Photosynthetic Antenna–Reaction Center Mimicry by Using Boron Dipyrromethene Sensitizers

Abstract

Various molecular and supramolecular systems have been synthesized and characterized recently to mimic the functions of photosynthesis, in which solar energy conversion is achieved. Artificial photosynthesis consists of light-harvesting and charge-separation processes together with catalytic units of water oxidation and reduction. Among the organic molecules, derivatives of BF2-chelated dipyrromethene (BODIPY), "porphyrin's little sister", have been widely used in constructing these artificial photosynthetic models due to their unique properties. In these photosynthetic models, BODIPYs act as not only excellent antenna molecules, but also as electron-donor and -acceptor molecules in both the covalently linked molecular and supramolecular systems formed by axial coordination, hydrogen bonding, or crown ether complexation. The relationships between the structures and photochemical reactivities of these novel molecular and supramolecular systems are discussed in relation to the efficiency of charge separation and charge recombination. Femto- and nanosecond transient absorption and photoelectrochemical techniques have been employed in these studies to give clear evidence for the occurrence of energy- and electron-transfer reactions and to determine their rates and efficiencies.

Diblock Copolymer Micelles and Supported Films with Noncovalently Incorporated Chromophores: A Modular Platform for Efficient Energy Transfer

“…In the A BODIPY chromophore was chosen as the excitation 'donor' for its favorable stability, hydrophobic character, low tendency to self-aggregate, high extinction coefficient, high fluorescence quantum yield and relatively sharp emission band. 28 We used an analog of BODIPY FL attached through a C 5 -fatty acyl chain to a phosphocholine lipid to direct its assembly, termed "BODIPY-HPC" ( Figure 1B). For the acceptor, a new bacteriochlorin was synthesized, termed "BC-1" (originally, BC-MePy15) 29 ( Figure 1C).…”

“…to fullerenes). 28 While natural LH systems typically rely upon intricate organization of chromophores to direct energy and electron transfers, 33 our system is designed to be much simpler with a self-assembly process that does not require proteins or complex organic synthesis, but instead relies upon incorporation of cofactors into assemblies of amphiphilic polymers.…”

Efficient Charge Separation in Li+@C60 Supramolecular Complexes with Electron Donors

“…The lifetimes of the CS states were in the range of 100-600 ms, which were longer than those of other supramolecular CS systems. [29][30][31][32][33] Such long CS lifetimes resulted from the spin-forbidden charge-recombination process of triplet CS states together with the small electronic coupling terms owing to the separated LUMO and HOMO.…”

“…Supramolecular systems of fullerenes have also attracted attention because they can be easily prepared without complicated and time-consuming synthesis. [29][30][31][32][33][34][35] However, supramolecules of fullerenes with strong binding have rarely been formed in polar solvents, which stabilize the CS state through strong solvation, but destabilize ground-state interactions. When nonpolar solvents are employed to form supramolecules of fullerenes with strong binding, the CS states are destabilized to afford higher CS energy than the triplet excited states of fullerenes.…”

“…Among various electron acceptors, C 60 and its derivatives have most frequently been used to connect with electron donors to achieve efficient photoinduced charge separation and slow recombination because of the high electron affinity and small reorganization energies of electron transfer. [29][30][31][32][33][34][35][36][37][38][39][40] The electron affinity of fullerenes is enhanced by encapsulation of metal atoms in higher fullerenes. [40][41][42][43][44] A pioneering study in endohedral metallofullerenes involved the preparation of La@C 82 , [41] in which three electrons were transferred from the endohedral lanthanum to the C 82 cage with an electronic structure defined as La 3 + @C 82 C 3À .…”