Luminescence lifetime tuning of non-conjugated organic clusters through external heavy-atom effect for smartphone-based time-resolved imaging

Clusteroluminescence from non-conjugated organic molecules has attracted extensive attention, and it is extraordinarily important to develop effective methods for tuning the clusteroluminescence lifetime with balanced emission intensity in optical multiplexing for time-resolved luminescence imaging. Herein, chitosan, a renewable polymer, was found to exhibit persistent clusteroluminescence after dehydration. In addition, external heavy-atom effect was successfully utilized for enhancing phosphorescence intensity and regulating its phosphorescence lifetime. By adjusting the doping concentration of bromide salts in chitosan, the phosphorescence lifetime could be gradually tailored from 49 to 647 ms. The heavy atoms could promote phosphorescence transition and avoid the reduction of short-lived luminescence component, which facilitated the lifetime-multiplexed information encryption. This strategy for tuning phosphorescence lifetime could be extended to other phosphorescence materials. Moreover, smartphone-based luminescence imaging of shrimp chitin was realized by enhancing its persistent luminescence, which indicated that our method could be used for label-free luminescence imaging of chitin-containing organisms.