title: A porphyrin-based molecular tweezer: guest-induced switching of forward and backward photoinduced energy transfer.
abstract: A bisindole-bridged-porphyrin tweezer (1), a pair of zinc porphyrins (PZn's) connected to bisindole bridge (BB) via the Cu(I)-mediated alkyne-azide click chemistry, exhibited unique switching in forward and backward photoinduced energy transfer by specific guest bindings. The addition of Cu(2+) caused a change in electronic absorption and fluorescence quenching of 1. MALDI-TOF-MS and FT-IR analyses indicated the formation of stable coordination complex between 1 and Cu(2+) (1-Cu(II)). Without Cu(2+) coordination, the excitation energy flows from BB to PZn's with significantly high energy transfer efficiency. In contrast, the direction of energy flow in 1 was completely reversed by the coordination of Cu(2+). The difference in fluorescence quantum yield between 1 and 1-Cu(II) indicates that more than 95% of excitation energy of PZn flows into Cu(II)-coordinated BB. The energy transfer efficiency was further controlled by bidentate ligand coordination onto 1-Cu(II). When pyrophosphate ion was added to 1-Cu(II), the recovery of fluorescence emission from PZn was observed. The quantum mechanical calculations indicated that the Cu(II)-coordinated BB has square planar geometry, which can be distorted to form octahedral geometry due to the coordination of bidentate ligands.
authors.affiliation: Department of Chemistry, Yonsei University , 50 Yonsei-ro, Seodaemoon-Gu, Seoul 120-749, Korea.
authors.forename: Hongsik
authors.initials: H
authors.lastname: Yoon
authors.forename: Jong Min
authors.initials: JM
authors.lastname: Lim
authors.forename: Hyuk-Chan
authors.initials: HC
authors.lastname: Gee
authors.forename: Chi-Hwa
authors.initials: CH
authors.lastname: Lee
authors.forename: Young-Hwan
authors.initials: YH
authors.lastname: Jeong
authors.forename: Dongho
authors.initials: D
authors.lastname: Kim
authors.forename: Woo-Dong
authors.initials: WD
authors.lastname: Jang