No abstract

Pursuant to our goal of optimizing the performance of cyclometalated Ru sensitizers in the dye-sensitized solar cell (DSSC), the physicochemical properties of a series of tris-heteroleptic Ru II complexes are reported. Each of these complexes contains a metal ligated by: (i) a bidentate 2,2Ј-bipyridine-4,4Ј-dicarboxylic acid (dcbpy) ligand to anchor the dye to the TiO 2 surface; (ii) a cyclometalating ligand -with electron-withdrawing groups to ensure a sufficiently high oxidation potential for dye regeneration in the DSSC; and

Modifications in the sulfur oxidation state of phenothiazine results in dramatic changes to the excited-state geometry with little effect on the HOMO energy.

The synthesis of two neutral acridone derivatives was carried out to design media sensitive chromophores by taking advantage of intramolecular charge transfer (ICT) features. The molecules comprised two different donor-acceptor-donor triads, with absorption maxima at 425 nm and 520 nm, for the ketone and dicyanomethylene derivatives, respectively. The ketone variant exhibited fluorescence at room temperature, whereas the dicyanomethylene derivative was only emissive in frozen hexane. The ketone emission was highly solvatochromic, with Stokes shifts that ranged from 5000 cm(-1) to 10 000 cm(-1). Electrochemically, both compounds displayed similar oxidation potentials at approximately 0.35 V versus ferrocene/ferrocenium, which was anticipated since both systems employ the same ethynylaniline donor portion of the molecule, whereas only the 9-dicyanomethylene derivative showed a reduction peak at -1.5 V vs. Fc/Fc(+). Additional spectroelectro-chemical experiments supported a delocalized cationic charge on the ethynylaniline fragments during oxidation and that during electrochemical reduction the dicyanomethylene moieties show localized anionic charge. All of the experimental observations are finally compared to DFT, TDDFT and NICS(0) computations to gain insight into the transitions involved and deduce the role of the acridone core in stabilizing its oxidized and reduced forms.