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  • 09월 08일 17시 이후 : 초록수정 불가능, 일정확인 및 검색만 가능

제116회 대한화학회 학술발표회, 총회 및 기기전시회 안내 Designing Bimetallic Complexes for Efficient Light-Driven Redox Catalysis: How to Assign Specific Functions to Each Metal in a Bimetallic Ir(III)-Pt(II) Complex

2015년 9월 3일 13시 24분 18초
IND.P-89 이곳을 클릭하시면 발표코드에 대한 설명을 보실 수 있습니다.
10월 16일 (금요일) 13:00~14:30
저자 및
조양진, 조대원, 강상욱, 손호진*
고려대학교 소재화학과, Korea
The electronic communication between two metal-centers in a bimetallic complex is studied using experimental and computational techniques. Using 2,3-bis(2-pyridyl)pyrazine as a linker, the light-absorbing Ir-chromophore fragment [(2-(4’,6’-difluorophenyl)pyridinato-N,C2)2Ir]+ is coupled to a PtCl2 unit that serves as a model for a redox-active catalyst not absorbing light. The modular design of bimetallic catalysts, in which a chromophore complex and a redox-active metal center can be combined to engineer a photocatalytic system is an attractive general strategy: The chromophore is envisioned to harvest light energy utilizing a metal to ligand charge transfer (MLCT) absorptions, placing activated electrons onto the bridging linker moiety. These electrons must be transferred to the other metal center to be used as reducing equivalents during redox catalysis. Our studies suggest that the bimetallic system does not perform properly as envisioned ? instead of remaining spectroscopically silent, the Pt(II)-center develops enhanced absorption features and the envisioned flow of electrons from the photosensitizer to the redox-center does not take place. Our computational analysis of the electronic structures of each modular fragments and the fully assembled bimetallic complex revealed some simple principles of control: For the Ir-chromophore to remain the main photoactive component in the bimetallic assembly, the Pt-based frontier orbitals must not become one of the highest lying occupied orbitals, as the small energy difference to the ligand-based unoccupied orbitals will give rise to new enhanced absorptions, as was the case in the [Ir]-PtCl2 system. To test this new insight, a new bimetallic complex, [Ir]-Pt(CN)2, was prepared. The much stronger ligand field of the cyanide ligand lowered the Pt-based orbitals, effectively switching off any Pt-based photoactivity and restoring the intended electron flow within the bimetallic assembly. TDDFT calculations are used to quantify the absorptions, but the main qualitative insight is derived from standard MO-diagrams that are intuitively understandable. The workflow showcased here, which integrates computational and experimental techniques, is a general procedural template for rationally designing modular multicomponent catalysts.