Energy transfer copolymer

Highly efficient green photoluminescence has also been realized from SCPs. Copolymers 11 (Fig. 5) derived from 2,7-fluorene and 2,3,4,5-tetraphenylsilole show absolute PL quantum yields up to 84%.28 A well-defined alternating copolymer 12 with a repeating unit made up of ter-(2,7-fluorene) and 2,5-silole possesses an absolute PL quantum yield >80%.29 SCPs 13 with a main chain structure of 3,6-carbazole-2,7-fluorene-2,5-silole also show absolute PL quantum yields up to 86%.30 An energy transfer copolymer 14 of 2,7-dibenzosilole and... 

Characterization and control of interfaces in the incompatible polymer blends were reported by Fayt et al. [23]. They used techniques such as electron microscopy, thermal transition analysis, and nonradiative energy transfer (NRET), etc. They have illustrated the exciting potentialities offered by diblock copolymers in high-performance polymer blends. 

The observed luminescence properties of the copolymer yarns can be easily explained if an energy transfer mechanism is assumed to be operating (Figure 7). Triplet-triplet energy transfer from the terephthalate units to the 4,4 -biphenyl -dicarboxyl ate units explains both the dual fluorescent/phospho-rescent emissions from the 4,4 -biphenyldicarboxyl ate units as well as the quenched phosphorescence from the terephthalate units. 

Microanalysis of the three PET-4,4 -SD copolymer yarns for sulfur yielded concentrations in agreement with the theoretical values. Since the 4,4 -SD comonomer was definitely incorporated into the three copolymer yarns, the absorption and luminescence characteristics of the copolymers point towards a co-absorption process between 4,4 -SD and PET rather than an electronic energy transfer process. 

Pei et al. [412] reported an alternating fluorene copolymer 331 with 2,2 -bipyridyl in a side chain that emitted at 422 nm. Treating this polymer with Eu3+ chelates formed the polymeric complexes 332-334. Their emission was governed by intramolecular Forster energy transfer, whose efficiency depends on the structure of the ligands and the Eu3+ content (Scheme 2.49) [412], The most effective energy transfer manifested itself in a single red emission band at 612 nm for the complex 332 with a maximum intensity achieved at —25 mol% content of Eu3+. 

Another example of efficient Forster energy transfer in Eu3+ complexes of fluorene copolymers (similar to the alternating copolymers described in Scheme 2.49) was demonstrated by Huang and coworkers [414] for random copolymers. They synthesized copolymers 336 with a different ratio between the fluorene and the benzene units in the backbone and converted them into europium complexes 337 (Scheme 2.50) [414]. The complexes 337 were capable of both blue and red emission under UV excitation. In solution, blue emission was the dominant mode. However, the blue emission was significantly reduced or completely suppressed in the solid state and nearly monochromatic (fwhm 4 nm) red emission at 613 nm was observed. 

It is interesting that statistical copolymers 343, containing m-phenylene linkages that are supposed to interrupt conjugation, showed a PL maximum of 475 nm, similar to 342. Due to efficient energy transfer from the meta- to the para-linked chromophores, the emission maxima did not depend on the ratio of m- and p-divinylbenzenes, unless 100% loading of the meta units was used [420] (Scheme 2.54). 

When an electron-deficient BT unit was incorporated into the backbone of these polymers, an efficient energy transfer resulted in complete fluorescence quenching from the fluorene sites already at BT concentrations as low as 1% (for both neutral and quaternized copolymers, 377 and 378) [440] (Chart 2.93). These macromolecules emit green (544-550 nm, 377) to yellow (555-580 nm, 378) light and can be processed from environment-friendly solvents such as alcohols. The PLED fabricated with these polymers showed high 4>(]over 3 and 1% for 377 and 378, respectively (A1 cathode). 

The nanoreplication of functional nanostructures has also been achieved through other block copolymer-templated structures. De Boer et al. [35] applied honeycomb-structured films of rod-coil block copolymer as patterned templates to replicate hexagonally packed arrays of aluminum cups on the substrate surfaces (Fig. 10b). Nguyen et al. [237] embedded semiconducting polymers in the channels of oriented hexagonal nanoporous silica and used this nanoscale architecture to control the energy transfer for potential optoelectronic applications. 

An energy transfer immunosensor described for IgG measurement exploits controlled release of donor and acceptor from ethylene-vinyl acetate copolymer plugs positioned in opposite ends of a cylindrical reaction chamber (Figure 14.19).(122) Fluorescein-antibody donor and Texas Red-antigen-IgG acceptor are continuously released from the polymeric plugs. The reagents diffuse to the center of the cylindrical reaction chamber, where a perpendicular top-mounted optical fiber delivers the excit-... 

Copolymers 15 (Fig. 6) derived from 2,7-fluorene and 2,5-dithienylsilole show red fluorescence via an energy transfer process.31 The APl could be 591 nm for copolymers with higher contents of 2,5-dithienylsilole. The absolute PL quantum yields (<30%) of the copolymers are somewhat lower than the green fluorescent SCPs. A copolymer 16 derived from 2,7-dibenzosilole and 4,7-dithienyl-2,l,3-benzothiadiazole show a better red fluorescence.26 The APL of the copolymer is at 629 nm, with an absolute PL quantum yield of 53%. 

The aggregation of the PMPS-PEO copolymers in solution and dispersion was fnrthered probed nsing flnorescence spectroscopy. A small red shift in the flnorescent emission maximnm was observed on increasing the water content, attributable to more effective energy transfer from shorter to longer PMPS segments. This indicated... 

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