Solution-state mechanochromic luminescence of Pt(ii)-complexes displayed within micellar aromatic capsules.

Mechanochromic luminescence (MCL) is an intrinsic phenomenon and thus has been hardly observed in solution so far. Here we report that arylethynyl Pt(ii)-complexes with an NCN-pincer ligand are efficiently encapsulated by micellar aromatic capsules in water, through a simple grinding protocol with bent amphiphiles. When a bent pentamethylbenzene-based amphiphile is employed as an optimized capsule component, the resultant host-guest composite, with an average diameter of ∼4 nm, is obtained in water at room temperature. Notably, the nanocomposite displays strong red emission ( = 33%, = 700 nm) derived from MCL intermolecular Pt(ii)⋯Pt(ii) interactions even under aerobic aqueous conditions, in sharp contrast to the free Pt(ii)-complex with weak green emission ( = 4%, = 500 nm) in CHCl. Moreover, enhancement of the solution-state MCL (up to = 48%) can be achieved by coencapsulation of the Pt(ii)-complexes with carbazole derivatives by the capsule in water. This study provides the first example of "solution-state" mechanochromic luminescence, capable of facilely tuning its intensity and wavelength, among the intensive studies of various solid-state MCL reported previously.