Yamamoto method

FIGURE 12.5 Chemical routes for the formation of the two different PPP on the basis of the Kovacic and Yamamoto methods. (Adapted from Endo, M., et al., Mol. Cryst. Liq. Cryst., 310, 353, 1998. With permission.)... 

The Yamamoto method can be used to synthesize fluorene homopolymers (Scheme 7.3A) as well as random alternating copolymers [52], Alternating copolymers can be synthesized through Suzuki coupling (Scheme 7.3B), which tolerates a wide variety of different functional groups [53],... 

Figure 16.39. Effect of AsFj doping and air exposure on the ESR spectrum of poly(p-phenylene) prepared by Yamamoto method. Adapted from J. Phys.D Appl. Phys. 28, I (1995), with permission of lOP Publishing Ltd.

Yamamoto and coworkers prepared a PPP derivative 14 by treatment of 1 (prepared by the Yamamoto method [54]) with perfluorpropylperoxide (Scheme 6). From NMR and other analysis they estimated that the average chain length was 13 benzene units with an average of two perfluorpropyl imits per molecule. This material showed blue PL (A-max = 450 nm), and was used to construct a device whose emission colour was found to shift from green to blue with increasing applied voltage [55]. 

The Yamamoto method of condensing dihalobenzenes 16 with nickel(O) (Scheme 9) has the advantage of experimental simplicity, but is limited to preparation of homopolymers and random copolymers, and requires stoichiometric amounts of expensive nickel(O) reagents. These can be generated in situ by the reduction of nickel(II) salts in the presence of suitable ligands. 

An exception is the bisimide 46 (Scheme 19), which shows green PL ( max = 553 nm) that is similar to that of the monomer, suggesting that the emission comes from isolated monomer units [106]. A soluble poly(mefa-phenylene) 47, made by Reddinger and Reynolds by the Yamamoto method, which has an even shorter conjugation length, emits mainly in the ultraviolet (A,max = 346 nm) [107]. Other mefa-hnked polymers 48, however, show violet-green PL (A,max = 445-532 nm) as the emission comes from the substituents [108]. 

Miller and coworkers have prepared copolymers 111 (Scheme 53) of di-hexylfluorene with anthracene by the Yamamoto method. These show stable blue emission (kmax = 455 nm) even after prolonged annealing [182,218]. As the ratio of anthracene (15%) to fluorene (85%) units was too low to produce significant steric repulsion between the polymer chains, they attributed the absence of long-wavelength emission to trapping of the exciton at the anthracene sites and subsequent emission therefrom [218,219]. Similar copolymers 112 with dioctylfluorene are reported to show PL and EL maxima at respectively 446 nm and 435 nm [220]. The reason for this difference is not apparent. 

Yamamoto Method. Yamamoto et al. [423] prepared polythiophene by treating 2,5-dibromothiophene with Mg and catalyzing the polymerization by Ni(bipyridine)2Cl2 (Fig. 15). A similar... 

Figure 3 shows the charge/discharge profiles for PPP-based carbon, which was heat-treated from 700 to 3000 °C. Two different PPPs have been used as precursors, and synthesized by the Kovacic- and Yamamoto-methods [20, 21]. PPP from the Kovacic method is prepared through a polymerizadon of benzene or of a... 

Fig. 3 Discharge (a, b) and Charge (c, d) curves of poly(para-phenylene)-based carbon, which was synthesize by Kovaeie-(a, c) and Yamamoto-method (b, d) as a function of HTT...

The use of lichen tissue cultures and the development of lichen thalli in vitro have been discussed by Japanese workers 741, 745, 759). The method for cultivating lichen tissue (Yamamoto method) is demonstrated in Fig. 11. The cultivated lichens and the corresponding references are summarized in Table 13. 

Fig. 11. Yamamoto method for cultivating lichen tissue References, pp. 239-276...

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