The broader redox-potential window, long excited state lifetimes, higher excited state energy, and enhanced solubility of CzBN and CzIPN derivatives in aqueous media indicated a high potential for the photo-functionalization of biomolecules. First, we attempted the photomediated C-terminal decarboxylative alkynylation of peptides originally catalyzed by 4CzIPN (Figure ). Compared to 4CzIPN, conjugates 3za and 6aa produced the alkynylated product 8a with a slight decrease of yield for the protected dipeptide Cbz-GP-OH. We further tested the catalytic reactivity of the conjugates on a longer tetramer peptide, AcHFGP-OH. The alkynylation reaction (8b) proceeded with both conjugates 3za and 6aa, achieving HPLC yields of 15% and 51%, respectively. The latter is comparable to the yield obtained with non-modified 4CzIPN (52%). Encouraged by these results, we conducted this reaction in aqueous media using water-soluble conjugates 3ya and 6ca. Unfortunately, no decarboxylation occurred with either catalyst using a simple dipeptide as the model substrate, likely due to differences in redox potential for the dyes in the two reaction solvents.