Ethylthio-substituted sandwich phthalocyaninato europium (III) semiconductors for sensing NO2 and NH3: Effect of the extended π-conjugate systems on tuning the conductivity and sensing behavior

• Published in: Organic electronics 2021-06, Vol.93, p.106151, Article 106151
• Main Authors: Wei, Chuangyu, Lu, Guang, Guo, Chang, Lv, Xuehui, Tang, Xiangjie, Liu, Qi, Cai, Xue, Chen, Yanli, Jiang, Jianzhuang
• Format: Article
• Language: English
• Subjects: Gas sensing; Organic semiconductor; Sandwich-type phthalocyanine; Solution-processed film; π-conjugate system
• ISSN: 1566-1199; 1878-5530
• DOI: 10.1016/j.orgel.2021.106151

By using the π-conjugated phthalocyanine macrocycle as the versatile building block, a series of five sandwich-type ethylthio substituted phthalocyaninato europium complexes, namely double-decker Eu[Pc(SC2H5)8]2 (Pc-1), triple-decker Eu2[Pc(SC2H5)8]3 (Pc-2), and their corresponding dimers, [Pc(SC2H5)8]2Eu2[BiPc(SC2H5)12] (Pc-1@Pc-1), [Pc(SC2H5)8]3Eu3[BiPc(SC2H5)12] (Pc-1@Pc-2) and [Pc(SC2H5)8]4Eu4[BiPc(SC2H5)12] (Pc-2@Pc-2), are synthesized and prepared into the solution-processed films by a simple quasi-Langmuir-Shäfer (QLS) method. Combination between the extending π-conjugated system in the longitudinal and transverse directions of Pc macrocycles and/or radical nature of Pc-1 unit among different semiconducting molecules result in unusually small energy gaps (0.345–0.91 eV). Consequently, all of the semiconductors exhibit excellent conductivities. Among these materials, the conductivity for the radical species Pc-1@Pc-1, Pc-1@Pc-2 and Pc-1 is about 3–4 times larger than that for the non-radical compounds Pc-2@Pc-2 and Pc-2. Moreover, the QLS films of five semiconductors take excellent linear responses for both oxidizing NO2 (100–300 ppb) and reducing NH3 (4–8.6 ppm). Respectively, the sensitivity (in % ppm−1) gets increased in the order of Pc-1