Evaluation of structure and gas response in porphyrin Langmuir-Blodgett films by attenuated total reflection measurements

Attenuated total reflection (ATR) properties were measured for porphyrin Langmuir-Blodgett (LB) films, and the structure and response to NO2 gas were investigated. The porphyrin molecule was 5,10,15,20-tetrakis(3,4-bis[2-ethylhexyloxyphenyl])-21H,23H-porphine (EHO). The EHO LB films were deposited onto Ag evaporated glass substrates by a vertical dipping method with an ultrafast deposition rate of 1000 mm/min. The response of optical absorbance to NO2 gas was very fast. The thickness and the complex dielectric constants of the EHO LB films evaluated from the ATR properties measured at 632.8 nm were thought to be related to the island structure of the EHO LB films. The isolated micron-size domains, which are themselves composed of grains of several nm in diameter, were also observed in the EHO LB films by atomic force microscopy. The ATR properties at 488.0 nm were considered to be related to the dispersion properties due to the optical absorption band of the EHO LB films. From the NO2 gas response measurements, the ATR properties at 488.0 nm were found to be more sensitive than those at 632.8 nm. The response to NO2 gas and the recovery properties in the ATR measurements were also examined.