5-(Hetero)aryl-Substituted 9-Hydroxyphenalenones: Synthesis and Electronic Properties of Multifunctional Donor-Acceptor Conjugates

5-(Hetero) aryl-substituted 9-hydroxyphenalenones (9-HP) can be readily synthesized by Suzuki coupling of 5-bromo 9-HP with (hetero) aryl boronic acid (derivatives) without protection of the hydroxyl functionality in moderate to excellent yields (57-94%). A library of 5-(hetero) aryl substituted 9-HP with broad substituent variation was studied with respect to their electronic properties (absorption and emission spectroscopies and cyclic voltammetry) and their computed electronic structures. All compounds show reversible reductive potentials between -1230 and -1110 mV and the donor-substituted representatives possess irreversible oxidation potentials around 600 mV. Compounds with electron-rich donors even show reversible oxidation potentials. Especially the donor-substituted 9-HPs display emission bands between 466 and 567 nm with quite large Stokes shifts (up to 4100 cm(-1)). TD-DFT calculations nicely reproduce the spectroscopic data and Hammett correlations underline a pronounced resonance substituent influence on the photophysical properties.