Synthesis of hydroxyoligophenylenes containing electron-donating, electron-accepting groups, or π-deficient aromatic ring and their solvatochromic behavior

Abstract

We have reported oligo(p-phenylene)s (OPPs) with an OH group located at one end, namely, OPP(n)-OHs (where n is the number of benzene rings). The OPPs exhibited significant solvatochromism; the deprotonation of the OH groups of OPP(n)-OHs, when treated with NaH, caused a bathochromic shift of absorption maxima (λmax) that increased with the donor numbers (DNs) of the solvents. We assumed that the solvatochromism exhibited by OPP(n)-ONa was attributed to an intramolecular charge shift from the sodium phenoxy group(s) to the adjacent rings. In this study, to investigate the assumption, hydroxyoligophenylenes (R-OPP(n)-OH) with an electron-donating dimethylamino group (n = 3, R = NMe2), an electron-accepting nitro group (n = 3, R = NO2), and a π-deficient pyridine ring (n = 2, R = Py) were synthesized by the Suzuki coupling reaction. The deprotonation of the OH group of by treatment with NaH caused a bathochromic shift (Δλ) of λmax of R-OPP(m)-ONa. The Δλ of the deprotonated species increased with the DNs of the solvents. The emission peak positions of R-OPP(m)-ONa depended on the DNs of the solvents; therefore, the emission color could be tuned by changing the solvent. R-OPP(m)-OH received an electrochemical oxidation of the OH group and OPP unit. The data related to the remarkable solvatochromic behavior of R-OPP(n)-ONa will be useful information for the development of new luminescent materials.