Poly emission colors

Fig. 9 (a) Molecular structures of novel ESIPT dyes, 2,5,-bis[5-(4-t-butylphenyl)-[l,3,4]oxadia-zol-2-yl]-phenol (SOX), and 2,5-bis[5-(4-t-butylphenyl)-[l,3,4]oxadiazol-2-yl]-benzene-l,4,-diol (DOX). (b) Emission colors in the Commission Internationale de L Eclariage (CEE) chromaticity diagram. The inner oval and the filled circle at coordinate (x,y) of (0.33, 0.33) indicate the white region and the ideal color, respectively. Note that PS and PVK denote polystyrene and poly (N-vinylcarbazole) film (reprint from ref. [91], Copyright 2005 Wiley-VCH)... 

The emission color of PAVs depends crucially on the nature of the arylene unit. Replacement of a phenylene with an oligophenylene unit produces a blue-shift in the emission, e. g. the poly(pentaphenylene vinylene) 58 is a blue emitter (2rnax = 446 nm) [71], while heterocydes induce red-shifts. This is particularly marked in the case of thiophene so that the polymer 59 actually emits in the near-infrared (7m lx = 740 nm) [72]. The picture with fused polycyclic aromatics is more complicated with the 1,4-naphthalene 19 [73] and 9,10-anthracene 60 [74] polymers both being markedly red-shifted in emission compared with PPV (1), while the 2,6-napthalene 18 [75] and 3,6-phenanthrene 61 [58] materials are slightly blue-shifted. 

By contrast electron-rich heteroaromatic units such as 2,5-pyridines or 2,5-thiophenes provide a way to redshift the emission of PAVs (Figure 4.5). The lower symmetry of the pyridine than the phenylene ring means that poly(pyridine vinylene) can be produced as a random polymer or in two regioregular forms—head-to-tail (35) and head-to-head (36) [74]. The EL emission maxima of these appear at 575, 584, and 605 nm, respectively. The thiophene-containing copolymer 37 has even more redshifted emission (Amax = 620 nm) [107,108]. The most redshifted emission yet to be reported from PAV is near-infrared emission (Amax = 800 nm) from the polymers 38 (Amax = 740 nm) [109] and 39 (Amax=800 ntn) [110,111]. A wide range of other heteroaromatic units have been incorporated into PAVs with emission colors ranging from green to red. 

Bithiophene and a-terthiophene monomers containing jS-aryl substituents have also been polymerized. A material derived from XL has been used in blends with other poly(3-substituted thiophene)s to afford electroluminescent devices whose emission color depended on the applied voltage [62]. Monomers in which the central ring of a-terlhiophene has been substituted with phenyl-157,63], p-cyanophenyl-, p-methoxyphenyl-, p-pyridyl-, 2-thienyl-, or 3-methyl-2-thienyl [63] have been electro-chemically oxidized to yield mixtures of oligomers in all cases [63]. 

For two series of rod-coil copolymers [95] poly(l,4-phenylenebenzobisthi-azole-co-decamethylenebenzobisthiazole) (see Fig. 29b) and poly[(l,4-phen-ylenedivinylene)benzobisthiazole-co-decamethylenebenzobisthiazole] (see Fig. 29c) the authors also investigated the photophysical properties with varying composition. In these cases the photoluminescence quantum yield reached over seven fold higher values than for a pure conjugated homo polymer. Furthermore the emission color was tunable in the visible region by varying rod fraction. 

Derivatives of P(PV) continue to be the targets of choice for tailoring of LED emission color. For example, Yin et al. [769] described a unique derivative, poly(2,5-diphenyl-l,3,4-oxadiazolyl)-4,4 vinylene) (structure in Eflj 16J below), with a peak emission at 483 nm and a turn on voltage of 6 V in an ITO/CP/Al configuration. 

Poly(p-phenyleneethynylene)-fllt-pol)r(p-phenylenevinylene)s (PPE-PPVs) with a variation in their alkoxy side chains are attractive materials due to their tunable band gap properties and thus variable emission color. They also proved to be promising electron donor materials in solar cell applications. Alkoxy chains, grafted as side groups on the... 

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