미소접촉인쇄와 랭뮈어-블로젯을 이용한 포르피린 패턴 제작

Abstract

Porphyrin and its derivatives are attractive due to advantageous properties that include chemical and thermal stability, rigidity, optical and electronic properties and anisotropy. Owing to these properties, they are finding potential applications in data storage, photodynamic therapy (PDT), photovoltaics, and optical sensing. In particular, porphyrins have been widely used as active materials in gas and pH sensors because of their high sensitivity, broad selectivity, and fast response. Porphyrin-containing sensor systems are generally based on electrochemical, optical, or surface plasmon resonance (SPR) measurements. The optical technique is particularly appealing because porphyrins possess extremely rich UV-vis absorption spectra due to their highly conjugated π-electron system. While there are numerous reports of sensors based on porphyrin films, to the best of our knowledge there are no reports related to patterned porphyrin sensor devices. In this study, we demonstrate a simple and straightforward method to pattern porphyrin molecules using Langmuir-Blodgett (LB) deposition and micro-contact printing (μ-CP). The general procedure consists of the following steps. First, a surface-patterned polydimethylsiloxane (PDMS) mold is replicated from a photoresist-patterned silicon substrate. Secondly, LB films of the porphyrins are deposited on the surface of the patterned PDMS. Lastly, the porphyrin LB films are selectively transferred onto Si-wafer or quartz substrates using the μ-CP technique. The combination of LB deposition and μ-CP can conveniently fabricate micron and submicron-sized patterns of well-ordered and densely-packed porphyrin molecules. Note that the dicyanopyrazine-linked porphyrin (2-DCPP) films cannot be obtained by conventional methods such as spin-coating and thermal evaporation because of crystallization and thermal degradation properties of the 2-DCPP molecules. Thus, this methodology is suitable for fabricating 2-DCPP patterns and we believe this method can expand the limits of molecules which are suitable for sensor devices. AFM images reveal that the sizes and shapes of the 2-DCPP patterns are well-matched with the geometric features of the PDMS stamps used for μ-CP. Fluorescence images show strong, red emission from the 2-DCPP patterns. However, the thicknesses of the 2-DCPP patterns transferred onto a silicon substrate by μ-CP are not the same, even though the same amount of 2-DCPP layers are deposited on the surface of PDMS stamps in the LB process. The thicknesses of the 10 µ m line, 2 µ m dot and 300 nm line patterns of 10-layered 2-DCPP molecules are 33.8, 27.8 and 11.2 nm, respectively. These differences may be due to variations in adhesion forces between the silicon substrate and 2-DCPP on PDMS stamps having different size patterns. Larger patterns have greater contact areas compared to smaller patterns. This phenomenon can cause stronger adhesion forces, resulting in greater pattern thickness. Spectral changes of the Soret and Q bands of UV-vis and photoluminescence spectra of 2-DCPP LB film upon acid vapor exposure have also been investigated. These measurements demonstrate acid vapor sensing capability and chemical sensor application of the chromophoric systems of the dicyanopyrazine-linked porphyrin.