Well-defined novel fluorene-containing polymers: synthesis, fluorescent properties, and micellar nanoparticles.

We report the synthesis of a new monomer, 9,9-diethylfluoren-2-yl methyl methacrylate (FMMA) and its controlled reversible addition-fragmentation chain transfer (RAFT) homopolymerization to give PFMMA with narrow polydispersity indices (PDIs). The corresponding copolymerization with 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) also gave well-defined block and random copolymers with controlled molecular weights and narrow PDIs. Their thermal behavior, UV-Vis absorption, and photoluminescent properties were studied. The PDMAEMA-b-PFMMA amphiphilic block copolymers showed self-assembly into aqueous spherical micellar nanoparticles with uniform size. The PFMMA core showed photoluminescence when carrying dichloromethane "guest" molecules and its emission was shown to be quenched after the release of the guest.

Block copolymer-like self-assembly of fluorocarbon end-functionalized polystyrene and polybutylmethacrylate.

We demonstrate the self-assembly through fluorophilic interactions of a blend of perfluorocarbon (RF) end-functionalized polystyrene and the corresponding RF-polybutylmethacrylate into optically transparent materials that retain domain characteristics typical of the component polymers but show well-defined lamellar nanostructured morphologies that qualitatively resemble that of the corresponding block copolymers.

DFT based Monte Carlo simulations of poly(9,9-dialkylfluorene-2,7-diyl) polymers in solution.

The dilute solution properties of poly(9,9-dihexylfluorene-2,7-diyl) (PDHF) were studied by coupled SEC/light scattering and MALDI-TOF over a large molecular weight (MW) span ranging from PDHF oligomers (1-8-mer) to high MW polymer. The results were compared with Monte Carlo simulations based on realistic PDHF models obtained from X-ray data and density functional theory (DFT) calculations and with a DFT based Kratky-Porod-Benoit-Doty (KPBD) worm-like chain. The simulations called "selective random walk" (SRW) and the corresponding "selective self-avoiding random walk" (SSAW) explicitly take into account the rotationally labile bonds between the fluorene units in that four distinct torsion angles (+/-37.5 and +/-143 degrees) between the units are chosen randomly. The simulations better account than the KPBD model for the experimental data obtained by us and others for various poly(9,9-dialkylfluorene-2,7-diyl) polymers but still give somewhat larger values for the radii of gyration and hydrodynamic volumes. The torsion angle selectivity of the SRW and SSAW simulations predict long chain sections punctuated by sudden sharp loops.

Percutaneous fiber-optic sensor for chronic glucose monitoring in vivo.

We are developing a family of fiber-optic sensors called Sencils (sensory cilia), which are disposable, minimally invasive, and can provide in vivo monitoring of various analytes for several weeks. The key element is a percutaneous optical fiber that permits reliable spectroscopic measurement of chemical reactions in a nano-engineered polymeric matrix attached to the implanted end of the fiber. This paper describes its first application to measure interstitial glucose based on changes in fluorescence resonance energy transfer (FRET) between fluorophores bound to betacyclodextrin and Concanavalin A (Con A) in a polyethylene glycol (PEG) matrix. In vitro experiments demonstrate a rapid and precise relationship between the ratio of the two fluorescent emissions and concentration of glucose in saline for the physiological range of concentrations (0-500mg/dl) over seven weeks. Chronic animal implantation studies have demonstrated good biocompatibility and durability for clinical applications.

Investigation of macrocyclic polymers as artificial light harvesters: subpicosecond energy transfer in poly(9,9-dimethyl-2-vinylfluorene).

The spectroscopy and dynamics of a novel molecular architecture that mimics natural light harvesting have been characterized. The deployment of 9,9-dimethyl-2-fluorenyl (DMF) chromophores in atactic macrocyclic poly(9,9-dimethyl-2-vinylfluorene) is similar to that in the light harvesting antenna LH2 of the purple photosynthetic bacteria. A variety of spectroscopic probes are used to study the dynamics in these novel polymer systems. The number of chromophores is tuned from 12-142 identical chromophore units. Steady-state absorption and emission measurements, time-resolved fluorescence, and ultrafast transient absorption anisotropy techniques provide evidence for distinct differences in the photophysics of matching molecular weight linear and cyclic polymers and of the occurrence of energy transfer in these polymers. There is direct evidence of energy transfer in these macrocycles manifested in the depolarization decay components, which are characterized by two exponentials and are substantially faster than observed for reorientation of the free DMF chromophore. The time constants for the macrocycles are 700-900 fs and 7-8 ps and are size dependent; the biexponential decay arises from conformational and stereochemical disorder and can be well described by a master equation simulation assuming Förster incoherent hopping on model polymer structures. The results suggest energy hopping between adjacent chromophores on a 1 ps time scale. The pathway for energy migration is shown to be primarily between nearest neighbors along the cyclic backbone, but there is a considerable spread in the site-to-site hopping rates. Small cycles adopt a pseudoplanar ring type arrangement of the chromophore transition dipoles as observed in bacterial light harvesting antenna, and it is found that the linear polymers also show similar short-range planarity of transition dipoles. Overall, it is found that such small macrocyclic polymers possess excellent characteristics for light harvesting among identical chromophores and behave as a circular photonic wire.

Senciltrade mark project: development of a percutaneous optical biosensor.

We describe the design, fabrication method, biocompatibility test results, and first application of the novel chemical sensor technology that is under development. The sensor is designed to be minimally invasive, disposable and easily readable to make frequent measurements of various analytes in vivo over a period of 1-3 months. It uses photonic sensing of a chemical reaction that occurs in a polymer matrix bound to the internal end of a chronically implanted percutaneous optical fiber.

Phosphorescence quenching by conjugated polymers.

Energy transfer between phosphors and conjugated polymers was investigated using a fluorene trimer (F3) as a model conjugated material. The phosphors studied were bis-cyclometalated iridium complexes (FP, PPY, BT, PQ, and BTP), with triplet energies of 2.6, 2.4, 2.2, 2.1, and 2.0 eV, respectively (based on phosphorescence spectra). Stern-Volmer analysis of luminescent quenching shows that energy transfer from either FP or PPY to F3 is an exothermic process with Stern-Volmer quenching constants (kqSV) of near 109 M-1 s-1 while energy transfer from BT, PQ, and BTP is endothermic (kqSV = 107-106 M-1 s-1). On the the basis of above results, the triplet energy of F3 is estimated to be less than 2.3 eV (530 nm). This study suggests that conjugated polymers, which typically have lower T1 energies than F3, should also quench phosphorescent emission in thin films and organic light-emitting diodes (OLEDs) incorporating these and related phosphorescent dopants.