Fig. 3. Photoresponse of a crystalline capsule upon NIR light. (a) Photosalient phenomenon of a crystalline capsule of 1o by multiphoton absorption using femtosecond NIR laser (802 nm) and absorption spectrum of 1o in crystalline state. Absorption wavelength of 1o (<420 nm) is shown in purple and the biological window (650–1350 nm) is shown in pink in the spectrum. Crystal of 1o was excited by multiphoton absorption with femtosecond NIR (802 nm) laser. Two photons of 802 nm correspond to the one photon of 401 nm, which is the tail of the absorbance of the capsule. (b) A crystalline capsule of 1o used in this experiment (left). Upon irradiation of the femtosecond NIR laser (802 nm), the crystalline capsule of 1o was coloured blue (centre part of dark domain is the cavity including hexane solution of 1o). The initial crack was observed at 50 s, and the left side jumped out immediately. The second cracks were observed at 98 s. Then, the missing part of the crystal showed a photosalient phenomenon (99 s). See also ESI Movie S8.†.