We study the origin of the large Seebeck coefficient despite the metallic conductivity in the Ladoped SrTiO3 and Ba-doped KTaO3. We calculate the band structure of SrTiO3 and KTaO3, from which the Seebeck coefficient is obtained using the Boltzmann's equation. We conclude that the multiplicity of the t2g bands in these materials is one major origin of the good thermoelectric property in that when compared at a fixed total number of doped electrons, the Seebeck coefficient and thus the power factor are larger in multiple band systems than in single band ones because the number of doped electron bands per band is smaller in the former. We also find that the second nearest neighbor hopping integral, which generally has negative values in these materials and works destructively against the Seebeck effect, is nearly similar between KTaO3 and SrTiO3 despite the larger band width in the former. This can be another factor favorable for thermopower in the Ba-doped KTaO3.

INTRODUCTION Some [2.2]paracyclophane compounds 1,2 exhibit planar chirality, a unique feature derived from suppressed rotary motion in the two fixed phenylene units. 2-4 Various [2.2]paracyclophanes have been optically resolved, 3-7 and optically active [2.2] paracyclophane compounds have been used mainly as chiral auxiliaries in the fields of organic and organometallic chemistry. Recently, we studied planar chiral [2.2] paracyclophanes and developed a novel approach to obtain enantiopure 4,12-disubstituted 6 and 4,7,12,15-tetrasubstituted [2.2] paracyclophanes. 8 These molecules were employed as chiral building blocks to construct optically active through-space-conjugated systems in an effort to apply planar chirality in the fields of polymer and materials chemistry. Here, we report the synthesis of optically active through-space-conjugated copolymers consisting of enantiopure 4,12-disubstituted [2.2]paracyclophane and quaterthiophene to expand the substrate scope. In a single polymer chain, 2,2′′′-dixylyl-2,2′:5′,2′′:5′ ′,2′′′-quaterthiophenes are stacked by the [2.2]paracyclophane skeleton. 9,10 In addition to the previously reported optical resolutions by the diastereomer method, 6 chromatographic optical resolutions of key compounds with chiral columns were successfully carried out. The obtained polymers exhibited beneficial chiroptical properties such as circularly polarized luminescence (CPL) with a relatively large CPL dissymmetry factor (g lum ). We disclose herein that the optically active through-space-conjugated polyarylenes, instead of poly(p-aryleneethynylene)s, emit clear CPL due to the planar chiral [2.2] paracyclophane.

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A [2.2]paracyclophane-based through-space conjugated oligomer comprising three π-electron systems was designed and synthesized. The arrangement of three π-conjugated systems in an appropriate order according to the energy band gap resulted in efficient unidirectional photoexcited energy transfer by the Förster mechanism. The energy transfer efficiency and rate constants were estimated to be >0.999 and >10(12) s(-1), respectively. The key point for the efficient energy transfer is the orientation of the transition dipole moments. The time-dependent density functional theory (TD-DFT) studies revealed the transition dipole moments of each stacked π-electron system; each dipole moment was located on the long axis of each stacked π-electron system. This alignment of the dipole moments is favorable for fluorescence resonance energy transfer (FRET).

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