Mechanically steered photon upconversion and circularly polarized luminescence in stretchable photonic crystal films

Photon-upconverted circularly polarized luminescence (UC-CPL) based on triplet-triplet annihilation (TTA) holds considerable promise for innovative applications. However, existing strategies encounter difficulties in concurrently achieving tunable TTA photon upconversion (TTA-UC) performance and a high luminescence dissymmetry factor (g_lum) in the solid state. In this study, we design and fabricate flexible and stable upconverted stretchable photonic crystal (SPC) films. These films demonstrate dynamically tunable TTA-UC intensity and UC-CPL in response to mechanical stretching. Notably, while the TTA-UC intensity initially diminishes upon stretching the upconverted SPC film, it subsequently exhibits significant enhancement when the photonic bandgap edge aligns with the TTA-UC emission wavelength. Furthermore, stretching the upconverted SPC film can invert the circular polarization direction of the UC-CPL, with the g_lum value varying from +0.50 to -0.60. Consequently, these upconverted SPC films, characterized by their tunable structural color and adjustable UC-CPL, achieve visual flexible dynamic information display and encryption. This research offers promising perspectives for the development of advanced chiral UC-CPL materials and their potential applications in fields such as information encryption and flexible 3D displays.