Single chlorophyll-a molecules, a vital resource for the sustenance of lifeon Earth, have been investigated by using scanning-tunneling-microscopemanipulation and spectroscopy on a gold substrate at 4.6 K. The chlorophyll-abinds on Au(111) via its porphyrin unit while the phytyl-chain is elevated fromthe surface by a support of four CH3 groups. By injecting tunneling electronsfrom the STM-tip, we are able to bend the phytyl-chain, which enable switchingof four molecular conformations in a controlled manner. Statistical analysesand structural calculations reveal that all reversible switching mechanisms areinitiated by a single tunnelling-electron energy-transfer process, whichinduces bond rotation within the phytyl-chain.
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