Direct Writing of Room Temperature Polariton Condensate Lattice.

Realizing lattices of exciton polariton condensates has been of much interest owing to the potential of such systems to realize analogue Hamiltonian simulators and physical computing architectures. Here, we report the realization of a room temperature polariton condensate lattice using a direct-write approach. Polariton condensation is achieved in a microcavity embedded with host-guest Frenkel excitons of an organic dye (rhodamine) in a small-molecule ionic isolation lattice (SMILES). The microcavity is patterned using focused ion beam etching to realize arbitrary lattice geometries, including defect sites on demand. The band structure of the lattice and the emergence of condensation are imaged using momentum-resolved spectroscopy. The introduction of defect sites is shown to lower the condensation threshold and result in the formation of a defect band in the condensation spectrum. The present approach allows us to study periodic, quasiperiodic, and disordered polariton condensate lattices at room temperature using a direct-write approach.

Self-assembled Trehalose Amphiphiles as Molecular Gels: A Unique Formulation to Wax-free Cosmetics.

Trehalose has been used as an emollient and antioxidant in cosmetics. However, we aimed to explore trehalose amphiphiles as oil structuring agents for the preparation of gel-based lip balms as part of wax-free cosmetics. This article describes the synthesis of trehalose fatty acyl amphiphiles and their corresponding oleogel-based lip balms. Trehalose dialkanoates were synthesized by esterifying the two primary hydroxyls of trehalose with fatty acids (C4-C12) using a facile, regioselective lipase catalysis. The gelation potential of as-synthesized amphiphiles was evaluated in organic solvents and vegetable oils. Stable oleogels were subjected to X-ray diffraction (XRD), thermal (DSC), and rheological studies and further used for the preparation of lip balms. Trehalose dioctanoate (Tr8), trehalose didecanoate (Tr10) were found to be super gelators as their minimum gelation concentration is ≤ 0.2 wt%. XRD studies revealed their hexagonal columnar molecular packing while forming the fibrillar networks. Rheometry proved that the fatty acyl chain length of amphiphiles can influence the strength and flow properties of oleogels. Further rheometry (at 25 °C, 37 °C, and 50 °C) and DSC studies have validated that Tr8- and Tr10-based oleogels are stable for commercial applications. Tr8- and Tr10-based olive oil oleogels were used for the preparation of lip balms. The preliminary results suggested that the cumulative effect of trehalose's emolliency and vegetable oil gelling nature can be achieved with trehalose amphiphiles, specifically, Tr8 and Tr10. This study has also demonstrated that Tr8- and Tr10-based lip balms can be used as an alternative to beeswax and plant wax lip balms, indicating their huge potential to succeed as a new paradigm to formulate wax-free cosmetics.

Thermalization of Fluorescent Protein Exciton-Polaritons at Room Temperature.

Fluorescent proteins (FPs) have recently emerged as a serious contender for realizing ultralow threshold room temperature exciton-polariton condensation and lasing. This contribution investigates the thermalization of FP microcavity exciton-polaritons upon optical pumping under ambient conditions. Polariton cooling is realized using a new FP molecule, called mScarlet, coupled strongly to the optical modes in a Fabry-Pérot cavity. Interestingly, at the threshold excitation energy (fluence) of ≈9 nJ per pulse (15.6 mJ cm-2 ), an effective temperature is observed, Teff  ≈ 350 ± 35 K close to the lattice temperature indicative of strongly thermalized exciton-polaritons at equilibrium. This efficient thermalization results from the interplay of radiative pumping facilitated by the energetics of the lower polariton branch and the cavity Q-factor. Direct evidence for dramatic switching from an equilibrium state into a metastable state is observed for the organic cavity polariton device at room temperature via deviation from the Maxwell-Boltzmann statistics at k‖  = 0 above the threshold. Thermalized polariton gases in organic systems at equilibrium hold substantial promise for designing room temperature polaritonic circuits, switches, and lattices for analog simulation.

Selective isomer emission via funneling of exciton polaritons.

Polaritons in organic systems has shown the potential to modify chemical properties and to mediate long-range energy transfer between individual chromophores, among other capabilities. Here, we demonstrate that strong coupling and formation of organic exciton-polaritons can be used to selectively tune the isomer emission of organic molecules. By taking advantage of their delocalized and hybrid character, polaritons emerging in the strong coupling regime open a new relaxation pathway that allows for an efficient funneling of the excitation between the molecular isomers. We implement this by strong coupling to trans-DCS (E-4-dimethylamino-4'cyanostilbene)molecules, which present two isomers in different amounts when immersed in a polymer matrix. Thanks to this new relaxation pathway, the photoexcitation that is first shared by the common polaritonic mode is then selectively funneled to the excited states of one of the isomers, recognizing pure emission from the isomeric states that do not contribute to emission under normal conditions.

Light-Assisted Rechargeable Lithium Batteries: Organic Molecules for Simultaneous Energy Harvesting and Storage.

Lithium batteries that could be charged on exposure to sunlight will bring exciting new energy storage technologies. Here, we report a photorechargeable lithium battery employing nature-derived organic molecules as a photoactive and lithium storage electrode material. By absorbing sunlight of a desired frequency, lithiated tetrakislawsone electrodes generate electron-hole pairs. The holes oxidize the lithiated tetrakislawsone to tetrakislawsone while the generated electrons flow from the tetrakislawsone cathode to the Li metal anode. During electrochemical operation, the observed rise in charging current, specific capacity, and Coulombic efficiency under light irradiation in contrast to the absence of light indicates that the quinone-based organic electrode is acting as both photoactive and lithium storage material. Careful selection of electrode materials with optimal bandgap to absorb the intended frequency of sunlight and functional groups to accept Li-ions reversibly is a key to the progress of solar rechargeable batteries.

Tuning Aesthetic and Mechanical Properties of Oleogels via Formulation of Enzyme-Enabled Stereoisomeric Molecular Gelators.

The mechanistic resemblance of oil-based molecular gels (oleogels) to solid fats (trans and saturated) makes molecular gelation an ideal alternative in developing fat-based food and cosmetic products. The recent upsurge in the preference for oleogels (structured oils) is due to them being healthier than conventional solid fats. The present study reveals a simple means of modulating the mechanical and aesthetic properties of oleogels by physically mixing two isomeric low-molecular-weight gelators, mannitol dioctanoate (M8) and sorbitol dioctanoate (S8), which have contrasting oil-structuring behaviors; while M8 formed oleogels with a higher gel strength, the S8 gels were more aesthetic, translucent, and appealing. The gelators were synthesized by enzyme catalysis (a generally regarded as safe protocol). The M8/S8 gels were systematically and thoroughly characterized using a suite of analytical techniques, including minimum gelation concentration, gel melting point, rheological storage modulus, oil binding capacity, light transmittance, and optical microscopy. The results showed that the percentage of light transmittance, which is associated with aesthetics, increased from about 40 to 95% with an increasing fraction of S8 from 0 to 1. Parameters associated with mechanical strength, such as rheology, were also quite responsive to varying proportions of the gelators. The storage modulus (G', a rheological property) increased from about 3300 to about 12 500 Pa with an increasing fraction of M8. As the fraction of M8 increased, the solid fat content (SFC) changed from about 3.51 to 2.08%, while the oil binding capacity changed from about 70.2 to 100.0. This work enables the modulation of the aesthetic and organoleptic properties of a gel via a simple formulation of stereoisomeric molecular gelators.

Bioderived Molecular Electrodes for Next-Generation Energy-Storage Materials.

Invited for this month's cover are the groups of George John at the City College of New York-CUNY, Leela R. Arava at Wayne State University, and Pulickel Ajayan at Rice University. The image portraits future prospects of bioderived molecular electrodes for next-generation energy-storage materials. The Minireview itself is available at 10.1002/cssc.201903589.

Bioderived Molecular Electrodes for Next-Generation Energy-Storage Materials.

Nature-derived organic small molecules, as energy-storage materials, provide low-cost, recyclable, and non-toxic alternatives to inorganic and polymer electrodes for lithium-/sodium-ion batteries and beyond. Some organic carbonyl compounds have met or exceeded the voltages and gravimetric storage capacities achieved by traditional transition metal oxide-based compounds due to the metal-ion coupled redox and facile electron-transport capability of functional groups. Stability issues that previously limited the capacity of small organic molecules can be remediated with reactions to form insoluble salts, noncovalent interactions (hydrogen bonding and π stacking), loading onto substrates, and careful electrolyte selection. The cost-effectiveness and sustainability of organic materials may further be improved by employing porphyrin-based electrodes and multivalent-ion batteries utilizing abundant metals, such as aluminum and zinc. Finally, redox flow batteries take advantage of the solubility of organics for the development of scalable, high power density, and safe energy-storage devices based on aqueous electrolytes. Herein, the advantages and prospects of small molecule-based electrodes, with a focus on nature-derived organic and biomimetic materials, to realize the next-generation of green battery chemistry are reviewed.

Freestanding organogels by molecular velcro of unsaturated amphiphiles.

A simple amphiphile, N-cardanyltaurine amide (NCT) with different degrees of cis-unsaturation in its tail resulted in the formation of strong organogels. Interestingly, this is in contrast to the commonly accepted notion that introducing unsaturation in alkyl chains enhances fluidity in lipid assemblies. The physico-chemical and first-principles DFT calculations confirmed the pegging of 'kinked' unsaturated side chains, where the hydrophobic interlocking as in Velcro fasteners leads to a network of cylindrical micelles, resulting in self-standing organogels. Textural profile analysis and spectroscopic details substantiated the dynamic assembly to resemble a 3D network of gelators rather than being a cross-linked or polymerized matrix of monomers.

Phenothiazine-Based Oligo(p-phenylenevinylene)s: Substituents Affected Self-Assembly, Optical Properties, and Morphology-Induced Transport.

Designing intramolecular charge-transfer (ICT)-based luminogenic ordered assemblies exhibiting significant electrical transport is a challenging task in the field of organic optoelectronics. In this context, a series of novel phenothiazine-based oligo(p-phenylenevinylene) (OPV1-6) derivatives were designed and their structure-property relationship was investigated. Upon examining their photophysical properties, all the OPVs were found to exhibit significant intramolecular charge-transfer characteristics in organic solvents. While inspecting the self-assembly behaviour, the OPV with a long alkyl chain on the central phenyl core (OPV4) underwent gelation in organic solvent mixtures through strong hydrophobic interactions of the long hexadecyl chains and π-interactions from their aromatic counterparts. Computational studies revealed a lamellar packing of molecules in the assembly. Interestingly, the degree of ICT and the gelation abilities of OPVs were significantly influenced by the electronic nature of the substituents appended to the peripheral phenothiazines. Further, the AC impedance results revealed an increase in storage and electronic transport for the fluorescent thin films prepared by an increase in the content of OPV4 in PMMA.

Augmenting Photoinduced Charge Transport in a Single-Component Gel System: Controlled In Situ Gel-Crystal Transformation at Room Temperature.

Smart single-component materials with versatile functions require pre-programming of a higher order molecular assembly. An electroactive supergelator (c=0.07 wt %) triphenylamine core-appended poly(aryl ether) dendron (TPAPAE) is described, where substantial dendritic effects improve the order and crystallinity by switching the local minima from self-assembled molecular wires to thermodynamically favorable global minima of ordered crystals, ripened within the fibers. Controlled in situ phase change at room temperature ultimately stabilized the mixed valence states in the single-component supramolecular assembly with photoluminescence and photoinduced charge transport amplified by two orders of magnitude.

Charge Transfer Modulated Self-Assembly in Poly(aryl ether) Dendron Derivatives with Improved Stability and Transport Characteristics.

Alteration of native gelation properties of anthracene and pyrene cored first generation poly(aryl ether) dendrons, G1-An and G1-Py, by introducing a common acceptor, 2,4,7-trinitro-9H-fluoren-9-one (TNF), results in forming charge transfer gels in long chain alcoholic solvents. This strategy leads to significant perturbation of optical and electronic properties within the gel matrix. Consequently, a noticeable increase of their electrical conductivities is observed, making these poly(aryl ether) dendron based gels potential candidates for organic electronics. While the dc-conductivity (σ) value for the native gel from G1-An is 2.8 × 10-4 S m-1, the value increased 3 times (σ = 8.7 × 10-4 S m-1) for its corresponding charge transfer gel. Further, the dc-conductivity for the native gel self-assembled from G1-Py dramatically enhanced by approximately an order of magnitude from 4.9 × 10-4 to 1.3 × 10-3 S m-1, under the influence of an acceptor. Apart from H-bonding and π···π interactions, charge transfer results in the formation of a robust 3D network of fibers, with improved aspect ratio, providing high thermo-mechanical stability to the gels compared to the native ones. The charge transfer gels self-assembled from G1-An/TNF (1:1) and G1-Py/TNF exhibit a 7.3- and 2.5-fold increase in their yield stress, respectively, compared to their native assemblies. A similar trend follows in the case of their thermal stabilities. This is attributed to the typical bilayer self-assembly of the former which is not present in the case of G1-Py/TNF charge transfer gel. Density functional calculations provide deeper insights accounting for the role of charge transfer interactions in the mode of self-assembly. The 1D potential energy surface for the G1-An/TNF dimer and G1-Py/TNF dimer is found to be 11.8 and 1.9 kcal mol-1 more stable than their corresponding native gel dimers, G1-An/G1-An and G1-Py/G1-Py, respectively.