Chloride anion controlled molecular "switching". Binding of 2,5,7-trinitro-9-dicyanomethylenefluorene-C₆₀ by tetrathiavulvalene calyx[4]pyrrole and photophysical generation of two different charge-separated states

Nielsen, K.A., Sarova, G.H., Martin-Gomis, L., Fernandez-Lazaro, F., Stein, P.C., Sanguinet, L., Levillain, E., Sessler, J.L., Guldi, D.M., Sastre-Santos, A. and Jeppesen, J.O.

J. Am. Chem. Soc. 130(2), 460-462 (2008)

NDRL 4759

The binding of the snake-like trinitrodicyanomethylenefluorene-C₆₀ derivative (TNDCF-C₆₀) to the dynamic receptor, tetrathiafulvalene calix[4]pyrrole (TTF-calix[4]pyrrole), may be controlled via the use of a chloride anion as an external trigger. Whereas, in the absence of a chloride anion, the TNDCF "tail" of the trinitrodicyanomethylenefluorene-C₆₀ substrate binds to the TTF-calix[4]pyrrole in a 2:1 (substrate/receptor) stoichiometry in CH₂Cl₂ solution, addition of a chloride anion (yellow) leads the TNDCF tail to be displaced in favor of a bound C₆₀ "head", a process that leads to the formation of a complex with overall 1:2:2 substrate/receptor/chloride anion stoichiometry. These chemical switching events are reflected in easy-to-visualize color changes, as well as in the production of two different kinds of charge-separated states following selective femtosecond photoexcitation.