Folding and unfolding of chromophoric foldamers show unusual colorful single molecule spectral dynamics

A series of well-defined linear multichromophoric foldamers with a specific sequence of alternating rigid perylene chromophores and flexible ethylene glycol chains were studied by single molecule fluorescence spectroscopy. Monomer showed minor spectral fluctuations compared to trimer and hexamer, which showed unusual and colorful spectral dynamics attributed to a stochastic photoinduced unfolding/folding phenomenon. The range of spectral shapes observed indicates varying degrees of pi-pi interaction between adjacent chromophores, with vibronically resolved green emission indicating completely unfolded structures and broad red emission indicating highly coupled and extensively folded pi-stacks. The rate of switching between different spectral shapes in the spectral trajectories suggests the existence of multiple pathways between the folded and unfolded states.