Understanding the interactions of porphryin LB films with NO2

The optical properties of a substituted porphyrin compound have been investigated in order to correlate the UV–vis absorption spectrum with both the chemical structure of the porphyrin and the analyte to which Langmuir–Blodgett (LB)/Langmuir–Schaeffer (LS) films of the porphyrin have been exposed. A dramatic change in the characteristic porphyrin spectrum is observed with a fast reduction of the absorption intensity of the Soret band. Computational modeling of these porphyrin interactions using Accelrys MS Modeling 3.1 software has provided some understanding of the nature of the analyte-porphyrin binding. Experimental parameters which relate the transfer of oscillator strength from the Soret band (at ∼426 nm in CHCl3 solution) to two new lower energy transitions (at ∼463 and 698 nm in CHCl3 solution) to the adsorption of analyte species have been investigated. It is shown that the film quality of LB/LS films of 5,10,15,20-tetrakis[3,4-bis(2-ethylhexyloxy)phenyl]-21H,23H-porphine (EHO), and therefore their operation as optical NO2 gas sensors, can be greatly improved using a mixed EHO/calixarene Langmuir layer.