Supramolecular Liquid Crystalline π-Conjugates: The Role of Aromatic π-Stacking and van der Waals Forces on the Molecular Self-Assembly of Oligophenylenevinylenes

Reversible Multilevel Stimuli-Responsiveness and Multicolor Room-Temperature Phosphorescence Emission Based on a Single-Component System

There are limited reports about the transformation of pure organic room-temperature phosphorescence (RTP) materials with multilevel stimuli-responsiveness at different RTP emission wavelengths under external stimuli. It is difficult to ensure efficient intersystem crossing (ISC) in different states of a single-component system. This research reports the conversion of the organic single-component small molecule 1,2-bis(4-alkoxyphenyl)ethane-1,2-dione (N-BOX) with multilevel stimuli-responsiveness between high-efficiency blue and yellow RTP by grinding or thermal annealing N-BOX crystals. The RTP emission of N-BOX in the crystalline state was easy to adjust by external stimuli (grinding or thermal annealing) due to its non-compact packing, which led to a phase transition and generated unique multilevel stimuli-responsiveness. In particular, the RTP quantum yield of 7-BOX with multilevel stimuli-responsiveness reached 68.4 %, which provides an opportunity for regulation of smart optical materials based on pure organic RTP.

Structure of Self-assembled Peptide Determines the Activity of Aggregation-Induced Emission Luminogen-Peptide Conjugate for Detecting Alkaline Phosphatase

The unique property of turning on their fluorescence after aggregation or assembly makes aggregation-induced emission luminogens (AIEgens) ideal luminescent molecules for the construction of self-assembled peptide-based nanoprobes. However, the characteristic highly twisted or propeller-shaped molecular conformation of AIEgens tends to prevent the assembly of AIEgen-peptides. Here, we show that (i) the distance between tetraphenylethene (TPE) and assembled peptides should not be too far (less than five glycines), otherwise the self-assembly of peptides cannot limit the intramolecular rotation of conjugated TPE and the luminous efficiency of TPE-peptide to alkaline phosphatase (ALP) will decrease; (ii) properly increasing the number of amino acids with self-assembly ability (three phenylalanines) can improve their ALP-responsive self-assembly and luminescence ability; (iii) the strategy of co-assembly with a non-AIEgen-capped self-assembled peptide is a simple and effective way to realize the efficient assembly and luminescence of AIEgen-peptides; and (iv) the hydrophilic and hydrophobic balance of the probe should always be considered in the construction of an efficient AIEgen-peptide probe. In addition, AIEgen-peptide probes show good selectivity and sensitivity for ALP detection both in vitro and in live bacteria. These insights illustrated here are crucial for guiding the design of AIEgen-conjugated supramolecular materials, especially for the construction of AIEgen-peptides, for enzymes detection, biomarker imaging, diseases therapy, and other biomedical fields.

Triazole-estradiol analogs: A potential cancer therapeutic targeting ovarian and colorectal cancer

1,2,3-triazoles have continuously shown effectiveness as biologically active systems towards various cancers, and when used in combination with steroid skeletons as a carrier, which can act as a drug delivery system, allows for a creation of a novel set of analogs that may be useful as a pharmacophore leading to a potential treatment option for cancer. A common molecular target for cancer inhibition is that of the Epidermal Growth Factor Receptor/Mitogen Activated Protein Kinase pathways, as inhibition of these proteins is associated with a decrease in cell viability. Estradiol-Triazole analogs were thus designed using a molecular modeling approach. Thirteen of the high scoring analogs were then synthesized and tested in-vitro on an ovarian cancer cell line (A2780) and colorectal cancer cell line (HT-29). The most active compound, Fz25, shows low micromolar activity in both the ovarian (15.29 ± 2.19 µM) and colorectal lines (15.98 ± 0.39 µM). Mechanism of action studies proved that Fz25 moderately arrests cells in the G1 phase of the cell cycle, specifically inhibiting STAT3 in both cell lines. Additionally, Fz57 shows activity in the colorectal line (24.19 ± 1.37 µM). Inhibition studies in both cell lines show inhibition against various proteins in the EGFR pathway, namely EGFR, STAT3, ERK, and mTOR. To further study their effects as therapeutics, Fz25 and Fz57 were studied against drug efflux proteins, which are associated with drug resistance, and were found to inhibit the ABC transporter P-glycoprotein. We can conclude that these estradiol-triazole analogs provide a key for future studies targeting protein inhibition and drug resistance in cancer.

Supramolecular Organogelation Directed by Weak Noncovalent Interactions in Palmitoylated 1,5-Anhydro-d-Glucitol Derivatives

We synthesized a series of novel alicyclic compounds by modifying 1,5-anhydro-d-glucitol with two to four palmitoyl chains, and we explored their self-assembly and gelation behaviors in paraffin. The obtained organogels were studied by field emission scanning electron microscopy, atomic force microscopy, variable-temperature Fourier transform IR spectroscopy, X-ray diffraction analysis, polarized optical microscopy, and transmission spectroscopy. While all the palmitoylated derivatives spontaneously formed fibrous networks and gelated the paraffin, an acetylated derivative of 1,5-anhydro-d-glucitol did not gelatinize the solvent, thus indicating the importance of aliphatic chains for gelation. Interestingly, α- and β- d-glucopyranose with five palmitoyl chains neither gelatinized the solvent nor formed fibrous networks, thus suggesting that the absence of C-1 substitution in 1,5-anhydro-d-glucitol is important for gelation. Fourier transform IR spectroscopy suggested that the formation of weak hydrogen bonds between the carbonyl groups and the C-H groups was the driving force for formation of the supramolecular fibers and for gelation of the solvent.

Synthesis, characterization and crystal structures of novel fluorinated di(thiazolyl)benzene derivatives

A series of 11 novel fluorinated and non-fluorinated di(thiazolyl)benzenes have been synthesized via microwave assisted Stille coupling and characterized using X-ray crystallography.

Flexible and Compressible PEDOT:PSS@Melamine Conductive Sponge Prepared via One-Step Dip Coating as Piezoresistive Pressure Sensor for Human Motion Detection

Flexible and wearable pressure sensor may offer convenient, timely, and portable solutions to human motion detection, yet it is a challenge to develop cost-effective materials for pressure sensor with high compressibility and sensitivity. Herein, a cost-efficient and scalable approach is reported to prepare a highly flexible and compressible conductive sponge for piezoresistive pressure sensor. The conductive sponge, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)@melamine sponge (MS), is prepared by one-step dip coating the commercial melamine sponge (MS) in an aqueous dispersion of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Due to the interconnected porous structure of MS, the conductive PEDOT:PSS@MS has a high compressibility and a stable piezoresistive response at the compressive strain up to 80%, as well as good reproducibility over 1000 cycles. Thereafter, versatile pressure sensors fabricated using the conductive PEDOT:PSS@MS sponges are attached to the different parts of human body; the capabilities of these devices to detect a variety of human motions including speaking, finger bending, elbow bending, and walking are evaluated. Furthermore, prototype tactile sensory array based on these pressure sensors is demonstrated.

Natural α-methylenelactam analogues: Design, synthesis and evaluation of α-alkenyl-γ and δ-lactams as potential antifungal agents against Colletotrichum orbiculare

In our continued efforts to improve the potential utility of the α-methylene-γ-lactone scaffold, 62 new and 59 known natural α-methylenelactam analogues including α-methylene-γ-lactams, α-arylidene-γ and δ-lactams, and 3-arylideneindolin-2-ones were synthesized as the bioisosteric analogues of the α-methylenelactone scaffold. The results of antifungal and cytotoxic activity indicated that among these derivatives compound (E)-1-(2, 6-dichlorobenzyl)-3-(2-fluorobenzylidene) pyrrolidin-2-one (Py51) possessed good selectivity with the highest antifungal activity against Colletotrichum orbiculare with IC₅₀ = 10.4 μM but less cytotoxic activity with IC₅₀ = 141.2 μM (against HepG2 cell line) and 161.2 μM (against human hepatic L02 cell line). Ultrastructural change studies performed by transmission electron microscope showed that Py51 could cause important cell morphological changes in C. orbiculare, such as plasma membrane detached from cell wall, cell wall thickening, mitochondria disruption, a dramatic increase in vacuolation, and eventually a complete loss in the integrity of organelles. Significantly, mitochondria appeared one of the primary targets, as confirmed by their remarkably aberrant morphological changes. Analysis of structure-activity relationships revealed that incorporation of the aryl group into the α-exo-methylene and the N-benzyl substitution increased the activity. Meanwhile, the α-arylidene-γ-lactams have superiority in selectivity over the 3-arylideneindolin-2-ones. Based on the results, the N-benzyl substituted α-(2-fluorophenyl)-γ-lactam was identified as the most promising natural-based scaffold for further discovering and developing improved crop-protection agents.

The synthesis and structural characterization of twin liquid crystalline perylenebisimides

A smectic to nematic LC phase switch is achieved by changing one methylene unit in the central spacer segment.

A molecular nematic liquid crystalline material for high-performance organic photovoltaics

Solution-processed organic photovoltaic cells (OPVs) hold great promise to enable roll-to-roll printing of environmentally friendly, mechanically flexible and cost-effective photovoltaic devices. Nevertheless, many high-performing systems show best power conversion efficiencies (PCEs) with a thin active layer (thickness is ~100 nm) that is difficult to translate to roll-to-roll processing with high reproducibility. Here we report a new molecular donor, benzodithiophene terthiophene rhodanine (BTR), which exhibits good processability, nematic liquid crystalline behaviour and excellent optoelectronic properties. A maximum PCE of 9.3% is achieved under AM 1.5G solar irradiation, with fill factor reaching 77%, rarely achieved in solution-processed OPVs. Particularly promising is the fact that BTR-based devices with active layer thicknesses up to 400 nm can still afford high fill factor of ~70% and high PCE of ~8%. Together, the results suggest, with better device architectures for longer device lifetime, BTR is an ideal candidate for mass production of OPVs.

π-Conjugated polymer anisotropic organogel nanofibrous assemblies for thermoresponsive photonic switches

The present work demonstrates one of the first examples of π-conjugated photonic switches (or photonic wave plates) based on the tailor-made π-conjugated polymer anisotropic organogel. New semicrystalline segmented π-conjugated polymers are designed with rigid aromatic oligophenylenevinylene π-core and flexible alkyl chain along the polymer backbone. These polymers are found to be self-assembled as semicrystalline or amorphous with respect to the number of carbon atoms in the alkyl units. These semicrystalline polymers produce organogels having nanofibrous morphology of 20 nm thickness with length up to 5 μm. The polymer organogel is aligned in a narrow glass capillary, and this anisotropic gel device is further demonstrated as photonic switches. The glass capillary device behaves as typical λ/4 photonic wave plates upon the illumination of the plane polarized light. The λ/4 photonic switching ability is found to be maximum at θ = 45° angle under the cross polarizers. The orthogonal arrangements of the gel capillaries produce dark and bright spots as on-and-off optical switches. Thermoreversibility of the polymer organogel (also its xerogel) was exploited to construct thermoresponsive photonic switches for the temperature window starting from 25 to 160 °C. The organic photonic switch concept can be adapted to large number of other π-conjugated materials for optical communication and storage.

Succinate esters: odd-even effects in melting points

Dialkyl succinates show a pattern of alternating behavior in their melting points, as the number of C atoms in the alkane side chain increases, unlike in the dialkyl oxalates [Joseph et al. (2011). Acta Cryst. B67, 525-534]. Dialkyl succinates with odd numbers of C atoms in the alkyl side chain show higher melting points than the immediately adjacent analogues with even numbers. The crystal structures and their molecular packing have been analyzed for a series of dialkyl succinates with 1-4 C atoms in the alkyl side chain. The energy difference (ΔE) between the optimized and observed molecular conformations, density, Kitaigorodskii packing index (KPI) and C-H...O interactions are considered to rationalize this behavior. In contrast to the dialkyl oxalates where a larger number of moderately strong C-H...O interactions were characteristic of oxalates with elevated melting points, here the molecular packing and the density play a major role in raising the melting point. On moving from oxalate to succinate esters the introduction of the C2 spacer adds two activated H atoms to the asymmetric unit, resulting in the formation of stronger C-H...O hydrogen bonds in all succinates. As a result the crystallinity of long-chain alkyl substituted esters improves enormously in the presence of hydrogen bonds from activated donors.

Fluorescent cross-linked polystyrene perylenebisimide/oligo(p-phenylenevinylene) microbeads with controlled particle size, tunable colors, and high solid state emission

A series fo cross-linked fluorescent polystyrene (PS) microbeads with narrow size distribution and intense solid state emission was developed. Fluorophores based on perylene bisimide (PBI) and oligo(p-phenylenevinylene) (OPV) designed as acrylic cross-linkers were introduced into the polymerization recipe in a two-stage dispersion polymerization, carried out in ethanol in the presence of poly(vinylpyrrolidone) (PVP) as stabilizer. The structural design permitted introduction of up to 10(-5) moles of the fluorophores into the polymerization medium without fouling of the dispersion. The particle size measured using dynamic light scattering (DLS) indicated that they were nearly monodisperse with size in the range 2-3 μm depending on the amount of fluorophore incorporated. Fluorescence microscope images of ethanol dispersion of the sample exhibited intense orange red emission for PS-PBI-X series and green emission for PS-OPV-X series. A PS incorporated with both OPVX and PBIX exhibited dual emission upon exciting at the OPV wavelength of 350 nm and PBI wavelength of 490 nm, respectively. The low incorporation of fluorophore resulted in almost complete absence of aggregation induced reduction in fluorescence as well as red-shifted aggregate emission. The solid state emission quantum yield measured using integrating-sphere setup indicated a very high quantum yield of ϕpowder = 0.71 for PS-OPV-X and ϕpowder = 0.25 for PS-PBI-X series. The cross-linked PS microbeads incorporating both OPV and PBI chromophores had a ϕpowder = 0.33 for PBI emission and ϕpowder = 0.20 for OPV emission. This strategy of introducing fluorophore as cross-linkers into the PS backbone is very versatile and amenable to simultaneous addition of different suitably designed fluorophores emitting at different wavelengths.

Solid state assemblies and photophysical characteristics of linear and bent-core π-conjugated oligophenylenevinylenes

New classes of luminescent linear, bent-core, and star-shaped oligophenylenevinylenes (OPVs) having 1,4-para and 1,3-meta rigid aromatic cores were designed and developed. 3-Pentadecylphenol, a renewable resource molecule, was chosen as the flexible unit at the longitudinal or middle position of the OPV aromatic core for solid state ordering. Depending upon the nature of the π-core, the OPVs exhibited either mosaic-type liquid crystalline textures or spherulitic crystalline solids. The enthalpies of melting transitions revealed that the bent-core OPV structure showed enhanced solid state packing compared to linear or star-shaped OPVs. Small and wide-angle X-ray diffraction analysis confirmed layered-like assemblies in OPV molecules. Photophysical experiments such as excitation, emission, and time-resolved fluorescence decay dynamics were carried out to trace the molecular self-organization of OPV chromophores. Time correlated single photon counting technique (TCSPC) luminescent decay profiles and decay lifetimes (τ1 and τ2 values) revealed that the OPV chromophores showed faster exciton decay in the tightly packed bent-core structure. The weakly packed star-shaped OPV showed enhanced excited state luminescence stability up to 10 ns. A direct correlation between the OPV chemical structure, solid state ordering, and photophysical characteristics was established.

Inhibition of Acyl-CoA: cholesterol acyltransferase (ACAT), overexpression of cholesterol transporter gene, and protection of amyloid β (Aβ) oligomers-induced neuronal cell death by tricyclic pyrone molecules

A major effort in Alzheimer's disease therapeutic development has targeted Aβ and downstream events. We have synthesized a small library of tricyclic pyrone compounds. Their protective action in MC65 cells and inhibition of ACAT along with the upregulation of cholesterol transporter gene were investigated. Five active compounds exhibited potencies in the nanomolar ranges. The multiple effects of the compounds on Aβ and cellular cholesterol pathways could be potential mechanisms underlying the protective effects in vivo.

Synthesis of a 2,2'-bipyridyl functionalized oligovinylene-phenylene using Heck and Horner-Wadsworth-Emmons reactions and X-ray crystal structure of E-(4-(4-bromostyryl)phenyl)(methyl)sulfane

The synthesis of a new 2,2'-bipyridyl functionalized oligovinylenephenylene (OVP-5) containing a methyl protected thiol using Heck coupling and the Horner-Wadsworth-Emmons reaction and is described. A key step involving a diisopropylcarbodiimide promoted dehydration of a stable β-hydroxyphosphonate intermediate was identified. The structure of precursor E-(4-(4-bromostyryl)phenyl)(methyl)sulfane (1) was determined using X-ray crystallography.