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.