Carbazolyl (iso)phthalonitrile (Cz(I)PN) derivatives are a class of organic dyes with carbazoles as electron donors and a dicyanobenzene as an electron acceptor (Figure ). The small energy gap between the singlet and triplet excited states of these compounds enhances reversible intersystem crossing (RISC), making them suitable for use in organic light-emitting diodes (OLEDs) with thermally activated delayed fluorescence (TADF). Excellent quantum yield (up to 94.6%), a long-excited state lifetime (up to 5.1 s) and a wide redox potential window make them also good photocatalysts in different light-driven transformations. Additionally, the fine-tuning of the photocatalysts can be easily realized by adding electron-withdrawing and electron-donating groups on the carbazole motifs. Since the seminal discovery by Zhang in 2016, over 20 structural variants of CzIPN have been investigated for their photocatalytic properties. These derivatives have shown potential not only as substitutes for traditional iridium (Ir) and ruthenium (Ru) catalysts, but also have enabled novel transformations for photo-mediated small molecule functionalization. Despite the extensive use of Cz(I)PN derivatives in single-electron transfer (SET) and energy transfer (EnT) catalysis for small molecule functionalization, their applications in biological contexts have been limited. The incorporation of peptide sequences interacting with biological targets would enable the use of Cz(I)PN for proximity-driven reactions, with the added advantage of increasing their water solubility (Figure ). Surprisingly, such a strategy has not been reported yet.