Four isomeric naphthodithiophenes (NDTs) with linear and angular shapes were introduced into the polythiophene semiconductor backbones, and their field-effect transistor performances were characterized. The polymers bearing naphtho[1,2-b:5,6-b']dithiophene (NDT3), an angular-shaped NDT, exhibited the highest mobilities of ∼0.8 cm(2) V(-1) s(-1) among the four NDT-based polymers, which is among the highest reported so far for semiconducting polymers. Interestingly, the trend of the mobility in the NDT-based polymers was contrary to our expectations; the polymers with angular NDTs showed higher mobilities than those with linear NDTs despite the fact that naphtho[2,3-b:6,7-b']dithiophene (NDT1), a linear-shaped NDT, has shown the highest mobility in small-molecule systems. X-ray diffraction studies revealed that angular-NDT-based polymers gave the highly ordered structures with a very close π-stacking distance of 3.6 Å, whereas linear-NDT-based polymers had a very weak or no π-stacking order, which is quite consistent with the trend of the mobility. The nature of such ordering structures can be well understood by considering their molecular shapes. In fact, a linear NDT (NDT1) provides angular backbones and an angular NDT (NDT3) provides a pseudostraight backbone, the latter of which can pack into the highly ordered structure and thus facilitate the charge carrier transport. In addition to the ordering structure, the electronic structures seem to correlate with the carrier transport property. MO calculations, supported by the measurement of ionization potentials, suggested that, while the HOMOs are relatively localized within the NDT cores in the linear-NDT-based polymers, those are apparently delocalized along the backbone in the angular-NDT-based polymers. The latter should promote the efficient HOMO overlaps between the polymer backbones that are the main paths of the charge carrier transport, which also agrees with the trend of the mobility. With these results, we conclude that angular NDTs, in particular NDT3, are promising cores for high-performance semiconducting polymers. We thus propose that both the molecular shapes and the electronic structures are important factors to be considered when designing high performance semiconducting polymers.
We have designed and synthesized novel semiconducting polymers by introducing naphtho[1,2-b:5,6-b']dithiophene (NDT) into the polythiophene backbone. These polymers, which have a highly pi-extended heteroarene unit, achieved mobilities (>0.5 cm(2) V(-1) s(-1)) that are among the highest recorded to date for semiconducting polymers and most probably result from the highly ordered thin-film structures with crystalline close pi stacking. It is noteworthy that the choice of isomeric heteroarenes in the unit can dramatically change the physical and electronic structures and hence the OFET performance of the semiconducting polymers, even though the two isomers possess similar electronic structures; interestingly, this contrasts with the trend in small-molecule systems. We believe that these findings will give new insight into the design of new organic semiconducting materials and that the present polymers are promising materials for printable electronics.
We report the synthesis, characterization, and OFET and OPV properties of a series of novel naphthodithiophene (NDT3)-based donor− acceptor semiconducting polymers. A striking feature of the present polymers is the very close π−π stacking of 3.5 Å, most likely as a result of the large π system and the D−A system in the polymer backbone. PNDT3NTz-DT, in particular, is found to be one of the few examples of versatile polymers that exhibit both the field-effect mobility of ∼0.5 cm 2 /(V s) and the PCE of ∼5%. These results indicate that NDT3 is a promising versatile core unit for semiconducting polymers and that the use of highly π-extended heteroarenes as both the donor and the acceptor unit is a promising design strategy to develop high performance polymers.
Adlayers of cobalt(II) porphine (CoP) and [2,3,7,8,12,13,17,18-octaethyl-21H,23-H-porphine]cobalt(II)
(CoOEP) were formed on Au(111) by immersing the substrate in a benzene solution containing either CoP
or CoOEP molecules and investigated in 0.1 M HClO4 by using in situ scanning tunneling microscopy. Highly
ordered arrays of CoP were observed on the Au(111)-(1×1) surface under controlled potential conditions.
The adlayer of CoOEP molecules was also highly ordered, whereas the Au(111) substrate was found to
become reconstructed upon adsorption of CoOEP. Both CoP and CoOEP molecules were closely packed on
Au(111). On the adlayers of CoP and CoOEP, the electrochemical reduction of O2 was examined in 0.1 M
HClO4 saturated with O2. The adlayers of both CoP and CoOEP on Au(111) enhanced the reduction of O2.
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