Functional Small Molecules Research Articles

Optical properties of one-dimensional nanomaterials based on small organic molecules

One-dimensional (1D) nanomaterials synthesized from opto-functional low-molecular-weight organic compounds have drawn great interests for their unique optical properties and potential applications in high speed miniaturized photonic integrations. Compared with their inorganic counterparts, organic nanostructures offer advantages such as their high reactivity, ease of chemical doping and convenience in processing at low temperature. In this article, we begin with a general overview of recent progress in this research area. After that, the construction strategies for achieving 1D nanostructures from small organic functional molecules are introduced. Then we focus on the unique optical properties induced by molecular aggregation in the nanostructures, such as optical waveguide, stimulated emission and electroluminescence. This article concludes with a summary and our perspective about future development in 1D organic molecular nanomaterials and organic integrated photonic devices.

High-Quality Large-Size Organic Crystals Prepared by Improved Physical Vapor Growth Technique and Their Optical Gain Properties

We have developed an improved physical vapor transport method. This method enables us to decrease the sublimation temperature of small organic molecules, and slow the weight loss process, and then regulate the degree of vapor saturation of materials. Large-size single-crystalline materials with high quality are successfully prepared from small organic functional molecules. The slice crystals are found to be single crystalline with high quality. The surface morphologies and structural information of grown crystals were characterized by optical microscope, atomic force microscopy (AFM), and X-ray diffraction (XRD) analysis. The results indicate that the growth mechanism of single crystals is a 2D nucleation, with elementary steps, large straight steps, and layer-by-layer growth.

Selective Covalent Labeling of Tag-Fused GPCR Proteins on Live Cell Surface with a Synthetic Probe for Their Functional Analysis

Selective protein labeling with a small molecular probe is a versatile method for elucidating protein functions in living cells. In this paper, we report a covalent labeling method of tag-fused G-protein coupled receptor (GPCR) proteins expressing on cell surfaces utilizing small functional molecules. This method employs the selective and rapid reaction of a peptide tag and a molecular probe, which comprises the cysteine-containing short CA6D4x2 tag (CAAAAAADDDDGDDDD) and a tetranuclear Zn(II)-DpaTyr probe containing a reactive alpha-chloroacetyl moiety. The covalent labeling of tag-fused GPCRs such as bradykinin receptor (B2R) and acetylcholine receptor (m1AchR) selectively proceeded under physiological conditions during short incubation (10-30 min) with Zn(II)-DpaTyr probes bearing various functional groups. Labeling with fluorophore-appended Zn(II)-DpaTyr probes enabled visualization of the GPCRs on the surface of HEK293 cells by fluorescence. Labeling with the biotin-appended probe allowed introduction of a biotin unit into the GPCRs. This biotin label was utilized for fluorescence bioimaging studies and postlabeling blotting analysis of the labeled GPCRs by use of the specific biotin-streptavidin interaction. The utility of this labeling method was demonstrated in several function analyses of GPCRs, such as fluorescence visualization of the stimuli-responsive internalization of GPCRs and pH change in endosomes containing the internalized GPCRs.

Photoresponsive Pseudopolyrotaxane Hydrogels Based on Competition of Host–Guest Interactions

Reversibility is a basic and crucial feature of supramolecular systems. In designing and fabricating new supramolecular materials, the realization of reversibility is particularly important as it could enable these substances to be superior to conventional materials. An excellent example is an elastomer reported recently, made of small functional molecules which form both long chains and cross-linkers through intermolecular multiple hydrogen bonding. When broken or cut, the elastomer can be simply repaired by just bringing together the fractured surfaces and allowing the recovery of the hydrogen bonding. There are plenty of reports on supramolecular assemblies of polymers showing reversible responses to environmental changes; however, these are mostly based on the inherent stimuli-sensitive properties of the building blocks, such as the temperature-induced coil–globule transition of poly(N-isopropyl acrylamide) (PNIPAM) and pH-induced protonation of poly(vinyl pyridine), rather than the reversibility of the supramolecular interactions. Therefore, taking full advantage of the reversibility of the noncovalent interactions to construct supramolecular materials is still a big challenge. This has drawn increasing interest in recent years, and has led to a series of promising results. For example, some hydrophobically modified water-soluble polymers realized sol–gel transition as a result of the reversible interactions of cyclodextrin and alkyl chains. The assembly and disassembly of polymeric vesicles can be controlled by photosensitive interactions between cyclodextrin and azobenzene compounds. The self-assembly of polyethylene glycol (PEG) and a-cyclodextrins (a-CDs) to form linear pseudopolyrotaxane (PPR), with PEG as the axis and a-CDs as threaded rings, was reported by Harada et al. Since the ability of PPR to form physical hydrogels was first reported in 1994, the system has been extensively studied as the hydrogels show very promising uses as biomedicine materials. There is now good understanding of the formation mechanisms and structures of such PPR hydrogels, but little has been explored concerning their dissociation and reassembly, though increasing temperature and shearing could make the hydrogel turn to a sol. Herein, we demonstrate a facile photocontrollable supramolecular route to realize the disassembly and reassembly of the PPR hydrogels. The addition of a photoresponsive compound containing an azobenzene moiety to the PPR hydrogel was found to be effective in converting the hydrogels to transparent solutions. By subsequent alternation of UVand visible irradiation, reversible sol-to-gel and gel-to-sol transitions were observed. Thus, the widely investigated PEG/aCD PPR hydrogel is proved to be “active” in supramolecular chemistry, and the reversible nature of supramolecular materials is fully realized. In our study, the PPR hydrogel (Figure 1a) was prepared by using PEG10K (molecular weight 10000) and a-CD in water as described in reference [7c]. The concentrations of

Layered organic–inorganic hybrid perovskites: structure, optical properties, film preparation, patterning and templating engineering

Organic–inorganic perovskites are a class of interesting compound in the perovskite family due to their unique structures of alternately stacking sheets of organic and inorganic components on the molecular scale. In this highlight, the basic knowledge and recent advances in organic–inorganic perovskites are reviewed with particular emphasis on the feature work including: the novel <110>- and <111>-oriented perovskite structures, synthesis, film preparation, patterning methods and optoelectronic properties of hybrid perovskites. Moreover, the small functional organic molecules can be templated into a regular arrangement by the inorganic perovskite framework. This unique material with nature-formed lamellar structure has the potential to be used as a template to create novel derivatives and bring about unique physical properties. Some interesting examples, such as intercalated polymer and silica network by topochemical polymerisation, fabrication of disk-like semiconductor nanocrystals and metal nanoparticles by hybrid perovskite templates are described.

Hierarchical functional gradients of pH-responsive self-assembled monolayers using dynamic covalent chemistry on surfaces

Surface chemistry is an important field of research, especially for the study and design of (bio)nanostructures in which nearly every atom lies at an interface. Here we show that dynamic covalent chemistry is an efficient tool for functionalizing surfaces in such a way that their interfacial properties can be varied controllably in space and time. Modulation of pH is used to tune the fast, selective and reversible attachment of functional amines (with different pK(a) values) to an aldehyde-coated surface. To illustrate the potential of this technique, we developed dynamic self-assembled monolayers ('DynaSAMs'), which enable the hierarchical construction of mixed gradients comprising either small functional molecules or proteins. Control of the (bio)chemical composition at any point on the surface potentially provides a simple bottom-up method to access numerous surface patterns with a broad range of functionalities.

Low‐Dimensional Nanomaterials Based on Small Organic Molecules: Preparation and Optoelectronic Properties

AbstractThis article presents a comprehensive review of recent progress of research dedicated to low‐dimensional nanomaterials constructed from functional low‐molecular‐weight organic compounds, whose optoelectronic properties are fundamentally different from those of their inorganic counterparts. After introducing the development of inorganic and organic macromolecular nanomaterials, we begin with a general review of the construction strategies for achieving both zero‐dimensional (0D) and one‐dimensional (1D) nanostructures from small organic functional molecules. We then provide an overview of the unique optoelectronic properties induced by molecular aggregation in the nanostructures. Special emphasis is put on the luminescent properties that are different from those of the corresponding bulk materials, such as aggregation‐induced enhanced emission, fluorescence narrowing, multicolor emission, and tunable and switchable emissions from doped nanostructures. We conclude with a summary and our personal view of the direction of future development of organic opto‐functional nanomaterials and devices.

Photoluminescence and Electroluminescence from Tris(8- hydroxyquinoline)aluminum Nanowires Prepared by Adsorbent-Assisted Physical Vapor Deposition

Single-crystalline nanowires are successfully prepared from a small organic functional molecule, tris(8-hydroxyquinoline)aluminum (Alq3), by an adsorbent-assisted physical-vapor-deposition method. The introduction of adsorbents can decrease the sublimation temperature of Alq3, and slow the weight-loss process markedly, which is proven to be indispensable in improving the uniformity of the as-prepared Alq3 nanowires. Measurements of the optical properties reveal that the absorption spectra of the Alq3 nanowires show an obvious blue-shift with decreasing diameter. The photoluminescence vibrational fine structure emerges and becomes pronounced with increasing excitation energy, which is attributed to the ordered orientation of the Alq3 molecules in the nanowires. Furthermore, the Alq3 nanowires are fabricated into an electroluminescent device, which has an obvious size-dependent performance.

A new approach to functionalize multi-walled carbon nanotubes by the use of functional polymers

A new method to graft a large number of long polymer chains or small functional molecules onto multi-walled carbon nanotubes (MWNTs) indirectly is reported. First, MWNTs were slightly functionalized by reversible addition–fragmentation chain transfer (RAFT) copolymerization of styrene and maleic anhydride using the dithioester groups attached to MWNTs as RAFT agents. The highly reactive maleic anhydride groups could further react with a large number of long polymer chains or small functional molecules with hydroxyl or amino group easily. The resulted MWNTs have good solubility in organic solvents and water; the perfect structure of MWNTs is altered very little from the information of Raman spectra.

2,4,5-Triphenylimidazole Nanowires with Fluorescence Narrowing Spectra Prepared through the Adsorbent-Assisted Physical Vapor Deposition Method

The single crystalline nanowires have been fabricated from a small organic functional molecule, 2,4,5-triphenylimidazole (TPI), through an adsorbent-assisted physical vapor deposition (PVD) method. The introduction of the absorbents can significantly improve the dimensional uniformity of the as-prepared TPI nanowires. The TPI nanowires displayed interesting size-dependent optical properties, that is, the absorption spectra of the wires exhibit an obvious blue shift with the decrease of diameter, and simultaneously, the vibrational fine structures of the emission spectra emerge and become more pronounced with the diameter decreasing from 500 to 40 nm even at room temperature, which are usually observed only under cryogenic conditions. The emergence and enhancement of the vibrational structures are contributed to the increase of the long-range order and the degree of orientation with the decrease of diameter. The strategy described here should give a useful enlightenment for the fabrication of wirelike nano...

Single Crystalline Submicrotubes from Small Organic Molecules

The single crystalline submicrotubes of a small organic functional molecule, 2,4,5-triphenylimidazole (TPI), were successfully prepared with a facile method. A series of characterizations indicated that the tubes were obtained from the rolling followed by seaming of a preorganized two-dimensional sheet-like structure, whose formation was due to the efficient cooperation of several molecular recognition elements. The length and diameter of the TPI tubes can be readily controlled by adjusting the experimental conditions. The as-prepared submicrotubes have intensive luminescence and size-dependent optical properties, which allows them to find potential applications in novel optical and optoelectronic devices together with their single crystalline structure and good stability. The strategy described here should give a useful enlightenment for the design and fabrication of tubular structures from small organic molecules.

Reversible self-polymerizing high Tg lyoprotectants

One mode of action of protectants in the storage of biological materials is by promoting the formation of a vitrified state on cooling or drying. In the case of preservation by drying, the glassy material comprises a low water content mixture of protectant and organic material. The protectant must on drying form a glassy state of glass transition temperature ( T g) above the desired storage temperature. However, in some applications it must also be easily transported through cell membranes and this restricts the choice to a relatively limited number of small molecules, which typically exhibit very low glass transition temperatures. In this work we describe a self-polymerizing protectant comprising an inorganic salt and a small hydroxy functional molecule such as glycerol. This forms co-ordinate polymer chains of high T g on drying but rapidly depolymerizes into the original components on rehydration. The polymerization process is general for polyhydroxy compounds including glucose and related compounds.