Characterization, second-harmonic generation, and gas-sensitive propertiesof Langmuir-Blodgett films of 1,8-naphthalimide-tri-tert-butylphthalocyanine

Langmuir-Blodgett (LB) films of a new metal-free asymmetrically substituted phthalocyanine (Pc), 1,8-naphthalimide-tri-tert-butylphthalocyanine (NaBuP c), were fabricated and characterized by UV-vis spectrometry, atomic force microscopy, and small-angle X-ray diffraction (SAXRD). The results proved t hat the asymmetrically substituted Pc not only possesses good solubility in common organic solvents but also possesses an ideal LB film forming abilit y. From its surface pressure-area isotherm and SAXRD pattern, the configura tion of the phthalocyanine molecules both at the air-water interface and in the LB films was demonstrated at a tilted angle (72 degrees) to the water surface or solid substrate. The second-harmonic generation (SHG) of a three -layer LB film of NaBuPc was measured. Its SH intensity relative to a U-cut quartz wedge I-2 omega(p-->p) is approximately 1.76. The values of second- order susceptibility (chi ((2))) and the molecular hyperpolarizability (bet a) from the multilayers are 8.32 x 10(-9) and 5.97 x 10(-30) esu, respectiv ely. Gas sensors based on the LB films of NaBuPc demonstrated good gas sens itivity to nitrogen dioxide at room temperature. A linear relationship betw een the logarithm of the concentration of NO2 and the resistance of the sen sor was observed, providing a basis for the application as gas sensors ih t he future.