Silicon-backbone cyclic and linear oligomers and high molecular weight linear polymers, poly(organosilylenes), have unique properties that distinguish them from saturated carbon polymer analogues. First, they behave as polyconjugated or even aromatic hydrocarbons' in that they undergo one-electron oxidation to cation radicals and exhibit low ionization p~t e n t i a l s ,~-~ one-electron reduction by alkali metals to anion-radi~als,~ and form u -+ T charge transfer complexes with strong electron acceptors such as tetracyanoethylene (TCNE).69 Second, both linear and cyclic poly(organosily1enes) are characterized by substantial delocalization of charges over the u -Si-Si-chain bonds, as demonstrated by the dependence of ionization p~t e n t i a l ,~ electron a f f i n i t~,~ and peak absorption wavelength',' on the number of silicon atoms in the chain, and by the ESR study of the cation radicals2 and anion radicals5 of polycyclosilylenes. Third, photoconductivity has been reported in poly(methylphenylsilylene) and its complex with 2,4,7-trinitro-9-fluorenone (TNF)."In this paper we report on another interesting property of this class of polymers, hole injection from photoelectrodes, and hole transport. Surprisingly, polymers with exclusively u -Si-Si bonds can support substantial hole transport, as demonstrated by our preliminary data on films of several homopolymers and copolymers, of the following general structure:where R is an aliphatic or an aromatic group.Hole drift mobilities a t different electric fields and various temperatures were measured by the standard current-mode time-of-flight method. The experimental arrangement for the time-of-flight measurements is shown in Figure 1. Figure l a depicts the device which consists of an aluminum electrode, a vapor-deposited -0.5 pm thick layer of amorphous selenium, a thicker, (10-20 pm) layer of polysilylene solvent coated from THF or toluene, and a semitransparent gold counter-electrode, approximately 100 A thick. The device is charged capacitatively (with gold as cathode) in the darkness to 104-105 V/cm and then exposed to a 510-nm laser light pulse. The light is transmitted through the cathode and polysilylene and is absorbed in the

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