Hemes, chlorophylls and pheophytins are pigments that play an essential role in biology, whether for photosynthesis, oxygen transport or numerous enzymatic catalyses. One of the many open questions is how small molecules interact with the metal cations at the heart of pigments (e.g. Fe(II/III), Mg(II), Co(III), …). We collaborate with Dr. Niloufar Shafizadeh’s team (Institut des Sciences Moléculaires d’Orsay, CNRS, U. Paris Saclay), which carries out gas-phase molecular photophysics experiments. We perform quantum chemical calculations to better understand the coordination, electronic and vibrational properties of these molecules. Some examples of recent studies are given below.