hexaazatricyclo[25.3.1.1.0.0]-dotriaconta-10,12,14,26,28,30-hexaene, and Ln(III) = Sm(III), Tb(III), Ho(III), Er(III), Tm(III), Yb(III), Lu(III), or Y(III), have been synthesized and structurally characterized. The crystal structure of the free macrocycle shows a highly twisted molecule, preorganized for the formation of helical complexes. The crystal structures of the lanthanide(III) complexes show two different diastereomeric forms of the macrocycle with different configurations at the stereogenic amine nitrogen atoms: (RRRR) or (RSRS) (denoted as L(RI) and L(RII), respectively). The L(RI) diastereomeric form of the nitrate derivatives [LnL(NO3)(H2O)](NO3)2 (Ln = Ho, Er) and [LnL(H2O)2](NO3)3 (Ln = Tm, Yb, Lu) convert slowly to the L(RII) form in methanol or acetonitrile solutions, while this process is not observed for the L(RI) diastereomers of analogous chloride derivatives [LnL(H2O)2]Cl3 (Ln = Tm, Yb, Lu). On the other hand, the L(RI) → L(RII) conversion for these Tm(III), Yb(III), and Lu(III) chloride derivatives can be triggered by the addition of external nitrate anions. The circular dichroism (CD) and (1)H NMR data indicate initial fast exchange of axial chloride for axial nitrate ligand, followed by slow chirality inversion of the equatorial macrocyclic ligand.

The Marriage of Peripherally Metallated and Directly Linked Porphyrins: Bromidobis(phosphine)platinum(II) as a Cation‐Stabilizing Substituent on Directly Linked and Fused Triply Linked Diporphyrins

A meso-bromidoplatiniobis(triphenylphosphine) η(1)-organometallic porphyrin monomer was prepared by the oxidative addition of meso-bromoZnDPP (DPP=dianion of 5,15-diphenylporphyrin) to a platinum(0) species. The meso-meso directly linked dimeric porphyrin (5) was prepared from this monomer by silver(I)-promoted oxidative coupling and planarized to give a triply linked dizinc(II) porphyrin dimer (8). Acidic demetallation of 8 afforded the bis(free base) 9. Dimer 5 was demetallated then remetallated with nickel(II) to give the dinickel(II) analogue 10, the X-ray crystal structure of which showed a twisted molecule with ruffled, orthogonal NiDPP rings, terminated by square-planar trans-[Pt(PPh3)2Br] units. New compounds were fully characterized spectroscopically, and the fused diporphyrin exhibited a broad, low-energy, near-IR electronic absorption band near 1100 nm. Electrochemical measurements of this series indicate that the organometallic fragment is a strong electron donor towards the porphyrin ring. The triply linked organometallic diporphyrin has a substantially lowered first one-electron oxidation potential (-0.35 V versus the ferrocene/ferrocenium couple (Fc/Fc(+))) and a narrow HOMO-LUMO gap of 0.96 V. Solutions prepared for NMR spectroscopy slowly decompose with degradation of the signals, which is attributed to partial oxidation to the cation radical. This paramagnetic species can be reduced in situ by hydrazine to restore the NMR spectrum to its former appearance. The combined influence of the two [Pt(PPh3)2Br] electron-donating substituents is sufficient to make dimer too aerobically unstable to allow further elaboration.

Single-crystal Field-effect Transistors with a Furan-containing Organic Semiconductor Having a Twisted π-Electronic System

Abstract We focus on aggregated structures and charge-transporting properties in semiconductor assemblies of a new-type twisted π-conjugated molecule, dinaphtho[2,1-b:1′,2′-d]furan (DNF-U). Single crystals were successfully grown by physical vapor transport to form a two-dimensional herringbone packing structure, which is advantageous for intermolecular charge transport. Based on the packing structure, relatively large transfer integrals were theoretically calculated to be 20 and 57 meV for C–H···π and π···π direction, respectively. The single-crystal field-effect transistors exhibited notable hole mobility of up to 1.0 cm2 V−1 s−1.