Optical and Electrical Properties of Doped Polysilanes
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ABSTRACT The doping effects on optical and electrical properties of polysilanes have been investigated by in-situ measurement. An optical absorption associated with a-o'* transition was observed near 330 nm for polymnethylphenyisilane. By iodine doping, a new absorption was observed at the longer wavelength around 420 nm, which should originate from the charge transfer between dopant and a-conjugated system. Similar spectral changes have also been observed for most of investigated linear polysilanes. Furthermore, we have found drastic spectral change upon iodine doping into polysilane with p-N,N-diinethylaininophenyl substituent. It has very strong absorption up to 700 nm. It might originate from a strong interaction between the substituent and iodine. At the same time, a-conjugation might also play a significant role on doping into this system.
INTRODUCTION Highly ,r-conjugated polymers, such as polyacetylene, polythiophene and so on', have attracted much interest in both fundamental and practical viewpoints. These polymers demonstrate a semiconductor-metal transition on doping. The remarkable change of their properties associated with this transition is one reason why these polymers have become so attractive as functional polymers in practical applications. In the last few years, some ni-conjugated conducting polymers have been applied for batteries, capacitors, electrostatic shielding and so on. Recently, polysilanes2 have attracted great interest as a new class of linear ca-conjugated polymers. Since the first synthesis of soluble polysilane', intensive studies on polysilanes have been performed. As a result of studies on the properties of them, interesting electrical and optical properties have been found, for example the enhancement of electrical conductivity by doping 4 , photoconductivity and high hole mobilityS, large third-order non-linear susceptibility". Therefore, polysilanes are expected to be used as functional material in various fields. Doping into a-conjugated polymers is also very interesting as in the case of it-conjugated polymers. Jeyadev et al theoretically studied the polarons and bipolarons in linear polysilanes, and pointed out that they could be detected in photoexcited or doped states 7 . However, there have been only a few reports on doping into polysilanes. West et d reported an electical conductivity of AsF5 doped polysilane 4 and Qui et al only reported an absorption peak and electrical conductivity of doped polysilane substituted by fluoranthene groups", but they did not investigate any spectral change upon doping. In this paper, we will mainly report on the change in optical absorption spectra upon iodine doping by using in-situ measurement technique for the first time. And we will describe the peculiar spectral changes observed in polysilanes with p-N,N-dialkylamninophenyl group upon iodine doping. We will also discuss the spectral changes concerned with the charge transfer between polysilane and dopant. 267 Mat. Res. Soc. Symp. Proc. Vol. 328. ©1994 Materials Research Society
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