Carrier transport property of-conjugated dendrimer is of current scientific and technological interest because of a molecular architecture for organic semiconductor materials and because of a variety of practical applications such as light emitting diodes, thin film transistors, and photo-voltaic cells. 1-6 Previously, we reported the carrier transport property of the soluble-conjugated three-generation dendrimer which is composed of phenylene-vinylene as a dendron group and triphenylamine as a soluble surface group (G3D3-PV(TPA)) as shown in Figure 1b. 7 The carrier of transporting across the G3D3-PV(TPA) dendrimer film was preferentially hole with an indium-tin-oxide (ITO)/G3D3-PV(TPA)/Mg-Al cell. The Mg-Al is the opposite electrode composed of alloy of Mg and Al. The hole mobility was 10 À5 (cm 2 /(VÁs)) order at 25 C, which is the same order as that of poly(p-phenylene-vinylene) reported by Lebedev and co-workers though the dendrimer is surrounded by the triphenylamine surface group. 8 According to the results reported previously, the triphenylamine surface group covalently attached to the dendron did not show the carrier transport property. 7 This result indicates that the phenylene-vinylene molecules with different dendrimer are comparably close to each other. We have estimated the structure of the G3D3-PV(TPA) dendrimer was comparably planar shape rather than globular shape. 7

The photocarrier transport property of the three-generation dendrimer, which is composed of phenylene-vinylene as the dendron group and triphenylamine as the surface group G3D3-PV(TPA), was studied by the time of flight (TOF) method using a sandwich-type cell of indium-tin-oxide (ITO)/G3D3-PV(TPA)/Mg-Al. The photocurrent decay shows that hole transport occurs stronger than electron transport, and dispersive transport is observed in the dendrimer film. The mobility at 25 C exhibits negative electric field dependence, and the intrinsic mobility at zero electric field is 7:1 Â 10 À5 cm 2 /(VÁs). This is faster than that of linear poly(p-phenylene-vinylene). Besides this, the result is one order smaller than that of poly(3-hexylthiophene), but faster than those of poly(3-dodecylthiophene) and poly(3-octadecylthiophene). The result indicates that one of the important parameters for the carrier transport is the average distance between -conjugated molecules. The fact that the carrier hopping of the G3D3-PV(TPA) dendrimer occurs effectively implies the structure would be a disk shape since the phenylene-vinylene dendron sites of the different dendrimer molecule are estimated to be close to each other. Recently, -conjugated polymer materials have attracted much interest as potential candidates for use in electro-optical devices, since they exhibit unique features such as flexibility, solubility, and easy film preparation with uniform thickness in large area.

π-Conjugated two generation dendrimer composed of p-phenylenevinylene dendron and triphenylamine surface group was synthesized via a convergent route. The dendrimer shows high solubility in organic solvents and fluorescence emission resulting from the p-phenylenevinylene site.

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