Fig. 5.
a Structure of P1. b PL spectra of P1 in different states. c Images of P1 powder in different states without (left) and with (right) the illumination of UV light. Reproduced from [28] with permission from Springer Nature. d Illustration of fluffy poly-l-proline (PPRO) in response to pressure. Reproduced from [50] with permission from the Royal Society of Chemistry