Poly band gap

Wienk MM, Tm-biez MGR, Struijk MP, Fonrodona M, Janssen RAJ (2006) Low-band gap poly(di-2-thienylthienopyrazine) fullerene solar cells. Appl Phys Lett 88 153511... 

A small band gap poly(thienylene vinylene) macro-initiator 9 has been synthesized by Homer-Wadsworth-Emmons condensation. Rod-coil copolymers 10 have been obtained from it (Figure 7) they present red-shifted absorption spectra, which is very suitable for photovoltaic applications. 

Chen, W.-C., et al. 2004. Theoretical and experimental characterization of small band gap poly(3,4-ethylenedioxythiophene methinejs. Macromolecules 37 5959. 

JIA 09] Jiang H., Zhao X., Shelton A.H. et al., Variable-band-gap poly(arylene ethynylene) conjugated polyelectrolytes adsorbed on nanociystalline Ti02 photocunent efficiency as a function of the band gap"", ACS Applied Materials Interfaces, vol. 1, no. 2, pp. 381-387,2009. 

In two 1995 papers Chen and Jenekhe [130,131] describe the synthesis of poly(heteroarylene-methylenes), which are precursor polymers, and then the syntheses of a series of low band gap poly(heteroarylene methines) from these. Band gaps as low as 1.14 eV were observed for these polymers [4,129]. The first paper gives the synthesis of 20 new methylene-bridged polythiophenes of... 

When poly(thienylene vinylene) (66, R = H, band gap = 1.74 or 1.64 eV) [103,104] is substituted with alkoxy groups, it too shows considerably reduced band gaps. Poly(3-methoxythienylene vinylene) (66, R = OCH ) was reported to have an electrochemical band gap of 1.32 eV [105] and an optical band gap of 1.37 eV [104] poly(3-ethoxythienylene vinylene) (66, R = OC2Hs)was reported to have electrochemical and optical band gaps of 1.31 and 1.48 eV, respectively [104] and poly(3.4-dibutoxythienylene vinylene) (131) was reported to have a band gap of 1.62 eV [151],... 

Blouin, N., Michaud, A., Leclerc, M. A low-band gap poly(2,7-Carbazole) derivativefor use in high-performance solar cells. Adv. Mater. 19, 2295-2300 (2007)... 

Ajayaghosh, A. and J. Eldo. 2001. A novel approach toward low optical band gap poly-squaraines. Org Lett 3 (16) 2595-2598. 

The scope of Wessling route has been extended by Mullen and co-workers to develop a soluble precursor route to poly(anthrylene vinyiene)s (PAVs) [51]. It was anticipated that the energy differences between the quinoid and aromatic resonance structures would be diminished in PAV relative to PPV itself. An optical band gap of 2.12 eV was determined for 1,4-PAV 29, some 0.3 eV lower than the value observed in PPV. Interestingly, the 9, lO-b/.v-sulfonium salt does not polymerize, possibly due to stcric effects (Scheme 1-9). 

Polyacetylene is considered to be the prototypical low band-gap polymer, but its potential uses in device applications have been hampered by its sensitivity to both oxygen and moisture in its pristine and doped states. Poly(thienylene vinylene) 2 has been extensively studied because it shares many of the useful attributes of polyacetylene but shows considerably improved environmental stability. The low band gap of PTV and its derivatives lends itself to potential applications in both its pristine and highly conductive doped state. Furthermore, the vinylene spacers between thiophene units allow substitution on the thiophene ring without disrupting the conjugation along the polymer backbone. 

There have been very few examples of PTV derivatives substituted at the vinylene position. One example poly(2,5-thienylene-1,2-dimethoxy-ethenylene) 102 has been documented by Geise and co-workers and its synthesis is outlined in Scheme 1-32 [133]. Thiophene-2,5-dicarboxaldehyde 99 is polymerized using a benzoin condensation the polyacyloin precursor 100 was treated with base to obtain polydianion 101. Subsequent treatment with dimethyl sulfate affords 102, which is soluble in solvents such as chloroform, methanol, and DMF. The molar mass of the polymer obtained is rather low (M = 1010) and its band gap ( ,.=2.13 eV) is substantially blue-shifted relative to PTV itself. Despite the low effective conjugation, the material is reasonably conductive when doped with l2 (cr=0.4 S cm 1). 

S. Tasch, A. Niko, G. Leising, U. Scherf, Highly efficient electroluminescence of new wide band gap ladder-type poly(para-phenylenes), AppL Phys. Lett. 1996, 68, 1090. 

Polyfarylene vinylene)s form an important class of conducting polymers. Two representative examples of this class of materials will be discussed in some detail here. There are poly(l,4-phenylene vinylcne) (PPV) 1, poly(l,4-thienylene viny-lenc) (PTV) 2 and their derivatives. The polymers are conceptually similar PTV may be considered as a heterocyclic analog of PPV, but has a considerably lowci band gap and exhibits higher conductivities in both its doped and undoped stales. The semiconducting properties of PPV have been shown to be useful in the manufacture of electroluminescent devices, whereas the potential utility of PTV has yet to be fully exploited. This account will provide a review of synthetic approaches to arylene vinylene derivatives and will give details an how the structure of the materials relate to their performance in real devices. 

Zinc sulfide, with its wide band gap of 3.66 eV, has been considered as an excellent electroluminescent (EL) material. The electroluminescence of ZnS has been used as a probe for unraveling the energetics at the ZnS/electrolyte interface and for possible application to display devices. Fan and Bard [127] examined the effect of temperature on EL of Al-doped self-activated ZnS single crystals in a persulfate-butyronitrile solution, as well as the time-resolved photoluminescence (PL) of the compound. Further [128], they investigated the PL and EL from single-crystal Mn-doped ZnS (ZnS Mn) centered at 580 nm. The PL was quenched by surface modification with U-treated poly(vinylferrocene). The effect of pH and temperature on the EL of ZnS Mn in aqueous and butyronitrile solutions upon reduction of per-oxydisulfate ion was also studied. EL of polycrystalline chemical vapor deposited (CVD) ZnS doped with Al, Cu-Al, and Mn was also observed with peaks at 430, 475, and 565 nm, respectively. High EL efficiency, comparable to that of singlecrystal ZnS, was found for the doped CVD polycrystalline ZnS. In all cases, the EL efficiency was about 0.2-0.3%. 

The electronic band structure of a neutral polyacetylene is characterized by an empty band gap, like in other intrinsic semiconductors. Defect sites (solitons, polarons, bipolarons) can be regarded as electronic states within the band gap. The conduction in low-doped poly acetylene is attributed mainly to the transport of solitons within and between chains, as described by the intersoliton-hopping model (IHM) . Polarons and bipolarons are important charge carriers at higher doping levels and with polymers other than polyacetylene. 

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