Characterisation of the reaction of free-base porphyrin to nitrogen dioxide

The response of 5,10,15,20-tetrakis(3,4-bis[ethylhexyloxy]phenyl)-21H,23H-porphine (EHO) to NO2 has been measured, both in solution and in Langmuir–Blodgett (LB) films. A change in the absorption spectrum has been observed, characterised by the reduction of the Soret and Q bands accompanied by the rise of two new bands at 464 and 697 nm in solution. The response of free-base porphin to NO2 has been modelled using the Accelrys Materials Studio software. A good qualitative agreement can be seen between the predicted change in absorption spectrum for free-base porphin and the response observed for EHO. LB films of EHO/calixarene mixes showed a response to NO2 similar in form to the response of EHO in solution.