Intermolecular interactions in pi-stacked conjugated molecules. Synthesis, structure, and spectral characterization of alkyl bithiazole oligomers

Tuning the thermostability of GHG gels by salts at different positions on the Hofmeister scale

The influence of Hofmeister cations (NH4+, Na+, Mg2+) and anions (H2PO4-, CH3COO-, Cl-, NO3-) on the thermostability of a GHG hydrogel was investigated. The combined results of UV circular dichroism (UVCD) and Small Amplitude Oscillatory Shear Rheology experiments reveal that the addition of salt reduces the stability of the gel phase and the underlying fibrils. In line with the cationic Hofmeister hierarchy, the chaotropic Mg2+ ions caused the greatest thermal destabilization of the gel phase with the gel → sol transition temperature Tgs value lowered by 10 °C. In the absence of salt, the gel → sol transition probed by the storage modulus and microscopy is biphasic. In the presence of salt, it becomes monophasic. Contrary to expectations the presence of Hofmeister anions leads to a nearly identical reduction of the gel → sol transition temperatures. However, UVCD spectra suggest that they affect the ππ-stacking between imidazole groups to a different extent. We relate the absence of ion specificity regarding the solubility of fibrils (probed by UVCD) to the observed enthalpy-entropy compensation of the dissolution process. Our results combined show how CD spectroscopy and rheology combined yields a more nuanced picture of the processes underlying the gel → sol transition.

Unraveling the Structure-Property-Performance Relationships of Fused-Ring Nonfullerene Acceptors: Toward a C-Shaped ortho-Benzodipyrrole-Based Acceptor for Highly Efficient Organic Photovoltaics

The high-performance Y6-based nonfullerene acceptors (NFAs) feature a C-shaped A-DA'D-A-type molecular architecture with a central electron-deficient thiadiazole (Tz) A' unit. In this work, we designed and synthesized a new A-D-A-type NFA, termed CB16, having a C-shaped ortho-benzodipyrrole-based skeleton of Y6 but with the Tz unit eliminated. When processed with nonhalogenated xylene without using any additives, the binary PM6:CB16 devices display a remarkable power conversion efficiency (PCE) of 18.32% with a high open-circuit voltage (Voc) of 0.92 V, surpassing the performance of the corresponding Y6-based devices. In contrast, similarly synthesized SB16, featuring an S-shaped para-benzodipyrrole-based skeleton, yields a low PCE of 0.15% due to the strong side-chain aggregation of SB16. The C-shaped A-DNBND-A skeleton in CB16 and the Y6-series NFAs constitutes the essential structural foundation for achieving exceptional device performance. The central Tz moiety or other A' units can be employed to finely adjust intermolecular interactions. The single-crystal X-ray structure reveals that ortho-benzodipyrrole-embedded A-DNBND-A plays an important role in the formation of a 3D elliptical network packing for efficient charge transport. Solution structures of the PM6:NFAs detected by small- and wide-angle X-ray scattering (SWAXS) indicate that removing the Tz unit in the C-shaped skeleton could reduce the self-packing of CB16, thereby enhancing the complexing and networking with PM6 in the spin-coating solution and the subsequent device film. Elucidating the structure-property-performance relationships of A-DA'D-A-type NFAs in this work paves the way for the future development of structurally simplified A-D-A-type NFAs.

A Sequential Transition Metal and Organocatalytic Approach to the Enantioselective Synthesis of C2-Spiroindoline Systems

We report herein an organocatalyzed enantioselective spirocyclization strategy to access valuable C2-spiroindoline scaffolds bearing a quaternary stereocenter via an aza-Michael addition reaction, wherein the acid additive plays the role of dual functionality. The substrates for this key step were put together by an exo-selective, Pd-catalyzed γ-arylation of silyldienol ethers of the corresponding cyclohexenones. A close alliance between a low catalyst loading and a slow reaction rate yields C2-spiroindolines with good enantioselectivity.

Memory Effect by Melt Crystallization Observed in Polymorphs of a Benzothieno-Benzothiophene Derivative

This work provides a comprehensive illustration of a crystalline melt memory effect recorded for three solvates of the 2,7-bis(2-(2-methoxyethoxy)ethoxy)benzo[b]benzo[4,5] thieno[2,3-d]thiophene (OEG-BTBT) molecule with dichloromethane (DCM) molecules. Combined optical microscopy and X-ray diffraction measurements at different temperatures are used to get an overview of the structural and morphological properties like melting points, isotropic transition temperatures, induction times, and crystallization kinetics of the three forms. An outstanding observation is made upon annealing the three polymorphs at temperatures well above their respective melting points as well as above the optical clearance temperature. After cooling back to room temperature, recrystallization results in the formation of the initial phase present before the annealing process. This melt memory effect is observed for all three solvates. These observations can be correlated to the strong interaction between the DCM molecules and the oligoethylene glycol side chains, even in the molten state. This conclusion rationalizes the experimental observation made upon solvent vapor annealing of the crystalline sample with DCM, which unambiguously transformed the system into a disordered state.

Tuning sterol extraction kinetics yields a renal-sparing polyene antifungal

Decades of previous efforts to develop renal-sparing polyene antifungals were misguided by the classic membrane permeabilization model1. Recently, the clinically vital but also highly renal-toxic small-molecule natural product amphotericin B was instead found to kill fungi primarily by forming extramembraneous sponge-like aggregates that extract ergosterol from lipid bilayers2-6. Here we show that rapid and selective extraction of fungal ergosterol can yield potent and renal-sparing polyene antifungals. Cholesterol extraction was found to drive the toxicity of amphotericin B to human renal cells. Our examination of high-resolution structures of amphotericin B sponges in sterol-free and sterol-bound states guided us to a promising structural derivative that does not bind cholesterol and is thus renal sparing. This derivative was also less potent because it extracts ergosterol more slowly. Selective acceleration of ergosterol extraction with a second structural modification yielded a new polyene, AM-2-19, that is renal sparing in mice and primary human renal cells, potent against hundreds of pathogenic fungal strains, resistance evasive following serial passage in vitro and highly efficacious in animal models of invasive fungal infections. Thus, rational tuning of the dynamics of interactions between small molecules may lead to better treatments for fungal infections that still kill millions of people annually7,8 and potentially other resistance-evasive antimicrobials, including those that have recently been shown to operate through supramolecular structures that target specific lipids9.

Polymeric Phthalocyanine-Based Nanosensitizers for Enhanced Photodynamic and Sonodynamic Therapies

Photodynamic therapy and sonodynamic therapy are two highly promising modalities for cancer treatment. The latter holds an additional advantage in deep-tumor therapy owing to the deep penetration of the ultrasonic radiation. The therapeutic efficacy depends highly on the photo/ultrasound-responsive properties of the sensitizers as well as their tumor-localization property and pharmacokinetics. A novel nanosensitizer system based on a polymeric phthalocyanine (pPC-TK) is reported herein in which the phthalocyanine units are connected with cleavable thioketal linkers. Such polymer could self-assemble in water forming nanoparticles with a hydrodynamic diameter of 48 nm. The degradable and flexible thioketal linkers could effectively inhibit the π-π stacking of the phthalocyanine units, rendering the resulting nanoparticles an efficient generator of reactive oxygen species upon light or ultrasonic irradiation. The nanosensitizer could be internalized into cancer cells readily, inducing cell death by efficient photodynamic and sonodynamic effects. The potency is significantly higher than that of the monomeric phthalocyanine (PC-4COOH). The nanosensitizer could also effectively inhibit the growth of tumor in liver tumor-bearing mice by these two therapies without causing noticeable side effects. More importantly, it could also retard the growth of a deep-located orthotopic liver tumor in vivo by sonodynamic therapy.

Sequence-Specific Dual DNA Binding Modes and Cytotoxicities of N-6-Functionalized Norcryptotackieine Alkaloids

Norcryptotackieine (1a) belongs to the indoloquinoline class of alkaloids isolated from Cryptolepis sanguinolenta, a plant species that has been traditionally used as an antimalarial agent. Additional structural modifications of 1a can potentially enhance its therapeutic potency. Indoloquinolines such as cryptolepine, neocryptolepine, isocryptolepine, and neoisocryptolepine show restricted clinical applications owing to their cytotoxicity deriving from interactions with DNA. Here, we examined the effect of substitutions at the N-6 position of norcryptotackieine on the cytotoxicity, as well as structure-activity relationship studies pertaining to sequence specific DNA-binding affinities. The representative compound 6d binds DNA in a nonintercalative/pseudointercalative fashion, in addition to nonspecific stacking on DNA, in a sequence selective manner. The DNA-binding studies clearly establish the mechanism of DNA binding by N-6-substituted norcryptotackieines and neocryptolepine. The synthesized norcryptotackieines 6c,d and known indoloquinolines were screened on different cell lines (HEK293, OVCAR3, SKOV3, B16F10, and HeLa) to assess their cytotoxicity. Norcryptotackieine 6d (IC50 value of 3.1 μM) showed 2-fold less potency when compared to the natural indoloquinoline cryptolepine 1c (IC50 value of 1.64 μM) in OVCAR3 (ovarian adenocarcinoma) cell lines.

The influence of molecular design on structure-property relationships of a supramolecular polymer prodrug

Supramolecular self-assemblies of hydrophilic macromolecules functionalized with hydrophobic, structure-directing components have long been used for drug delivery. In these systems, loading of poorly soluble compounds is typically achieved through physical encapsulation during or after formation of the supramolecular assembly, resulting in low encapsulation efficiencies and limited control over release kinetics, which are predominately governed by diffusion and carrier degradation. To overcome these limitations, amphiphilic prodrugs that leverage a hydrophobic drug as both the therapeutic and structure-directing component can be used to create supramolecular materials with higher loading and controlled-release kinetics using biodegradable or enzymatically cleavable linkers. Here, we report the design, synthesis, and characterization of a library of supramolecular polymer prodrugs based on poly(ethylene glycol) (PEG) and the proregenerative drug 1,4-dihydrophenonthrolin-4-one-3-carboxylic acid (DPCA). Structure-property relationships were elucidated through experimental characterization of prodrug behavior in both the wet and dry states using scattering techniques and electron microscopy and corroborated by coarse-grained modeling. Molecular architecture and the hydrophobic-to-hydrophilic ratio of PEG-DPCA conjugates strongly influenced their physical state in water, ranging from fully soluble to supramolecular spherical assemblies and nanofibers. Molecular design and supramolecular structure, in turn, were shown to dramatically alter hydrolytic and enzymatic release and cellular transport of DPCA. In addition to potentially expanding therapeutic options for DPCA through control of supramolecular assemblies, the design principles elaborated here may inform the development of other supramolecular prodrugs based on hydrophobic small-molecule compounds.

Topology-Controlled AIEE of Iminocoumarin Luminophores

Aggregation-induced emission enhancement (AIEE) is an unusual phenomenon where luminophores show a higher photoluminescence efficiency in the aggregated and solid state. We report the design and synthesis of a series of luminophores 1-4 with imine functionality at 6 position of coumarin and studied their AIE propensities on self-assembly. The effect of the topology of the phenolic hydroxyl group on the emission behaviour of the luminophores has been investigated. The imines show significant solvatochromism with high emission in non-polar solvents, whereas the emission gets quenched in the polar solvent. The fluorescence in the toluene-hexane mixture arises due to the aggregation of fluorophores and falls under the category of AIEE. Not only the solution state emission of the isomeric iminocoumarin luminophores is notably varied, but also their solid-state emission found to be significantly different from each other. Moreover, the iminocoumarin 1 selectively recognizes Fe(III) over Fe(II) with a prominent color change. In situ oxidation of Fe(II) with H₂ O₂ exhibits the same effect like Fe(III) and developed a chemical combinational logic gate.

Highly Sensitive Ultrastable Electrochemical Sensor Enabled by Proton-Coupled Electron Transfer

Electrochemical sensors are critical to artificial intelligence by virtue of capability of mimicking human skin to report sensing signals. But their practical applications are restricted by low sensitivity and limited cycling stability, which result from piezoionic mechanism with insufficient sensing response. Here, we report a highly sensitive ultrastable sensor based on proton-coupled electron transfer, which is different from piezoionic mechanism. The sensor gives a high sensing signal output of 117 mV, which is 16 times higher than that of counterpart device (7 mV). It delivers excellent working stability with performance retention as high as 99.13% over 10 000 bending cycles in air, exceeding that of the best-known sensors reported previously. The flexible sensor displays high sensitivity in detecting real-time signals of human activities with large and subtle deformations, including wrist bending, moving speed, pulse wave and voice vibration. Smart functions, such as braille language and handwriting recognitions, are demonstrated for artificial intelligence.

Benzo/Naphthodifuranone-Based Polymers: Effect of Perpendicular-Extended Main Chain π-Conjugation on Organic Field-Effect Transistor Performances

For polymer semiconductors, the backbone structure plays an essential role in determining their physicochemical properties and charge transport behaviors. In this work, two donor-acceptor-type polymers (P-BDF and P-NDF) based on benzodifuranone (BDF) and naphthodifunarone (NDF) as electron-deficient moieties and indaceno-dithiophene as electron-rich groups are designed, synthesized and, for the first time, applied in organic field-effect transistor. P-BDF and P-NDF differ from their backbone structures while P-BDF has a more planar backbone conformation due to its smaller conjugated core size and P-NDF features a perpendicular-extended main chain structure. As a result, P-BDF polymer exhibits bathochromic optical absorption, deeper molecular orbital energy levels, and more importantly, closer π-stacking and stronger aggregation in the solid state and thus affords a more promising hole mobility of up to 0.85 cm² V^-1 s^-1 in OFET devices, while that of the P-NDF-based devices is only 0.55 cm² V^-1 s^-1 . The results suggest the great potential of BDF/NDF-type chromophores in constructing novel organic semiconductors and also indicate that the main chain coplanarity of polymer semiconductors is more essential than the sole extension of π-conjugations (especially at the perpendicular direction of polymer main chains) for the design of high-performance OFET materials.

Efficient energy transfer mitigates parasitic light absorption in molecular charge-extraction layers for perovskite solar cells

Organic semiconductors are commonly used as charge-extraction layers in metal-halide perovskite solar cells. However, parasitic light absorption in the sun-facing front molecular layer, through which sun light must propagate before reaching the perovskite layer, may lower the power conversion efficiency of such devices. Here, we show that such losses may be eliminated through efficient excitation energy transfer from a photoexcited polymer layer to the underlying perovskite. Experimentally observed energy transfer between a range of different polymer films and a methylammonium lead iodide perovskite layer was used as basis for modelling the efficacy of the mechanism as a function of layer thickness, photoluminescence quantum efficiency and absorption coefficient of the organic polymer film. Our findings reveal that efficient energy transfer can be achieved for thin (≤10 nm) organic charge-extraction layers exhibiting high photoluminescence quantum efficiency. We further explore how the morphology of such thin polymer layers may be affected by interface formation with the perovskite.

Dependence of the performance of light-emitting diodes on the molecular weight of the electroluminescent polymer PFO-MEH-PPV

Controlled synthesis of the electroluminescent polymer PFO-MEH-PPV (poly[(9,9-dioctyl-2,7-divinylenefluorenylene)-alt-co-(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene)]) provided samples of varying molecular weight (Mw) in the range 20–360 kDa, as determined by gel-permeation chromatography and light scattering. The samples were used as the active layers in organic light-emitting diodes (OLEDs), and the performance of the devices was examined as a function of Mw. Turn-on voltages fell in the range 1.92–2.78 V, luminances varied from 231 to 5826 cd/m2, and luminous efficacies ranged from 0.06 to 0.90 lm/W. The emitted colour was found to vary from green to yellow as Mw increases. Optimal performance was attained by using PFO-MEH-PPV with Mw = 100 kDa. To help reveal how Mw determines the performance of OLEDs, relative quantum yields of photoluminescence in solutions and films were measured, and films were characterized by atomic force microscopy and transmission electron microscopy.

Benzosiloles with Crystallization-Induced Emission Enhancement of Electrochemiluminescence: Synthesis, Electrochemistry, and Crystallography

Crystallization-induced emission enhancement (CIEE) was demonstrated for the first time for electrochemilunimescence (ECL) with two new benzosiloles. Compared with their solution, the films of the two benzosiloles gave CIEE of 24 and 16 times. The mechanism of the CIEE-ECL was examined by spooling ECL spectroscopy, X-ray crystal structure analysis, photoluminescence, and DFT calculations. This CIEE-ECL system is a complement to the well-established aggregation-induced emission enhancement (AIEE) systems. Unique intermolecular interactions are noted in the crystalline chromophore. The first heterogeneous ECL system is established for organic compounds with highly hydrophobic properties.

Arginine-Induced Self-Assembly of Protoporphyrin to Obtain Effective Photocatalysts in Aqueous Media Under Visible Light

The fabrication of controlled supramolecular nanostructures via self-assembly of protoporphyrin IX (PPIX) was studied with enantiomerically pure l-arginine and d-arginine, and we have shown that stoichiometry controlled the morphology formed. The nanostructure morphology was mainly influenced by the delicate balance of π-π stacking interactions between PPIX cores, as well as H-bonding between the deprotonated acidic head group of PPIX with the guanidine head group of arginine. PPIX self-assembled with l-/d-arginine to create rose-like nanoflower structures for four equivalents of arginine that were 5–10 μm in length and 1–4 μm diameter. We employed UV-vis, fluorescence spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), dynamic light scattering (DLS) and Fourier transform infrared spectroscopy (FT-IR) techniques to characterize the resulting self-assembled nanostructures. Furthermore, we investigated the catalytic activity of PPIX and arginine co-assembled materials. The fabricated PPIX–arginine nanostructure showed high enhancement of photocatalytic activity through degradation of rhodamine B (RhB) with a decrease in dye concentration of around 78–80% under simulated visible radiation.

Unprecedented Centimeter-Long Carbon Nitride Needles: Synthesis, Characterization and Applications

Free standing centimeter-long 1D nanostructures are highly attractive for electronic and optoelectronic devices due to their unique photophysical and electrical properties. Here a simple, large-scale synthesis of centimeter-long 1D carbon nitride (CN) needles with tunable photophysical, electric, and catalytic properties is reported. Successful growth of ultralong needles is acquired by the utilization of 1D organic crystal precursors comprised of CN monomers as reactants. Upon calcination at high temperatures, the shape of the starting crystal is fully preserved while the CN composition and porosity, and optical and electrical properties can be easily tuned by tailoring the starting elements ratio and final calcination temperature. The facile manipulation and visualization of the CN needles endow their direct electrical measurements by placing them between two conductive probes. Moreover, the CN needles exhibit good photocatalytic activity for hydrogen production owing to their improved light harvesting properties, high surface area, and advantageous energy bands position. The new growth strategy developed here may open opportunities for a rational design of CN and other metal-free materials with controllable directionality and tunable photophysical and electronic properties, toward their utilization in (photo)electronic devices.

Substituent Effects That Control Conjugated Oligomer Conformation through Non-covalent Interactions

Although understanding the conformations and arrangements of conjugated materials as solids is key to their prospective applications, predictive power over these structural factors remains elusive. In this work, substituent effects tune non-covalent interactions between side-chain fluorinated benzyl esters and main-chain terminal arenes, in turn controlling the conformations and interchromophore aggregation of three-ring phenylene-ethynylenes (PEs). Cofacial fluoroarene-arene (ArF-ArH) interactions cause twisting in the PE backbone, interrupting intramolecular conjugation as well as blocking chromophore aggregation, both of which prevent the typically observed bathochromic shift observed upon transitioning PEs from solution to solid. This work highlights two structural factors that determine whether the ArF-ArH interactions, and the resulting twisted, unaggregated chromophores, occur in these solids: (i) the electron-releasing characteristic of substituents on ArH, with more electron-releasing character favoring ArF-ArH interactions, and (ii) the fluorination pattern of the ArF ring, with 2,3,4,5,6-pentafluorophenyl favoring ArF-ArH interactions over 2,4,6-trifluorophenyl. These trends indicate that considerations of electrostatic complementarity, whether through a polar-π or substituent-substituent mechanism, can serve as an effective design principle in controlling the interaction strengths, and therefore the optoelectronic properties, of these molecules as solids.

Enhancing the power conversion efficiency of dye-sensitized solar cells via molecular plasmon-like excitations

We introduce a tactic for employing molecular plasmon-like excitations to enhance solar-to-electric power conversion efficiency of dye-sensitized solar cells. We offer general design principles of dimeric dyes, in which a strong plasmonic interaction between two π-conjugated moieties is promoted. The π-stacked conformations of these dimeric dyes result in a desirable broadened absorption and a longer absorption onset wavelength.

Tuning the structures and photophysical properties of 9,10-distyrylanthrance (DSA) via fluorine substitution

Because of the differences in the position and degree of fluorine substitution, four fluorinated DSA derivatives, namely 4-BFSA, 3-BFSA, BDFSA and BTFSA, display different crystal packing and photophysical properties in the solid state.

Selenium-Containing Fused Bicyclic Heterocycle Diselenolodiselenole: Field Effect Transistor Study and Structure-Property Relationship

The first application of the diselenolodiselenole (C4Se4) heterocycle as an active organic field effect transistor materials is demonstrated here. C4Se4 derivatives (2a-2d) were obtained by using a newly developed straightforward diselenocyclization protocol, which includes the reaction of diynes with selenium powder at elevated temperature. C4Se4 derivatives exhibit strong donor characteristics and planar structure (except 2d). The atomic force microscopic analysis and thin-film X-ray diffraction pattern of compounds 2a-2d indicated the formation of distinct crystalline films that contain large domains. A scanning electron microscopy study of compound 2b showed development of symmetrical grains with an average diameter of 150 nm. Interestingly, 2b exhibited superior hole mobility, approaching 0.027 cm(2) V(-1) s(-1) with a transconductance of 9.2 μS. This study correlate the effect of π-stacking, Se···Se intermolecular interaction, and planarity with the charge transport properties and performance in the field effect transistor devices. We have shown that the planarity in C4Se4 derivatives was achieved by varying the end groups attached to the C4Se4 core. In turn, optoelectronic properties can also be tuned for all these derivatives by end-group variation.

A pillar[5]arene-based [2]rotaxane lights up mitochondria

Subcellular organelle-specific reagents for simultaneous targeting, imaging and treatment are highly desirable for cancer therapy. However, it remains a challenge to fabricate a single molecular platform containing a targeting group, imaging and therapeutic agents through traditional synthesis. Due to their superior sensitivity and photostability, fluorescent probes with aggregation-induced emission (AIE) characteristics have attracted more and more attention in studying the process of translocation, drug release, and excretion of nanomedicines in vitro or in vivo. We construct a pillar[5]arene-based [2]rotaxane (R1) by employing tetraphenylethene (TPE) and triphenylphosphonium (TPP) moieties as stoppers; the TPE unit retains the aggregation-induced emission (AIE) attribute and the TPP group is used as a mitochondria-targeting agent. R1 exhibits enhanced AIE, high specificity to mitochondria, and superior photostability. By introducing doxorubicin (DOX) into R1, prodrug R2 is constructed as a dual-fluorescence-quenched Förster resonance energy transfer (FRET) system, in which the TPE-based axle acts as a donor fluorophore and the DOX unit acts as the acceptor. Upon hydrolysis of R2 in endo/lysosomes, the fluorescences of the carrier and the drug recover. R1 is further utilized as a drug delivery platform to conjugate other anticancer drugs containing amine groups through imine formation to prepare prodrugs. The anticancer drugs are released from these prodrugs in the cells upon hydrolysis of the pH-responsive imine bonds.

A highly-efficient blue-light excitable red phosphor: intramolecular π-stacking interactions in one dinuclear europium(iii) complex

A series of ternary dinuclear europium(iii) complexes [Eu2(2,7-BTFDBC)3-n(DBM)2n(Phen)2] (n = 0, 1, or 2) were synthesized by using 2,7-bis(4'4'4'-trifluoro-1,3-dioxobutyl)-(9-ethyl-9H-carbazole) (2,7-BTFDBC), dibenzoylmethane (DBM), 1,10-phenanthroline (Phen) and europium(iii) ions. All these complexes display a broad excitation band in the blue region and high intensity emission with high colour purity. The intensity of emission significantly increases with the increase of DBM in [Eu2(2,7-BTFDBC)3-n(DBM)2n(Phen)2] (n = 0, 1, or 2). The theoretical predictions of the molecular geometry and electronic absorption spectrum of [Eu2(2,7-BTFDBC)(DBM)4(Phen)2] confirm that the pendant phenyl domains engage in multiple T-shaped and parallel-displaced π-stacking interactions with the coordination sphere of two europium(iii) centers. Using [Eu2(2,7-BTFDBC)(DBM)4(Phen)2] as a red phosphor, a single red LED has been obtained with a ∼460 nm-emitting GaN chip.

Photoluminescent epoxy microspheres: preparation, surface functionalization via grafting polymerization and photophysical properties

Photoluminescent epoxy microspheres with the size of 1–3 μm were prepared. Their surfaces were functionalized with poly(N-vinylpyrrolidone) via RAFT polymerization.

Non-covalent assembly of meso-tetra-4-pyridyl porphine with single-stranded DNA to form nano-sized complexes with hydrophobicity-dependent DNA release and anti-tumor activity

DNA and porphyrin based therapeutics are important for anti-cancer treatment. The present studies demonstrate single-stranded DNA (ssDNA) assembles with meso-tetra-4-pyridyl porphine (MTP) forming porphyrin:DNA nano-complexes (PDN) that are stable in aqueous solution under physiologically relevant conditions and undergo dissociation with DNA release in hydrophobic environments, including cell membranes. PDN formation is DNA-dependent with the ratio of porphyrin:DNA being approximately two DNA nucleobases per porphyrin. PDN produce reactive oxygen species (ROS) in a light-dependent manner under conditions that favor nano-complex dissociation in the presence of hydrophobic solvents. PDN induce light-dependent cytotoxicity in vitro and anti-tumor activity towards bladder cancer xenografts in vivo. Light-dependent, PDN-mediated cell death results from ROS-mediated localized membrane damage due to lipid peroxidation with mass spectrometry indicating the generation of the lipid peroxidation products 9- and 13-hydroxy octadecanoic acid. Our results demonstrate that PDN have properties useful for therapeutic applications, including cancer treatment.

FROM THE CLINICAL EDITOR

In this study, porphyrin-DNA nanocomplexes were investigated as anti-cancer therapeutics inducing ROS production in a light-dependent manner. Efficacy is demonstrated in vitro as well as a in a bladder cancer xenograft model.

H- and J-aggregate behavior in polymeric semiconductors

Aggregates of conjugated polymers exhibit two classes of fundamental electronic interactions: those occurring within a given chain and those occurring between chains. The impact of such excitonic interactions on the photophysics of polymer films can be understood using concepts of J- and H-aggregation originally developed by Kasha and coworkers to treat aggregates of small molecules. In polymer assemblies, intrachain through-bond interactions lead to J-aggregate behavior, whereas interchain Coulombic interactions lead to H-aggregate behavior. The photophysics of common emissive conjugated polymer films are determined by a competition between intrachain, J-favoring interactions and interchain, H-favoring interactions. We review formalisms describing absorption and photoluminescence lineshapes, based on intra- and intermolecular excitonic coupling, electron-vibrational coupling, and correlated energetic disorder. Examples include regioregular polythiophenes, pheneylene-vinylenes, and polydiacetylene.

Solution processable benzooxadiazole and benzothiadiazole based D-A-D molecules with chalcogenophene: field effect transistor study and structure property relationship

We present here the physicochemical characterization of a series of D-A-D type molecules which comprise benzooxadiazole (BDO) and benzothiadiazole (BDT) core symmetrically linked to two aromatic-heterols (furan (F), thiophene (T) and selenophene (Se)) at 4 and 7-positions. The molecular structures of four compounds 2 (T-BDO-T), 3 (Se-BDO-Se), 5 (T-BDT-T), and 6 (Se-BDT-Se) were determined by single-crystal X-ray diffraction. The combination of chalcogen atoms of benzochalcogenadiazole and chalcogenophene in D-A-D molecules has significant impact on their molecular packing in crystal structures. Structural analyses and theoretical calculations showed that all the molecules are nearly planar. Crystal structures of 2, 3, 5, and 6 showed significant short range interactions such as π···π, CH···π, S···π, Se···π, N···H, O···H, S···H, Se···H, S···O, and Se···N interactions, which influence crystal packing and orientation of the capped aromatic-heterol rings with respect to the central BDO or BDT unit. The π-stacking interactions have been observed via intermolecular overlap of the donor with acceptor units of the adjacent molecules which facilitate the charge transport process. Good thermal stability and solubility in common organic solvents make them good candidate for flexible electronics. Interestingly, the molecules 2, 3, and 6 have the propensity to form ordered crystallites when sheared during the drying process in the thin films. Devices based on these solution processable all organic FETs demonstrated hole mobility as high as 0.08 cm(2) V(-1) s(-1) and Ion/Ioff ratio of 10(4).

Effects of stereoisomerism on the crystallization behavior and optoelectrical properties of conjugated molecules

Three stereoisomers of DPP(TBFu)2 are separated and identified to investigate the effects of stereoisomerism on crystal structures and the optoelectrical properties. The crystal structures and FET mobility are sensitive to stereoisomers, in which the mesomer possesses the highest carrier mobility and the greatest crystallization tendency to dominate the crystallization in spin-cast films of the as-synthesized stereoisomeric mixture.

Large electronic bandwidth in solution-processable pyrene crystals: the role of close-packed crystal structure

We examine the interdependence of structural and electronic properties of two substituted pyrene crystals by means of combined spectroscopic probes and density-functional theory calculations. Substituted pyrenes are useful model systems to unravel the interplay of crystal structure and electronic properties in organic semiconductors. To study the effect of steric encumbrance on the crystalline arrangement of two 1,3,6,8-tetraalkynylpyrene derivatives, one features linear n-hexyl side groups while the other contains branched trimethylsilyl groups. Both derivatives form triclinic crystal structures when grown from solution, but the electronic dispersion behavior is significantly different due to differences in π-π overlap along the π-stacking axis. Both systems display dispersion of around 0.45 eV in the valence band, suggesting a high intrinsic hole mobility. However, the direction of the dispersion is different: it is primarily along the π-stacking axis in the trimethylsilyl-substituted derivative, but less aligned with this crystal axis in the hexyl-substituted molecule. This is a direct consequence of the differences in co-facial π electron overlap revealed by the crystallographic studies. We find that photophysical defects, ascribed to excimer-like states, point to the importance of localized trap states.

Controlling growth of molecular crystal aggregates for efficient optical waveguides

Controllable crystal aggregate structures which show highly uniform crystal tubule, rod and cubic like architectures were achieved and the well-defined microrods exhibit outstanding optical waveguide properties.

Role of Molecular Packing in Determining Solid-State Optical Properties of π-Conjugated Materials

The optical properties of π-conjugated organic molecules in their solid state are critically important in determining performance efficiencies of optoelectronic devices such as organic light-emitting diodes and organic thin-film transistors. This Perspective discusses some recent systematic explorations aimed toward arriving at an understanding of the role that molecular packing plays in determining these properties.

(1E,3E)-1,4-Bis(4-methoxyphenyl)buta-1,3-diene

The title compound, C₁₈H₁₈O₂, which exhibits blue emission in the solid state, is an inter­mediate in the preparation of liquid crystals and polymers. The mol­ecule is located on an inversion centre. In the crystal, mol­ecules are arranged in a herringbone motif.