A dual-frequency photonic crystal nanocolloid with hue- and brightness-tunable structural colors

Self-assembled lamellar nanocolloids of two-dimensional (2D) nanosheets can provide new possibilities for tunable photonic crystalline devices based on their vivid structural color and reconfigurability. However, this remains a challenge because of the veiled dynamic behavior of 2D nanocolloids under electric fields and the lack of feasible manipulation methods. Here, we demonstrate a full-color tunable polyoxyalkyleneamine-tethered α-TiP nanocolloid possessing the ability to tune hue and brightness by harnessing field-induced phase transition phenomena, in which the intrinsic lamellar phase can transition to an optically anti-nematic phase via an isotropic phase at high-frequency fields and vice versa at low-frequency fields. This unique switching behavior is attributed to the formation of a dynamic polydomain structure characterized by stable intradomain lamellar ordering and reconfigurable interdomain ordering. This causes a clear discrepancy between optical observations and X-ray scattering measurements. By exploiting these, a switchable and multistable photonic crystalline device is successfully demonstrated.