Polythiophene photoexcitation

Analysis of the spin-1/2 2-PADMR spectrum is more complicated as it contains two features with increased and decreased transmission. As the photoexcitation density is proportional to -AT, we describe these as PA-quenching (Sn<0) and PA-enhancing (Sn >0) bands. We defer detailed discussion of the spectrum to the following section, where we compare the doping, PA, and PADMR studies of a-sexithiophene (u-6T) and polythiophene. Magnetic resonance is found to enhance... 

There are two types of photopolymerization processes (1) photopolymerization with photocatalytic systems and (2) direct photoexcitation of the monomer. The former has been demonstrated by the formation of polythiophene and polypyrrole either by n-type... 

Photoinduced infrared absorption studies show that the photoinduced infixired modes are much weaker in intensity, than the photoinduced electronic transition [23], in contrast to the behavior of polyacetylene [51,52] and polythiophene [6]. Analysis, within the amplitude mode formalism [53], indicates that the polarons are massive, > or -60 m, while use of bond order [54] or Holstein [55] polaron formalisms leads to an even larger estimate of the mass of the polarons. Photoexcitation, into either the exciton peak or the 7C-to-7t peak of emeraldine base, produces essentially identical long-lived photoinduced infrared modes [29]. The long-lived photoinduced spectra of the leucoemeraldine base are much weaker. Similarly, the photoinduced infrared absorptions in the pemigraniline base are much weaker, than the photoinduced electronic transitions, again indicating massive photoinduced defects [30]. 

In this chapter we have reviewed the main cw techniques used to study photoexcitations in undoped conducting polymers. In particular, we have given an in-depth description, both experimental and theoretical, of the PM and ADMR techniques. We have used these techniques to study photoexcitations in two systems of conducting polymers—(r Aj, -(CH), with its unique twofold degeneracy and polythiophene, a representative of the NDGS polymers. We have identified long-lived charged and neutral photoexcitations in both systems and verified their spin states. We have also studied the relations between the various photoexcitations and the PL emission in these two polymer systems. 

Doping-Induced and Photoexcited Infrared Spectra of Oligo- and Polythiophenes... 

Because of such chemical and structural complexity, the verification of whether the DIIR spectra of doped polythiophenes show dispersion with CL is not easily carried out on doped samples. PlIR spectra of suitably photoexcited oligothiophenes and/or polythiophenes may provide some cleaner information. With this aim a large series of variously substituted oligo- and polythiophenes have been photoexcited and their PllR spectra recorded and analyzed [213]. 

The application to the case of the polymers of the bilayer heterojunction structure that has been used successfully with molecular semiconductors [139] has recently been reported. The fullerene ) provides a useful high electron affinity semiconductor, and it is found that blends of this with a range of soluble PPV and polythiophene derivatives show very efficient charge separation following photoexcitation [146-148]. Two-layer diodes of C60 and MEH-PPV were reported initially to show poor efficiencies [149], but photovoltaic efficiencies (short circuit) up to 9% have now been obtained for PPV/ Ceo diodes of the type shown in Fig. 29.20 [150]. Charac-... 

Usually the />-type doping predominantly occurs in the case of polythiophenes. Occasionally, however, does the -type doping take place for them [91]. A pair of charges both positive (hole) and negative (electron) can be introduced at once through photoexcitation [92]. Other special techniques of doping are presented in subsequent sections in connection with the properties of the charged states. 

Jiang X, Osterbacka R, Korovyanko O, An CP, Horovitz B, Janssen RAJ, Vardeny ZV (2002) Spectroscopic studies of photoexcitations in regiOTegular and regiorandom polythiophene films. Adv Fund Mater 12 587-597... 

Cmcial to photovoltaic apphcations, the first observation of a photoinduced charge transfer in double-cable polyfiillerenes was reported in 2000. Polymer 6, an electrochemically prepared polythiophene carrying fulleropyrrolidine moieties, was studied by means of different techniques, including steady-state photoexcited spectroscopy and light-induced electron spin resonance (Figure 8.5) [22, 23]. 

---