Fig. 3. (a) Photographs of the crystals of PER, d-Fru and d-Gal taken at room temperature after stopping UV irradiation at different wavelengths. (b) Photographs of concentrated aqueous solutions for PER (0.1 M), d-Fru (1 M) and d-Gal (1 M) taken at 77 K after stopping UV irradiation at different wavelengths. (c) Decay profiles of the crystals of PER, d-Fru and d-Gal monitored at varying λems at room temperature (rt). (d) Excitation–p-RTP mapping and p-RTP spectra with different excitations (td = 0.1 ms) for PER crystals. (e) Trajectory of tunable p-RTP colors of PER crystals, recorded as the change in the λex from 245 to 325 nm, in the CIE coordinate diagram. (f) Single crystal structure of PER with the intra- and intermolecular O⋯O interactions marked. (g) Fragmental molecular packing of PER in crystals with the O⋯O short contacts marked.
