Chlorophyll a and pheophytin a as gas sensors of CO2 and O2 molecules

► Pheophytin as gas sensors. ► The chlorophyll a and pheophytin a as adsorbent of CO2 and O2 molecules. ► Spin polarization of the O2 molecule higher in the interaction with pheophytin a than with chlorophyll a. ► Charge transfers between pheophytin and CO2 and O2 molecules.