Light-harvesting supramolecular porphyrin macrocycle accommodating a fullerene-tripodal ligand.
Trisporphyrinatozinc(II) (1-Zn) with imidazolyl groups at both ends of the porphyrin self-assembles exclusively into a light-harvesting cyclic trimer (N-(1-Zn)(3)) through complementary coordination of imidazolyl to zinc(II). Because only the two terminal porphyrins in 1-Zn are employed in ring formation, macrocycle N-(1-Zn)(3) leaves three uncoordinated porphyrinatozinc(II) groups as a scaffold that can accommodate ligands into the central pore. A pyridyl tripodal ligand with an appended fullerene connected through an amide linkage (C(60)-Tripod) was synthesized by coupling tripodal ligand 3 with pyrrolidine-modified fullerene, and this ligand was incorporated into N-(1-Zn)(3). The binding constant for C(60)-Tripod in benzonitrile reached the order of 10(8) M(-1). This value is ten times larger than those of pyridyl tetrapodal ligand 2 and tripodal ligand 3. This behavior suggests that the fullerene moiety contributes to enhance the binding of C(60)-Tripod in N-(1-Zn)(3). The fluorescence of N-(1-Zn)(3) was almost completely quenched (approximately 97 %) by complexation with C(60)-Tripod, without any indication of the formation of charge-separated species or a triplet excited state of either porphyrin or fullerene in the transient absorption spectra. These observations are explained by the idea that the fullerene moiety of C(60)-Tripod is in direct contact with the porphyrin planes of N-(1-Zn)(3) through fullerene-porphyrin pi-pi interactions. Thus, C(60)-Tripod is accommodated in N-(1-Zn)(3) with a pi-pi interaction and two pyridyl coordinations. The cooperative interaction achieves a sufficiently high affinity for quantitative and specific introduction of one equivalent of tripodal guest into the antenna ring, even under dilute conditions ( approximately 10(-7) M) in polar solvents such as benzonitrile. Additionally, complete fluorescence quenching of N-(1-Zn)(3) when accommodating C(60)-Tripod demonstrates that all of the excitation energy collected by the nine porphyrins migrates rapidly over the macrocycle and then converges efficiently on the fullerene moiety by electron transfer.
Kuramochi
Yusuke
Y
Graduate School of Materials Science, Nara Institute of Science and Technology, Takayama 8916-5, Ikoma, Nara 630-0101, Japan.
Satake
Akiharu
A
Itou
Mitsunari
M
Ogawa
Kazuya
K
Araki
Yasuyuki
Y
Ito
Osamu
O
Kobuke
Yoshiaki
Y
D037741:Fullerenes / Q000737:chemistry* / Q000528:radiation effects; D008024:Ligands; D008027:Light; D047028:Macrocyclic Compounds / Q000138:chemical synthesis / Q000737:chemistry* / Q000528:radiation effects; D046911:Macromolecular Substances / Q000138:chemical synthesis / Q000737:chemistry / Q000528:radiation effects; D009682:Magnetic Resonance Spectroscopy / Q000379:methods / Q000592:standards; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry* / Q000528:radiation effects; D011166:Porphyrins / Q000737:chemistry* / Q000528:radiation effects; D012015:Reference Standards; D013237:Stereoisomerism; D013997:Time Factors; D015032:Zinc / Q000737:chemistry / Q000528:radiation effects
D037741:Fullerenes; D008024:Ligands; D047028:Macrocyclic Compounds; D046911:Macromolecular Substances; D009942:Organometallic Compounds; D011166:Porphyrins; D015032:Zinc