MDPI Acta Medica Okayama 1420-3049 25 17 2020 Synthesis and Physicochemical Properties of 2,7-Disubstituted Phenanthro[2,1-b:7,8-b']dithiophenes 3842 EN Zhenfei Ji Graduate School of Natural Science and Technology, Okayama University Zeliang Cheng Graduate School of Natural Science and Technology, Okayama University Hiroki Mori Research Institute for Interdisciplinary Science, Okayama University Yasushi Nishihara Research Institute for Interdisciplinary Science, Okayama University We report the design, synthesis, and physicochemical properties of an array of phenanthro[2,1-b:7,8-b']dithiophene (PDT-2) derivatives by introducing five types of alkyl (CnH2n+1; n = 8, 10, 12, 13, and 14) or two types of decylthienyl groups at 2,7-positions of the PDT-2 core. Systematic investigation revealed that the alkyl length and the type of side chains have a great effect on the physicochemical properties. For alkylated PDT-2, the solubility was gradually decreased as the chain length was increased. For instance, C-8-PDT-2 exhibited the highest solubility (5.0 g/L) in chloroform. Additionally, substitution with 5-decylthienyl groups showed poor solubility in both chloroform and toluene, whereas PDT-2 with 4-decylthienyl groups resulted in higher solubility. Furthermore, UV-vis absorption of PDT-2 derivatives substituted by decylthienyl groups showed a redshift, indicating the extension of their pi-conjugation length. This work reveals that modification of the conjugated core by alkyl or decylthienyl side chains may be an efficient strategy by which to change the physicochemical properties, which might lead to the development of high-performance organic semiconductors. No potential conflict of interest relevant to this article was reported.