Electron-accepting polymers

Electron donating polymers Electron accepting polymers 381-386 592... 

The importance of charge-transfer complexes (C-T complexes), most of them being composed of small molecule-small molecule or small molecule-macromolecule, has been pointed out in various fields, e.g. photochemistry487, electrochemistry488 and biochemistry489. Hie systematization of the procedures for the preparation of C-T complexes in low molecular weight compound systems has also been reported. However, there are only few studies on C-T complexes in intermacromolecular complex systems available, because electron-accepting polymers are difficult to synthesize. 

First, Sulzberg et al.381,382 studied the synthesis of high molecular weight electron-accepting polymers and their C-T complexes with electron-donating... 

Tazuke et al.592) reported the intermacromolecular C-T complex of a polyester bearing pendant carbazolyl groups (electron-donating polymer) with polyurethanes bearing pendant trinitrofluorenonyl groups (electron-accepting polymer). 

To develop further C-T complexes composed of macromolecules, it is necessary to synthesize new electron-accepting polymers with good physical and chemical properties but up to now, only a few syntheses of such polymers have been reported490-494). C-T complexes offer new application possibilities of polymers as high-conductive, heat-resistant, energy-transferrable, and charge-separable materials. 

In typical experiments, thin ( 100 nm) films of polymer blends were deposited by spin coating from a solution of the two polymers. Alternatively, two thin films of a hole-accepting and an electron-accepting polymer that had been deposited on ITO or metal substrates were laminated together in a controlled annealing pro-... 

Finally an electron-accepting polymer can be blended with a PAV to enhance its photoresponse. Here cyano-substituted PPVs such as 50 have been used successfully. Thus, in 1995, it was reported by the groups of Friend and Heeger that blends of MEH-PPV with CN-PPV (50) [211], or with MEH-CN-PPV (Figure 4.10, 61) [212] produce photocurrents with efficiencies up to 0.9%. However, despite further research efforts [213-217], the efficiency of devices using blends of PAVs with cyano-containing PPV... 

FIGURE 4.10 Electron-accepting polymers for use in PAV-based polymer-polymer bulk heterojunction solar cells. 

Charge transfer complexes are formed in systems of electron-accepting polymers and electron-donating polymers through charge-transfer interaction [54-57]. Charge-transfer complexes are mainly characterized by their ultraviolet and visible spectra. The ratio of their repeating units is almost unity. 

Using CPR, Burn and coworkers introduced several electron-accepting moieties such as p-nitrostyryl (69 [125]) and methylsulfonyl-phenyl (70 [126]) groups as substituents in the PPV backbone. However, essentially no difference in EL performance (maximum QE 0.01% for ITO/polymer/Al) was found between polymers 70 and 71 and the authors concluded that the methylsulfonyl group in the pendant phenyl ring does not facilitate electron injection (Chart 2.13). 

M. Jang, S. Song, and H. Shim, Efficient green light-emitting polymer by balanced injection of electron and holes new electron accepting perfluorinated substituent, Polymer, 41 5675-5679, 2000. 

J. Jacob, S. Sax, T. Piok, E.J.W. List, A.C. Grimsdale, and K. Mullen, Ladder-type pentapheny-lenes and their polymers efficient blue-light emitters and electron-accepting materials via a common intermediate, J. Am. Chem. Soc., 126 6987-6995, 2004. 

The electronic properties of n-conjugated polymers reflect well the basic electron-withdrawing or electron-donating properties of the components of the Ti-conjugated polymer [62]. In view of the electrochemical reduction potential, the thiophene unit and tetrathiafulvalene unit (Nos. 8 and 9 in Table 1) have a similar electronic effect in PAEs. It is reported that poly(arylenevinylene)s are also susceptible to electrochemical reduction [63, 64]. Due to the electron-accepting properties, PAEs are usually inert in electrochemical and chemical (e.g.,by I2 [54]) oxidation. 

One of the most promising uses of C60 involves its potential application, when mixed with 7r-conjligated polymers, in polymer solar cells. Most often the so-called bulk heterojunction configuration is used, in which the active layer consists of a blend of electron-donating materials, for example, p-type conjugated polymers, and an electron-accepting material (n-type), such as (6,6)-phenyl-Cgi -butyric acid methyl ester (PCBM, Scheme 9.6).38... 

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