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제105회 대한화학회 학술발표회, 총회 및 기기전시회 안내 Excitation Energy Migration Processes in Self-assembled Porphyrin Boxes Constructed by Conjugated Porphyrin Dimers

2010년 2월 18일 10시 50분 48초
34P188포 이곳을 클릭하시면 발표코드에 대한 설명을 보실 수 있습니다.
목 <발표Ⅰ>
저자 및
김표상, Akihiko Tsuda1, 김동호
연세대학교 화학과, Korea
1Kobe University, Japan
Recently, a variety of molecular assemblies as bio-mimic models of natural photosynthetic systems have been synthesized.1,2 Especially, conjugated porphyrin oligomers are highly attractive as building block elements for artificial light harvesting complex, because the linkers have extended conjugation between porphyrin units resulting in low-energy and strong electronic transition of Q bands, which provide enhanced solar spectral absorption and efficient excitation energy hopping (EEH) processes. In this work, we have investigated the EEH processes occuring in the self-assembled zinc(II) porphyrin boxes such as B1, B2, and B4 which are composed of mono-, di-, tetra-alkynylene-bridged porphyrin dimers, respectively. Particularly, alkynylene-linkers allow rotational conformational heterogeneity, which leads to two kinds of self-assembled porphyrin boxes constructed by planar and orthogonal conformers. It was found that the EEH processes occur in the S1 states with the EEH times of 2 ps in all boxes constructed by planar conformers and 12 ps and 8 ps in B2 and B4 constructed by orthogonal conformers, respectively, based on the exciton-exciton annihilation analyses monitored by power-dependent femtosecond transient absorption. According to the calculated Föster energy transfer rate and the observed magnitude and direction of transition dipole moments, increased alkynylene-bridge length leads to the formation of exciton partially localized on porphryin monomer, which result in similar EEH times of all boxes constructed by planar conformers. The dihedral angle of 90 degree provides relatively weak conjugation between porphyrin units, which induces exciton localized state that causes slower EEH times of boxes constructed by orthogonal conformers than that of boxes by planar ones. In conclusion, we suggest that self-assembled zinc(II) porphyrin boxes such as B1, B2, and B4 can be good candidates to realize and control the energy hopping efficiency by tuning alkynylene-bridge length and dihedral angle between porphyrin moieties for artificial light harvesting complexes .