Material Clocking by Silica Nanoparticle Precipitation in Solution Phase that is Tunable by Organic Molecules

Material clocking is an important biological phenomenon through which the structure of a material changes sharply with time after activation. A suspension of silica (P)-nanoparticles in the presence of organic molecules in solution exhibits such a material clocking phenomenon during delayed precipitation with high accuracy and precision. A mixture of ethynylhelicene (P)-pentamer and silica (P)-nanoparticles with an average diameter of 70 nm grafted with (P)-helicene in trifluoromethylbenzene is sonicated for activation and dispersion. The (P)-nanoparticles start to precipitate after 3 h of settling at 25 °C and precipitate completely after 4 h. UV/Vis, CD, and DLS analyses of the process show no change during the initial 3 h, but then an abrupt stair-shaped kinetic change occurs with concomitant precipitation and removal of the (P)-pentamer from the solution phase. The delay in the precipitation can be tuned by the structure of molecules added to the (P)-nanoparticle suspension.