Porphyrin Boxes Constructed by Homochiral Self-Sorting Assembly:  Optical Separation, Exciton Coupling, and Efficient Excitation Energy Migration

• Published in: Journal of the American Chemical Society Vol. 126; no. 49; pp. 16187 - 16198
• Main Authors: Hwang, In-Wook, Kamada, Taisuke, Ahn, Tae Kyu, Ko, Dah Mee, Nakamura, Takeshi, Tsuda, Akihiko, Osuka, Atsuhiro, Kim, Dongho
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 15.12.2004; Amer Chemical Soc
• Subjects: Applied sciences; Biomimetic Materials - chemistry; Chemistry; Chemistry, Multidisciplinary; Circular Dichroism; Exact sciences and technology; Fluorescence Polarization; Inorganic and organomineral polymers; Light-Harvesting Protein Complexes - chemistry; Metalloporphyrins - chemical synthesis; Metalloporphyrins - chemistry; Models, Molecular; Physical Sciences; Physicochemistry of polymers; Properties and characterization; Pyridines - chemical synthesis; Pyridines - chemistry; Science & Technology; Spectrometry, Fluorescence; Stereoisomerism; Zinc - chemistry; FLUORESCENCE; SUPRAMOLECULAR ASSEMBLIES; PHOTOINDUCED ELECTRON-TRANSFER; DIHEDRAL-ANGLE; SPECTROSCOPIC PROPERTIES; BUILDING-BLOCKS; DYNAMICS; MULTIPORPHYRIN ARRAYS; COORDINATION; PHOTOPHYSICAL PROPERTIES; Oligomerization; Molecular structure; Organometallic polymer; Organic ligand; Transition metal Complexes; Radiative lifetimes; Fluorescence spectrometry; Optical anisotropy; Luminescence decay; Optical properties; Metalloporphyrin; Zinc Complexes; Exciton-exciton interactions
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja046241e

meso-Pyridine-appended zinc(II) porphyrins M n and their meso − meso-linked dimers D n assemble spontaneously, in noncoordinating solvents such as CHCl3, into tetrameric porphyrin squares S n and porphyrin boxes B n , respectively. Interestingly, formation of B n from D n proceeds via homochiral self-sorting assembly, which has been verified by optical separations of B1 and B2. Optically pure enantiomers of B1 and B2 display strong Cotton effects in the CD spectra, which reflect the length of the pyridyl arm, thus providing evidence for the exciton coupling between the noncovalent neighboring porphyrin rings. Excitation energy migration processes within B n have been investigated by steady-state and time-resolved spectroscopic methods in conjunction with polarization anisotropy measurements. Both the pump-power dependence on the femtosecond transient absorption and the transient absorption anisotropy decay profiles are directly associated with the excitation energy migration process within the B n boxes, where the exciton−exciton annihilation time and the polarization anisotropy rise time are well described in terms of the Förster-type incoherent energy hopping model by assuming a number of hopping sites of N = 4 and an exciton coherence length of L = 2. Consequently, the excitation energy hopping rates between the zinc(II) diporphyrin units have been estimated for B1 (48 ps)-1, B2 (98 ± 3 ps)-1, and B3 (361 ± 6 ps)-1. Overall, the self-assembled porphyrin boxes B n serve as a well-defined three-dimensional model for the light-harvesting complex.