Fluorescence Dynamics of Chlorophyll Trefoils in the Solid State Studied by Single-Molecule Fluorescence Spectroscopy

We have comparatively investigated the single-molecule-photophysical properties of two chlorophyll trefoils that feature distinctive electronic couplings induced by differences in linkage: one is an ethynyl-linked chlorophyll trefoil (1) in which relatively short and rigid linkage between the chromophores promotes effective electronic coupling, and the other is a phenyl ethynyl-linked chlorophyll trefoil (2) in which the phenyl addition induces an orthogonal geometry impeding pi-conjugation and provides a longer interchlorophyll distance reducing through space interaction. By recording single molecule fluorescence intensity trajectories and their corresponding lifetimes, we observed one-step photobleaching behaviors, less frequent on off behaviors, a narrower fluorescence lifetime distribution, and higher photostability in 1 as compared with 2. These results indicate that the performance of molecular photosynthetic systems in the solid state is strongly associated with electronic couplings and; thus, give insight into the construction of well-functioning artificial photosynthetic systems.