Synthesis and electronic properties of 3-acceptor-substituted and 3,7-bisacceptor-substituted phenothiazines

3-Acceptor-substituted and 3,7-bisacceptor-substituted phenothiazines can be synthesized in moderate to excellent yields through Suzuki cross-coupling reactions between phenothiazin-3-yl pinacolyl boronates or phenothiazin-3,7-diyl bis(pinacolyl boronates) and electron-deficient (hetero)aryl halides. The electronic properties of (hetero) aryl-substituted N-methyl phenothiazines (UV/Vis absorption fluorescence, redox potentials) can be correlated with the computed energies of the frontier molecular orbitals. Nitro-substituted derivatives reveal electronically amphoteric behavior, displaying both reversible oxidations and reversible reductions. X-ray structure analysis of the phenothiazinyl p-(2,5-dinitro)phenylene-bridged dyad 13 revealed donor-acceptor interactions between the molecules. Pyridyl and pyrimidyl derivatives fluoresce with quantum yields (phi(f)) of up to 49% and can be regarded as redox-active fluorophores. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).