Macrocycle ring and peripheral group sizes-dependent vapor sensing property of copper phthalocyanine thin films

Abstract

Spin-coated thin films of copper phthalocyanine (CuPc) were fabricated using different rotation speeds from 250 rpm to 1250 rpm. The structural characterization of these films was analyzed using UV-vis spectroscopy and atomic force microscopy (AFM). Gas sensing properties of these spun thin films were investigated against different volatile organic compounds such as chloroform, dichloromethane and toluene using surface plasmon resonance (SPR) technique. CuPc thin films were found to be highly sensitive to chloroform and dichloromethane vapor with fast response and recovery times. These measurements clearly indicated that the CuPc molecule is a promising material for the development of the room temperature vapor sensing applications with sensitivities between 4 x 10(-6) and 15 x 10(-6) percent response ppm(-1). Three different functional groups of CuPc structures coded as CuPc I, II and III were investigated which differ from each other in their chemical structures in terms of their microcycle ring groups and peripheral groups, all attached to the same free base porphyrin skeleton. The number of microcycle ring groups and peripheral groups were found to be efficient on the gas sensing properties. The calculated refractive index and extinction coefficients using SPR curves were 1.54, 0.84 for CuPc I thin film, 1.64, 0.13 for CuPc II thin film and 1.71, 0.22 for CuPc III thin film, respectively. For different substrate rotation speeds, the thin film thicknesses vary between 2 nm and 6 nm for CuPc I and CuPc III thin films whereas it ranges between 4 nm and 9 nm for CuPc II thin film.