Highly efficient green light-excited AIE photosensitizers derived from BF2-curcuminoid for specific photodynamic eradication of Gram-negative bacteria

Diseases associated with bacterial infection, especially those caused by gram-negative bacteria, have been posing a serious threat to human health. Photodynamic therapy based on aggregation-induced emission (AIE) photosensitizer have recently emerged and provided a promising approach for bacterial discrimination and efficient photodynamic antimicrobial applications. However, they often suffer from the shorter excitation wavelength and lower molar extinction coefficients in the visible region, severely limiting their further applications. Herein, three novel BF2-curcuminoid-based AIE photosensitizers, TBBC, TBC and TBBC-C8, have been rationally designed and successfully developed, in which OCH3- and OC8H17-substituted tetraphenylethene (TPE) groups serve as both electron donor (D) and AIE active moieties, BF2bdk group functions as electron acceptor (A), and styrene (or ethylene) group as π-bridge in this D-π-A-π-D system, respectively. As expected, these resulting BF2-curcuminoids presented solvent-dependent photophysical properties with large molar extinction coefficients in solutions and excellent AIE properties. Notably, TBBC showed an effective singlet oxygen generation efficiency thanks to the smaller singlet-triplet energy gap (ΔEST), and remarkable photostability under green light exposure at 530 nm (8.9 mW/cm2). More importantly, TBBC was demonstrated effectiveness in selective staining and photodynamic killing of Escherichia coli (E. coli) in vitro probably due to its optimal molecular size compared with TBC and TBBC-C8. Therefore, TBBC will have great potential as a novel AIE photosensitizer to apply in the discrimination and selective sterilization between Gram-positive and Gram-negative bacteria.