Photoresponsive Colorimetric Change of a t-BOC-Polyaniline/Spiropyran Film Based on Conducting Pattern

Abstract

Among the polymers, polyaniline (PANI) is a unique conjugated polymer in that it can be tailored for specific applications through a non-redox acid/base doping process. 1-3Unfortunately, Its poor solubility in most common organic solvents has limited the industrial application of PANI because of its high aromatic nature, strong inter-chain hydrogen bonding, and high charge delocalization. The patterning of conjugated polymers on various substrates was achieved by using a variety of techniques, such as the deposition by scanning electrochemical microscopy, 4 screen printing, 5 micromolding in capillaries (MIMIC), 6 inkjet printing, 7 photochemical patterning by photolithography, 8 and microcontact printing through self-assembly monolayer (SAM).9 Recently, we reported micro-scale conducting pattern using the organic soluble PANI substituted with acid-labile tertbutyloxycarbonyl (t-BOC) group on the glass substrate and reversible photochromism between spiropyran (SP) and fluorecein molecules by photolithography.10-14 If this lightregulated reversible uptake and release of protons to SP is combined with the t-BOC-PANI, then the colorimetric change could be controlled by additional stimuli. We report here for the first time the reversible colorimetric change on patterned film of t-BOC-PANI/SP by various stimuli such as photo, thermal, acid/base. Result and DisscussionTo develop for producing patterned images, we tested the possibility of generating micro-patterned images based on the photochromism of t-BOC-PANI/SP system containing triphenylsulfonium triflate (TPSOTf, 5 wt %) as a photo acid generator.The solution of SP and t-BOC-PANI (1:1 molar ratio) was spin-cast to form 1 µm thick films on a glass plate. The film of dark red color was exposed to UV light with 10 mW/cm 2 for 1 min through a photomask without PEB (post-exposure bake) process; noted that t-BOC group of PANI was not completely removed in this process because the deprotection of t-BOC group requires high thermal stress (> 150 o C). Upon additional UV irradiation for one more min, the ME form change into MEH by proton transfer derived from photo acid generator to make an optical microstructure patterning. Thus, the dark red color film before irradiation was changed into bright green color pattern derived from MEH form and t-BOC-PANI at UV irradiated portions as shown in Figure 1 ((a) and (b)). When the film is irradiated with visible right or thermal treatment (50 for 2 min), MEH form completely disappears to SP form switching back to the original color. In this result, this reversible colorimetric change (writing and erasing) is ascribed to sequential chemical reactions of the C-O bond cleavage and C-O bond reformation of SP without deprotecting pathway of t-BOC group of PANI. This localized photochromic process was confirmed by changes in the UV spectra. Figure 2 shows them before (black line of left) and after different doses of UV exposure. The unexposed film displays two absorption bands at 320 and 585 nm, characteristic of undoped EB form of PANI...