Then, we aimed to determine whether aryl azides 11, with a triplet state energy of 43.9 kcal/mol, could be excited through energy transfer (EnT) using the peptide conjugates (excited energy above 60.0 kcal/mol). We were pleased to observe successful excitation of both aryl azide and perfluorinated aryl azide using either 4CzBN 3za or 3CzIPN conjugates 6aa under 467 nm irradiation from a Kessil lamp (See Supporting Information section 8.3.2 for details). Notably, 3CzIPN conjugates exhibited higher excitation efficiency. Encouraged by these results, we further explored the potential of in-vitro protein labelling enabled by these dye conjugates (Figure ). We conducted the reaction on bovine serum albumin (BSA) using a biotin-conjugated aryl azide probe (11a) with a PEG linker to enhance water solubility. The photolabeling reactivity of the conjugates was assessed via Western blotting of the reaction mixture with HRP-conjugated streptavidin to detect the amount of biotinylated BSA. A notable biotinylation level was observed when the reaction was performed in a PBS buffer after only 15 minutes of irradiation with a 467 nm Kessil lamp (40 W, intensity: 100%) in the presence of 6ca. The level of protein biotinylation correlated with the concentration of 6ca. In contrast, direct excitation of BSA with 467 nm light alone resulted in minimal labelling. Similar outcomes were observed with perfluorinated aryl azide excitation (11b), a compound that facilitates the generation of nitrene species with extended lifetimes, providing protein labelling with different labelling radius. With the success of in-vitro protein labelling via aryl azide excitation, we extended this method to living cell systems with the goal to exploit the potential for proximity-driven labelling offered by the binding peptide. Compared to the previous aryl azide excitation with a Ir and Os catalyst, which required the pre-installation of photocatalyst onto an antibody, and was limited to extracellular protein targets, peptide sequences allow us potentially to target both intraand extracellular targets. To validate the potential of targeting intracellular targets, we used CPP (cell penetrating peptide)-3CzIPN conjugate 6fa as the photosensitizer together with azide 11c, which is small enough to cross the cell membrane (Figure , DIC imaging in Supporting Information Section 8.7.2). We observed significant fluorescent pattern overlap between the nitrene labelling region (revealed through CuAAC between a Cy5 azide reagent and the terminal alkyne on 11c) and the CzIPN conjugate region inside Hela cells (See Supporting Information section 8.7 for experimental details). As an extracellular target of high biological relevance, we chose integrins, which are a class of cell adhesion receptors playing a crucial role in mediating signal transduction between cells and the extracellular matrix (ECM). Notably, the αvβ3 integrin subtype is frequently overexpressed in different cancer cells. Consequently, it has emerged as a promising therapeutic target for the development of cancer treatments. To further underscore the application of peptide sequences on 3CzIPN to realize protein specific labelling, we used the modified integrin αvβ3 binder 6ia to probe the interactome of integrin αvβ3 (Figure , DIC imaging in Supporting Information Section 8.7.3). We selected the A549 cell line, known for its high expression of integrin αvβ3. The cells were first incubated with the integrin αvβ3 binder 6ia for one hour, followed by washing and subsequent incubation with the aryl azide probe 11c. After the photoexcitation of aryl azide probe, the cells were fixed and subjected to immunofluorescence (IF) staining with FITC conjugated integrin αvβ3 antibody to determine the localization of the target protein. The labeling region of the aryl azide was visualized through CuAAC between a Cy5 azide reagent and the terminal alkyne on 11c. We were pleased to observe a strong overlap between the antibody signal and the Cy5 signal, showing that aryl azide excitation had occurred in a close proximity to integrin. After the photoreaction, the localization of the photocatalyst 6ia also showed a good overlap with both the andibody and the Cy5 dye, although the signal on the membrane was weaker. This may be due to a fast photobleaching of the dye on the membrane during irradiation. In both the cases of intracellular and extracellular aryl azide excitation, cells remained in good viability before and after light irradiation, highlighting the potential of using 3CzIPN-peptide conjugates in live systems (Figure ).