Efficient Excitation Energy Transfer in Long Meso−Meso Linked Zn(II) Porphyrin Arrays Bearing a 5,15-Bisphenylethynylated Zn(II) Porphyrin Acceptor

• Published in: Journal of the American Chemical Society Vol. 125; no. 32; pp. 9668 - 9681
• Main Authors: Aratani, Naoki, Cho, Hyun Sun, Ahn, Tae Kyu, Cho, Sung, Kim, Dongho, Sumi, Hitoshi, Osuka, Atsuhiro
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 13-08-2003
• Subjects: Alkynes - chemistry; Atomic and molecular collision processes and interactions; Atomic and molecular physics; Benzene Derivatives - chemical synthesis; Benzene Derivatives - chemistry; Biomimetic Materials - chemical synthesis; Biomimetic Materials - chemistry; Boronic Acids - chemistry; Cross-Linking Reagents - chemical synthesis; Cross-Linking Reagents - chemistry; Energy Transfer; Exact sciences and technology; Fluorescence and phosphorescence; radiationless transitions, quenching (intersystem crossing, internal conversion); Fluorescence Polarization; Intramolecular energy transfer; intramolecular dynamics; dynamics of van der waals molecules; Metalloporphyrins - chemical synthesis; Metalloporphyrins - chemistry; Molecular properties and interactions with photons; Physics; Radiationless transitions, quenching; Rotational and vibrational energy transfer; Spectrometry, Fluorescence; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Fluorescence spectroscopy; Time of flight mass spectroscopy; Transition elements Complexes; Light harvesting system; Nitrogen heterocycle; Organic ligand; Metalloporphyrin; Radiative lifetimes; Experimental study; Intramolecular energy transfer; Zinc Complexes; Luminescence decay
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja030002u

Electronically coupled porphyrin arrays are suitable for artificial light harvesting antenna in light of a large absorption cross-section and fast excitation energy transfer (EET). Along this line, an artificial energy transfer model system has been synthesized, comprising of an energy donating meso − meso linked Zn(II) porphyrin array and an energy accepting 5,15-bisphenylethynylated Zn(II) porphyrin linked via a 1,4-phenylene spacer. This includes an increasing number of porphyrins in the meso − meso linked Zn(II) porphyrin array, 1, 2, 3, 6, 12, and 24 (Z1A, Z2A, Z3A, Z6A, Z12A, and Z24A). The intramolecular singlet−singlet EET processes have been examined by means of the steady-state and time-resolved spectroscopic techniques. The steady-state fluorescence comes only from the acceptor moiety in Z1A − Z12A, indicating nearly the quantitative EET. In Z24A that has a molecular length of ca. 217 Å, the fluorescence comes largely from the acceptor moiety but partly from the long donor array, indicating that the intramolecular EET is not quantitative. The transient absorption spectroscopy has provided the EET rates in real time scale:  (2.5 ps)-1 for Z1A, (3.3 ps)-1 for Z2A, (5.5 ps)-1 for Z3A, (21 ps)-1 for Z6A, (63 ps)-1 for Z12A, and (108 ps)-1 for Z24A. These results have been well explained by a revised Förster equation (Sumi formula), which takes into account an exciton extending coherently over several porphyrin pigments in the donor array, whose length is not much shorter than the average donor−acceptor distance. Advantages of such strongly coupled porphyrin arrays in light harvesting and transmission are emphasized in terms of fast EET and a large absorption cross-section for incident light.