We aimed to design a chemical probe to specifically, covalently label FPR1 on the surface of cells. Photocrosslinkers have a history of successful use in trapping GPCR-peptide ligand interactions and a benzophenone-based fluorescent probe has been shown to bind FPR1, act as an agonist and enable crude mapping of the binding site. However, benzophenone has limited resolution as a photocrosslinker and its bulk and hydrophobicity can enhance non-specific binding. Two recent structures of formyl peptide ligands (fMLF and fMLFII) bound to FPR1 show that the formylated N-terminus reaches deep inside the receptor to a cluster of hydrophobic residues proposed to act as a nexus for activation. We hypothesised that alkyl diazirines, with their small size, rapid irreversible activation and crosslinking, and non-polar properties, would be ideal crosslinking groups for incorporation into FPR1 ligands.