Aggregation-induced emission of 1-methyl-1,2,3,4,5-pentaphenylsilole

Mimics of the self-assembling chlorosomal bacteriochlorophylls: regio- and stereoselective synthesis and stereoanalysis of acyl(1-hydroxyalkyl)porphyrins

Diacylation of copper 10,20-bis(3,5-di-tert-butylphenylporphyrin) using Friedel-Crafts conditions at short reaction times, high concentrations of catalyst, and 0-4 degrees C affords only the 3,17-diacyl-substituted porphyrins, out of the 12 possible regioisomers. At longer reaction times and higher temperatures, the 3,13-diacyl compounds are also formed, and the two isomers can be conveniently separated by normal chromatographic techniques. Monoreduction of these diketones affords in good yields the corresponding acyl(1-hydroxyalkyl)porphyrins, which after zinc metalation are mimics of the natural chlorosomal bacteriochlorophyll (BChl) d. Racemate resolution by HPLC on a variety of chiral columns was achieved and further optimized, thus permitting easy access to enantiopure porphyrins. Enantioselective reductions proved to be less effective in this respect, giving moderate yields and only 79% ee in the best case. The absolute configuration of the 3(1)-stereocenter was assigned by independent chemical and spectroscopic methods. Self-assembly of a variety of these zinc BChl d mimics proves that a collinear arrangement of the hydroxyalkyl substituent with the zinc atom and the carbonyl substituent is not a stringent requirement, since both the 3,13 and the 3,17 regioisomers self-assemble readily as the racemates. Interestingly, the separated enantiomers self-assemble less readily, as judged by absorption, fluorescence, and transmission electron microscopy studies. Circular dichroism spectra of the self-assemblies show intense Cotton effects, which are mirror-images for the two 3(1)-enantiomers, proving that the supramolecular chirality is dependent on the configuration at the 3(1)-stereocenter. Upon disruption of these self-assemblies with methanol, which competes with zinc ligation, only very weak monomeric Cotton effects are present. The favored heterochiral self-assembly process may also be encountered for the natural BChls. This touches upon the long-standing problem of why both 3(1)-epimers are encountered in BChls in ratios that vary with the illumination and culturing conditions.

Aggregation-enhanced emission in gold nanoparticles protected by tetradentate perylene derivative

Three novel gold nanoparticle (AuNPs) composites protected by perylene bisimide derivatives have been designed and synthesized. Thanks to the rational molecular design, AuNPs capped by N,N'-2,6-bis(4-aminomethylpyridine)-1,6,7,13-tert-[4-(hydroxymethyl)phenoxy-5-(1,2-dithiolan-3-yl)pentanoate]-3,4,9,10- tetracarboxylic acid bisimide (8SP-AuNPs) exhibited unusual enhancement in fluorescence intensity, while the other two nanoparticle composites showed slight enhancement or quench in emission spectra. The structural effect of ligands on aggregation enhanced emission had been studied, and temperature dependence experiments had been conducted. Deductive explanation had been made to elucidate the special spectral behavior of 8SP-AuNPs led by restricted motion of perylene chromophores in the packed nanoclusters.

Dendritic effect on supramolecular self-assembly: organogels with strong fluorescence emission induced by aggregation

A novel class of dumbbell-shaped dendritic molecules with a p-terphenylene core was synthesized, and their self-assembling properties were investigated. The incorporation of bulky dendritic wedges to the central stiff aromatic scaffolds could finely tune their solubility in many organic solvents. Unlike the self-assembly behavior of p-terphenylen-1,4"-ylenebis(dodecanamide), the p-terphenylene cored different generation dendritic molecules could form gels in several kinds of organic solvents through a cooperative effect of the pi-pi stacking, hydrogen-bonding, and van der Waals forces. Interestingly, significant fluorescence enhancement was observed after gelation. Extensive investigations with atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), theological measurements, UV-vis absorption spectroscopy, FT-IR spectroscopy, 1H NMR, and X-ray powder diffraction (XRD) revealed that these dendritic molecules self-assembled into elastically interpenetrating one-dimensional nanostructures in organogels.

Design and self-assembly of L-glutamate-based aromatic dendrons as ambidextrous gelators of water and organic solvents

A series of L-glutamate-based dendrons containing aromatic cores ranging from phenyl to naphthyl to anthryl were synthesized, and their self-assembly in organic solvents as well as in water was investigated. It was found that all of these dendrons formed organogels with hexane and simultaneously formed the hydrogels with water, thus exhibiting ambidextrous properties. Nanofiber structures are essentially formed in organogels and hydrogels, and some nanostrips are formed in some of the hydrogels. During gel formation, both hydrogen bonds between the amide groups and the pi-pi stacking between the aromatic rings played a predominant role in forming the ID nanostructures. Both the hydrogels and the organogels containing naphthyl and anthryl groups showed fluorescence emission. In comparison with the corresponding compounds in solution, the naphthyl-containing dendrons showed a strong enhancement of fluorescence in the gel. In the case of anthryl-containing dendrons, fluorescence enhancement was observed for the derivative with anthryl substituted at the 9 position, whereas a decrease was observed for the gels of the 2-substituted derivative. Although the chirality of L-glutamate could not be transferred to the aromatic chromophores in solution, it was transferred to the chromophores in gels as a result of the self-assembly and strong pi-pi interaction of the gelators. On the basis of the properties of the organogels and hydrogels, a thermally driven chiroptical switch was proposed. That is, the chirality disappeared when the gel was heated to solution, whereas it returned when cooled to a gel. The process can be repeated many times.

Synthesis, optical, and mesomorphic properties of self-assembled organogels featuring phenylethynyl framework with elaborated long-chain pyridine-2,6-dicarboxamides

A series of new organogelators with pi-conjugated phenylethynyl framework featuring long-chain carboxamides have been synthesized. These organgelators have shown great ability to gel a variety of organic solvents to form stable organogels with the minimum gelation concentration as low as 0.1 wt %. Gelation is completely thermoreversible, and it occurs due to the aggregation of the organogelators resulting in the formation of a fibrous network via a combination of intermolecular hydrogen bonding, pi-pi stacking, and van der Waals interactions that is observed for the xerogels by TEM. The influence of sol-to-gel transition has been explored in detail by variable-temperature 1H NMR, UV-vis absorption, and fluorescence spectroscopy. Aggregation-induced enhanced emission has been observed in these organogelator molecules with an order of higher fluorescence quantum yields from solution to gels. In addition, some molecules also exhibit unique liquid crystalline properties over a large temperature range as revealed by DSC and POM studies.

A fluorescent thermometer operating in aggregation-induced emission mechanism: probing thermal transitions of PNIPAM in water

Poly(N-isopropylacrylamide) was labelled using a fluorogen with an aggregation-induced emission feature by direct polymerization; the label served as a fluorogenic probe that reveals fine details in the thermal transitions in the aqueous solution of the polymer; the working mode was readily tuned between non-monotonic and monotonic by changing the labelling degree of the polymer.

Hydrogen-bonded dimer stacking induced emission of aminobenzoic acid compounds

A series of aminobenzoic acid crystals with stacking-induced emission properties has been achieved and the packing structures of the hydrogen-bonded acid dimers provided an explanation for the emission characteristics of the crystals.

Sugar-phosphole oxide conjugates as "turn-on" luminescent sensors for lectins

A mixture of sugar-phosphole oxide conjugates and lectins in a buffer solution displays an intense blue emission, thereby acting as a "turn-on" fluorescent sensor for lectins as they form aggregates.

Continuous on-site label-free ATP fluorometric assay based on aggregation-induced emission of silole

In this letter, we have described the establishment of a label-free fluorometric assay to detect adenosine triphosphate (ATP), which can enable the monitoring of the ATP hydrolysis process continuously and in situ. This assay is based on a silole derivative with positively charged modifications, compound 1, that can aggregate on the negative charged ATP template through charge-charge interaction. Because the silole group has strong aggregation-induced fluorescence emission (AIE), we have found that the aggregation could induce strong fluorescence emission and its intensity is positively and linearly related to the ATP concentration. Meanwhile, 1 also shows good discrimination for ATP, where its hydrolysis products ADP, AMP, and adenosine could not induce sufficient aggregation to produce a strong fluorescence signal. These characteristics are sufficient to build up a sensitive fluorescence assay to monitor the ATP concentration change in solution in situ, and we have also verified its usability in studying the reaction process of phosphatase.

Organic styryl dye nanoparticles: synthesis and unique spectroscopic properties

We report the synthesis and unique spectroscopic properties of organic styryl dye nanoparticles. Aqueous-phase ion association between a cationic styryl dye 2-(4-(dimethylamino)styryl)-1-ethylpyridinium (DASPE), possessing both electron donor and acceptor groups in its molecule, and tetraphenylborate (TPB) or tetrakis(4-fluorophenyl)borate (TFPB) anion, in the presence of poly(vinylpyrrolidone), produces the ion-based dye (DASPE) nanoparticles of approximately 30-100 nm in diameter. Absorption spectra of the DASPE nanoparticles show a large bathochromic shift in comparison with that of the dye monomer in water. Quantum chemical calculations demonstrate that ion-pair formation brings about a large internal rotation around a single bond in DASPE, and this internal twisting as well as local polarity of the counteranion have a strong influence on the red shift of the optical spectra. Furthermore, nanoparticle formation results in enhanced fluorescence of DASPE: more than a 20-fold enhancement in the fluorescence quantum yield as compared to that of the dye monomer in water, giving a new methodology for the synthesis of fluorescent organic nanoparticles. The observed fluorescence would come from an intramolecular charge-transfer (ICT) excited state stabilized by the matrix of TPB or TFPB, and the enhancement is due to both the high rotational resistance for the single bond in DASPE and the matrix polarity effect that can suppress the nonradiative processes.