Topochemical polymerization of unsymmetrical aryldiacetylene supramolecules with nitrophenyl substituents utilizing C-H∙∙∙π interactions.

Diacetylenes are versatile building blocks, in which many functional groups can be incorporated for the construction of new materials with desirable properties. In this study, 6-(p or m-nitrophenyl)-3,5-hexadiyne-1-ol (4a or 4b) containing nitrophenyl groups (host) and 2-hydroxyethyl groups (guest) in different diacetylene terminals were designed to establish an ordered supramolecular assembly that is complied with the strict requirements for the topochemical polymerization of diacetylenes. Crystal film and bulk crystals of compound 4b were obtained successfully by cast film and re-precipitation methods. Both of these could photopolymerize to the corresponding regular poly(diacetylene) polymer, as evidenced by UV-vis, IR, FL and Raman spectroscopy. The electrochemical properties and behaviors of 4a and 4b were also investigated, and the results show that the differences between the para and meta positions of the mono-phenylacetylene substituents probably result from the topochemical polymerization. Thus, m-nitrophenylbutadiyne derivatives with sizeable C-H∙∙∙π interactions seemed to be effective for the formation of a polymerizable packing, which is appropriate for topochemical polymerization.

A method for enhancing the ocular penetration of eye drops using nanoparticles of hydrolyzable dye.

This report describes a method for enhancing the ocular penetration of eye drops using nanoparticles of hydrolyzable dye, which is similar to a prodrug approach. The entry of eye drops into the ocular globe is restricted predominantly by corneal barrier functions. The barrier functions are epithelial tight junctions as well as a physicochemical property consisting of the opposite characteristics of a lipophilic epithelium and a hydrophilic stroma. We found that using a formulation of nanoparticles of hydrolyzable dye (with particles of 200 nm in diameter on average) attained a greater than tenfold higher (about 50-fold) ocular penetration than that of micron-sized particles. The nanoparticles were prepared by a carrier-free technique; i.e., the reprecipitation method. Confocal laser fluorescence microscopy showed that dyes originating from the nanoparticles surmounted the corneal epithelium barrier, which has tight junctions, and achieved deeper penetration into the cornea. The high penetration rate of the dyes into the cornea was attributed to the size of particles (i.e., nanoparticles) and a transformation of dye polarity from lipophilic to hydrophilic in in vivo hydrolysis reactions. We concluded that utilizing in vivo hydrolysis reactions to alter the physicochemical nature of nanoparticles consisting of hydrolyzable compounds was an effective approach for enhancing the ocular penetration of eye drops.

Nanocrystallization of oligosilanes by a reprecipitation method: easy fabrication of H-aggregates of linear-chain oligosilane molecules.

Nanocrystals of several oligosilanes have been fabricated easily by using a reprecipitation method. The nanocrystals reveal an intense absorption band at the UVB region (280 to 320 nm) and a fluorescence band with large Stokes shift. These photophysical properties show that the nanocrystals exhibit an excitonic interaction of the H-aggregate type.

Introducing porosity into polyimide nanoparticles.

Novel porous polyimides (PIs) having diameters of several hundred nanometers have been fabricated successfully from precursor poly(amic acid) (PAA) derivatives with poly(acrylic acid) (PAS) as the porogen, using a reprecipitation method and subsequent imidization. The superficial high porosity with deep pores was introduced when using a more compatible combination of PAA and the porogen, i.e., PI (BPDA-PDA) and PAS rather than PI (10FEDA-4FMPD and PAS); the pore sizes ranged from 20 to 100 nm. The resulting porous PI nanoparticles had thermally stabilities (determined from their 5% weight loss temperatures at 400 degrees C) similar to those of corresponding PI nanoparticles lacking porous structures. Microphase separation within the PAA nanoparticles after reprecipitation induced the porous surface structure, the properties of which were influenced by the molecular weight of PAS and the chemical structure of PAA. These unique porous PI nanoparticles have great potential for application as low-k materials in next-generation technologies.

Combined molecular and supramolecular bottom-up nanoengineering for enhanced nonlinear optical response: experiments, modeling, and approaching the fundamental limit.

The authors study the combination of two independent strategies that enhance the hyperpolarizability of ionic organic chromophores. The first molecular-level strategy is the extension of the conjugation path in the active chromophore. The second supramolecular-level strategy is the bottom-up nanoengineering of an inclusion complex of the chromophore in an amylose helix by self-assembly. The authors study a series of five (dimethylamino)stilbazolium-type chromophores with increasing conjugation length between the (dimethylamino)phenyl donor ring and the pyridinium acceptor ring in conjunction with four amylose helices of differing molecular weights. The first hyperpolarizabilities of the self-assembled inclusion complexes, as determined with frequency-resolved femtosecond hyper-Rayleigh scattering at 800 and 1300 nm, are compared with experimental values for the free chromophores in solution and with theoretical values. While the experimental values for the hyperpolarizability in solution are lower than the theoretically predicted values, an enhancement upon inclusion is observed, with the longest chromophore in the best amylose helix showing an enhancement by one order of magnitude. Molecular modeling of the inclusion of the chromophore suggests that the coplanarity of the two rings is more important than all-trans configuration in the conjugation path. The fundamental limit analysis indicates that the inclusion inside the amylose helix results in an optimal excited-level energy spacing that is responsible for breaching the apparent limit.

In situ and ex situ observations of the growth dynamics of single perylene nanocrystals in water.

The growth dynamics of fluorescent perylene nanocrystals, which are fabricated by the reprecipitation method, was investigated using in situ and ex situ single-particle fluorescence measurements. A red shift in the emission maxima as the aging time increased was observed by single-particle fluorescence spectral measurements. The number and size of the nanocrystals increased with the increasing aging time in water. It was concluded that the metastable intermediates, such as clusters and initial nanoparticles, are relevant for the early stages of nucleation and growth of the perylene nanocrystals.

Synthesis and characterization of monodispersed polymer/polydiacetylene nanocrystal composite particles.

Monodispersed polymer/polydiacetylenecomposite particles were synthesized by soap-free seeded emulsion polymerization of styrene andmethyl methacrylate; the products were characterized by XRD, SEM, TEM, UV-visible spectroscopy, and single particle scattering spectroscopy. In the synthesis process, polydiacetylene nanocrystals were found to act as inhibitor, and consequently a relatively low concentration was necessary. Different monomers lead to the differences in reaction condition and particle morphology; the PMMA composite particles were simpler in preparation than polystyrene particles, but the latter havebetter spherical morphology. The composite particles were composed of polymer shells and polydiacetylene cores, which kept their crystal structure and optical properties. A high percentage of cored particles could be achieved with optimized reaction conditions where the amount of seed was sufficient and the oily oligomer by-product was suppressed.

Monodispersed quinacridone nanocrystals prepared by a high-temperature and high-pressure liquid crystallization method.

Monodispersed quinacridone nanocrystals were fabricated by a high-temperature and high-pressure liquid crystallization method, which proved to be an advanced technique for fabricating nanocrystals of pigment compound. The aqueous dispersion liquid of quinacridone nanocrystals was very stable. The nanocrystats had a spherical shape with an average size of 60 nm when water was used as the high-temperature and high-pressure liquid at 260 degrees C and cooling solvent. The crystal structure of the nanocrystals could be controlled by varying the experimental conditions.

Single-crystal-to-single-crystal transformation of diolefin derivatives in nanocrystals.

Topochemical [2 + 2] cycloaddition polymerization of methyl p-phenylenediacrylate and 2,5-distyrylpyridine in nanocrystals, prepared by the reprecipitation method, were investigated in comparison with those in bulk crystals. The bulk single crystals, larger than 1 mum in size, broke into microcrystals with variety of size and shape in the course of polymerization. Interestingly, however, these nanocrystals show single-crystal-to-single-crystal transformation.