A series of 1-methylpyridinium-substituted brominated distyryl-BODIPY dyes, PyB X I ( X = H, M, or Br), was synthesized to achieve cooperative singlet oxygen ( ¹ O ₂ ) production through qualitatively different dual intersystem crossing (ISC) pathways: spin–orbit charge-transfer ISC (SOCT-ISC) and heavy-atom-induced ISC. Upon photoexcitation of the PyB X I dyes, charge-transfer states were preferentially formed through photoinduced electron transfer from the distyryl-BODIPY core to the 1-methylpyridinium moiety, however, followed by nonradiative charge recombination rather than the desired SOCT-ISC. This resulted in negligible fluorescence and ¹ O ₂ quantum yields in the non-brominated dye PyBHI. The introduction of bromine atoms improved ¹ O ₂ quantum yield from 0.0034 for the mono-brominated dye PyBMI to 0.0061 for the di-brominated dye PyBBrI, attributable to the heavy atom effect. Nonetheless, the ¹ O ₂ production efficiency of these dyes remained limited, as photoinduced electron transfer was considered to occur nearly two orders of magnitude faster than singlet-to-triplet ISC. In vitro assays using MCF-7 and HeLa cells demonstrated that PyBBrI induced significant cell death, with IC ₅₀ values of ca. 95 and 220 nM, respectively, confirming its potential for use in cancer therapy.

Sb³⁺-ion doping enhances CsPbBr₃ PQD PL properties by suppressing the formation of trap-inducing structural defects and increasing the exciton binding energy and the tolerance factor.