Thiophene-Based Semiconductors

Since this ordering can be valid over several monolayers, in thin films the layers can be seen as two-dimensional mediums. Charge transport in these mediums is favoured in the direction parallel to the organic layer, which was again shown by Horowitz and Gamier [33] with X-ray diflxaction measure- 

unsubstituted a-nT is a model system used in recent literature. One disadvantage towards application of the unsubstituted oligothiophenes however is the poor solubility of the rigid rods [34]. 

---

Ando et al. used trifiuoromethylphenyl end groups in conjunction with thiophene and thiazolothiazole to realize n-channel thiophene-based semiconductors for OFETs. Electron mobilities for the oligomer 62 (Figure 16.30) were found to be as high as 0.30 cm V s with an /on 7off of 10 [126]. A... 

It is also possible to produce covalently bonded alkyl MLs on Si(l 11) surfaces using a variety of chemical reactions with passivated H-terminated Si(l 11), but the preparation methods are more complex than the immersion strategy in part due to the higher reactivity of silicon. This is a major achievement because it allows direct coupling between organic and bio-organic materials and silicon-based semiconductors. Both pyrolysis of diacyl peroxides (Linford Chidsey, 1993) and Lewis acid-catalyzed hydrosilylation of alkenes and direct reaction of alkylmagnesium bromide (Boukherroub et al, 1999) on freshly prepared Si(lll)-H produce surfaces with similar characterishcs. These surfaces are chemically stable and can be stored for several weeks without measurable deterioration. Thienyl MLs covalently bonded to Si(l 11) surfaces have also been obtained, in which a Si(l 11)-H surface becomes brominated, Si(lll)-Br, and is further reacted with lithiated thiophenes (He etal, 1998). 

Design, Synthesis, and Transistor Performance of Organic Semiconductors 199 Thiophene-based N-Channel Oligomers (49a-49q)... 

A series of naphthodithieno[3,2-l)]thiophene-based (NNTT) semiconductors were synthesized (140CF333) and their optical and electrochemical properties characterized. As shown, the first important step involves a palladium-catalyzed Suzuki of the thiopheneboronic acid. Subsequent FeCl3-catalyzed oxidative cyclization affords desired NDTT derivatives. 

Thiophene-Based Conjugated Systems as Organic Semiconductors for Field-Effect Transistors... 

The synthetic chemistry of thiophene-based organic semiconductors develops essentially along two main lines namely (1) processible materials that are mostly based on polymeric structures and (2) short-chain oligomers used either as single crystals or as polycrystalline films prepared by thermal evaporation under vacuum. Although this latter class of materials has given rise to much development during the last two decades, only polymeric materials will be considered here. 

Very recently, Sasaki et al. fabricated a microring laser by making the most of the various semiconductor processing methods, and achieved low-threshold laser oscillation [51]. This demonstrates the robustness of thiophene-based oligomers and that these materials are compatible with semiconductor processing. 

The cyclic voltammetry measurements of both polymers in thin films showed that IIDDT owned HOMO/LUMO level of -5.7/-3.7 eV, and IIDT had HOMO/ LUMO level of -5.8/-3.S eV. Both polymers showed much stronger oxidative peaks than their reductive peaks, and the oxidative peak of IIDDT seems more reversible than that of IIDT (Tig. 2.2c). This result is consistent with the device performance that both the polymers are typical p-type semiconductors and IIDDT exhibited a better performance. Compared with traditional thiophene or fused thiophene based polymers, both polymers showed much deeper HOMO levels, which is attributed to the strong election-withdrawing ability of the isoindigo core. Computational results indicate that the HOMO of the polymers are well delocalized... 

The use of organic polymers as conductors and semiconductors in the electronics industry has led to a huge research effort in poly(thiophenes), with a focus on the modification of their electronic properties so that they can behave as both hole and electron conductors. Casado and co-workers [60] have performed combined experimental and theoretical research using Raman spectroscopy on a variety of fluorinated molecules based on oligomers of thiophene, an example of one is shown in Figure 7. 

---