Synthesis of Novel Poly[(2,5-dimethoxy-p-phenylene)vinylene] Precursors Having Two Eliminatable Groups: An Approach for the Control of Conjugation Length

Synthesis of Poly(arylenevinylene)s by Rhodium-Catalyzed Stitching Polymerization/Alkene Isomerization

Poly(arylenevinylene)s constitute an important class of π-conjugated polymers for their potential utility as optoelectronic materials. Herein, we developed a sequence of rhodium-catalyzed stitching polymerization of 1,2-dialkynyl(hetero)arenes and aromatization-driven alkene isomerization for the synthesis of new poly(arylenevinylene)s. The polymerization and subsequent alkene isomerization proceeded smoothly with high degree of stitching efficiency by employing a Rh/tfb complex as the catalyst, and not only diynes but also triynes and tetraynes could be polymerized to give poly(arylenevinylene)s that are not easily accessible by existing synthetic methods. The polymers obtained by the present method were thermally stable, and their optical properties could be varied depending on the repeating unit structure.

Fluorescence development of fingerprints by combining conjugated polymer nanoparticles with cyanoacrylate fuming

Selecting appropriate developing methods/reagents or their combination to enhance the effect for fingerprint development is of great significance for practical forensic investigation. Ethyl-2-cyanoacrylate ester (superglue) fuming is a popular method for "in-situ" developing fingerprints in forensic science, followed by fluorescence staining to enhance the contrast of the fingerprint image in some occasion. In this study, a series of fluorescent poly(p-phenylene vinylene) (PPV) nanoparticles (NPs) in colloidal solution were successfully prepared and the emission color was tuned via a simple way. The fuming process was carried out using a home-made device. The staining was accomplished by immersing a piece of absorbent cotton into the solution of NPs, and then gently applied on the fumed fingerprints for several times. The PPV NPs were found to have a better developing effect than Rhodamine 6G when excited by 365 nm UV lamp. Different emission colors of NPs are advantageous in developing fingerprints on various substrates. Mechanism study suggested that the NPs were embedded in the porous structure of the superglue resin. In all, the combination of fuming method with the staining by conjugated polymer NPs has been demonstrated to be successful for fluorescent fingerprint development and be promising for more practical forensic applications.

Color Tuning of Core-Shell Fluorescent Microspheres by Controlling the Conjugation of Poly(p-phenylenevinylene) Backbone

A series of poly(p-phenylenevinylene) (PPV)-coated microspheres with varied fluorescent emission colors have been prepared by controlling the average length of the conjugated segments on the polymer backbone. A modified Wessling method was used for preparing PPV with different conjugation segments. The labile sulfonium groups of the initial polymer precursor of PPV (pre-PPV) were partly substituted by relatively stable methoxyl groups. A series of precursors with different degrees of substitution were prepared by controlling the time of reaction; these precursors were adsorbed onto the negatively charged substrate spheres. Subsequently, heterogeneous thermal treatment eliminated the sulfonium groups selectively to form the conjugated segments on the PPV backbone with varied average conjugation lengths. Under UV exposure, the as-prepared PPV-coated microspheres displayed emission colors ranging from blue to green; a 65 nm shift in the emission maximum was observed in the fluorescence spectra. The gradual color change in emission of spheres was also confirmed in a confocal microscopy study. Further characterizations indicated that these microspheres possessed clear core-shell structure, good monodispersity in size, smooth surfaces, uniform emission, and superior thermal and photo stability. Flow cytometry measurements indicated that these spheres have very different patterns of intensity combination from four-signal receiving channels. The simple method reported herein, which can effectively and efficiently tune the emission color of the fluorescent microspheres, is a promising approach for preparation of microspheres used as encoded signal carrier in flow cytometry and other high-throughput techniques.

Realization of fluorescence color tuning for poly(p-phenylenevinylene) coated microspheres via a heterogeneous catalytic thermal elimination process

Fluorescent microspheres with clear core–shell structures and various emission colors were successfully prepared via a catalytic elimination process.

New Blue-Photoluminescent Semi-Conducting Polymer Derived from Fluorinated Bisphenol A

A new confined p-phenylenevinylene (PPV)-type polymer (BPAF-PPV ) has been synthesized using Wittig condensation. The chemical structure of the polymer was well defined by 1H-NMR, 13C-NMR, and FT-IR spectroscopic analysis. BPAF-PPV contains oligomeric PPV units separated by hexafluoroisopropylidene groups in the main chain; it is fully soluble in common organic solvents and has a number-average molecular weight of 4570 g mol-1. Differential scanning calorimetry indicates that BPAF-PPV is amorphous and displays a glass transition temperature of 114 °C. The optical properties of the polymer were investigated by UV-visible absorption and photoluminescence spectroscopies. Its thin film showed a blue photoluminescence with a narrow emission spectrum. A high photoluminescence quantum efficiency of about 83% was determined in dilute solution. From the cyclic voltammetry analysis, the electrochemical bandgap was estimated to be 3.08 eV. A single-layer diode device of the configuration indium-tin oxide/ BPAF-PPV/aluminium has been fabricated and has a relatively low turn-on voltage of 3.0 V.

Well-Packed Chains and Aggregates in the Emission Mechanism of Conjugated Polymers

We synthesized dialkoxy-substituted poly[phenylene vinylene]s (dROPPV-1/1, 0.2/1, and 0/1) consisting of two repeating units with different side-chain lengths (methoxy and 3,7-dimethyloctyloxy). These polymers can serve as a model system to clarify roles of aggregates (the sites with ground-state interchain interactions) and the independent chain segments in the well-packed chains (the chain segments that are compactly packed without interaction) in the emission mechanism of conjugated polymers. Due to the packing of polymer chains, films of all of these polymers are accessible to interchain excitations, after which excitons can re-form to result in delayed luminescence. Besides, some chains form aggregates so that the delayed luminescence is no more the ordinary single-chain emission but red-shifted and less structured. Not only the re-formation of these indirect excitons but also the aggregation of chains are facilitated in the polymers with short methoxy side groups, revealing that both packing and aggregation of chain segments require a short spacing between polymer chains. However, the incorporation of other side chains such as the 3,7-dimethyloctyloxy group to dROPPVs is necessary for the formation of aggregates because these long branched side chains can reduce the intrachain order imposed by the short methoxy groups, which accounts for the absence of aggregate emission in the well-studied poly[2,5-dimethoxy-1,4-phenylene vinylene]. This study reveals that the well-packed chains do not necessarily form aggregates. We also show that the photophysical properties and the film morphology of conjugated polymers can be deliberately controlled by fine-tuning of the copolymer compositions, without altering the optical properties of single polymer chains (e.g., as in dilute solutions).