Excitation Energy Transport Processes of Porphyrin Monomer, Dimer, Cyclic Trimer, and Hexamer Probed by Ultrafast Fluorescence Anisotropy Decay

Abstract

Femtosecond fluorescence anisotropy measurements for a variety of cyclic porphyrin arrays such as Zn(II)porphyrin m-trimer and hexamer are reported along with o-dimer and monomer as reference molecules. In the porphyrin arrays, a pair of porphyrin moieties are joined together via triphenyl linkage to ensure cyclic and rigid structures. Anisotropy decay times of the porphyrin arrays can be well described by the Förster incoherent excitation hopping process between the porphyrin units. Exciton coupling strengths of 74 and 264 cm(-1) for the m-trimer and hexamer estimated from the observed excitation energy hopping rates are close to those of B800 and B850, respectively, in the LH2 bacterial light-harvesting antenna. Thus, these cyclic porphyrin array systems have proven to be useful in understanding energy migration processes in a relatively weak interaction regime in light of the similarity in overall structures and constituent chromophores to natural light-harvesting arrays.

Porphyrin‐Appended Europium(III) Bis(phthalocyaninato) Complexes: Synthesis, Characterization, and Photophysical Properties

“…As revealed by a semiempirical (AM1) study, [26] the centerto-center distance between two porphyrin moieties connected at neighboring positions of a benzene ring through oxygen atoms is only approximately 1.1 nm (see Figure S4 in the Supporting Information), which is near enough for these two neighboring porphyrin chromophores to show electronic interactions. [27,28] As a consequence, a rapid and efficient energy transfer occurs between the two [ZnA C H T U N G T R E N N U N G (TriBPP)] chromophores in 9. It is noteworthy that the timescale of the energy-transfer process in the porphyrin dimer was found to be in the range of 10-100 ps, [29] which is much slower than that of the electron-transfer process from the porphyrin chromophore(s) to [Eu(Pc) 2 ] in the present systems.…”

Excitation Energy Migration in Multiporphyrin Arrays

“…To mimic two-dimensional EET process of natural LH1 and LH2, 6,13 we have constructed the directly-linked cyclic porphyrin arrays CZn of different wheel sizes (Chart 1).…”

“…6 To mimic the wheel-like architecture, two-dimensional cyclic porphyrin arrays (CZn) are constructed by direct and bidirectional inter-porphyrin connections at two meso positions of porphyrin monomer (Chart 1). Because the cyclic porphyrin arrays have well-defined architectures like LH1 and LH2, they can afford comprehensive EET mechanism, especially, the exciton coupling effect on the EET rate.…”

Ultrafast Energy Transfer in the Soret Band of Linear Porphyrin Arrays

“…Various types of porphyrin arrays have been fabricated and the energy transfers within the arrays have been studied to elucidate the factors that control the energy transfer in molecular arrays [1,2]. Among these, meso-meso directly linked porphyrin oligomers may be considered as the most attractive system for the study of energy transfer dynamics due to their rigid, planar, and orthogonal geometry between the porphyrin units [3], which makes it facile to interpret due to the wellarranged directionality.…”