Quaterpyridine Ligands for Panchromatic Ru(II) Dye Sensitizers

A new general synthetic access to carboxylated quaterpyridines (qpy), of interest as ligands for panchromatic dye-sensitized solar cell organometallic sensitizers, is presented. The strategic step is a Suzuki-Miyaura cross-coupling reaction, which gave a no. of representative unsubstituted and alkyl and (hetero)arom. substituted qpys. To bypass the poor inherent stability of 2-pyridylboronic acid derivs., the authors successfully applied N-methyliminodiacetic acid (MIDA) boronates as key reagents, obtaining the qpy ligands in good yields up to (quasi) gram quantities. The structural, spectroscopic (NMR and UV-visible), electrochem., and electronic characteristics of the qpy were exptl. and computationally (DFT) studied. The easy access to the bis-thiocyanato Ru(II) complex of the parent species of the qpy series, through an efficient route which bypasses the use of Sephadex column chromatog., is shown. The bis-thiocyanato Ru(II) complex was spectroscopically (NMR and UV-visible), electrochem., and computationally studied, relating its properties to those of previously reported Ru(II)-qpy complexes.