A theoretical investigation of the dye-redox mediator interaction in dye-sensitized photovoltaic cells

Electrophilicity index revisited

This review aims to be a comprehensive, authoritative, critical, and accessible review of general interest to the chemistry community; because the electrophilicity index is a very useful global reactivity descriptor defined within a conceptual density functional theory framework. Our group has also introduced electrophilicity based new global and local reactivity descriptors and also new associated electronic structure principles, which are important indicators of structure, stability, bonding, reactivity, interactions, and dynamics in a wide variety of physico-chemical systems and processes. This index along with its local counterpart augmented by the associated electronic structure principles could properly explain molecular vibrations, internal rotations and various types of chemical reactions. The concept of the electrophilicity index has been extended to dynamical processes, excited states, confined environment, spin-dependent and temperature-dependent situations, biological activity, site selectivity, aromaticity, charge removal and acceptance, presence of external perturbation through solvents, external electric and magnetic fields, and so forth. Although electrophilicity and its local variant can adequately interpret the behavior of a wide variety of systems and different physico-chemical processes involving them, their predictive potential remains to be explored. An exhaustive review on all these aspects will set the tone of the future research in that direction.

Calculated structural and electronic interactions of the ruthenium dye N3 with a titanium dioxide nanocrystal

Structural and electronic properties of a small anatase TiO2 nanocrystal sensitized by the ruthenium dye N3 (Ru(4,4'-dicarboxy-2,2'-bipyridine)2(NCS)2) have been investigated using density functional theory (DFT) with support from Hartree-Fock (HF) and time dependent DFT (TD-DFT) calculations. Significant structural adjustments of both the dye and the nanocrystal are predicted to be induced by the strain imposed by the simultaneous formation of multiple dye-surface bonds. Electronic properties of the combined dye-nanocrystal system have also been calculated, including information about interfacial orbital mixing and the lowest excited singlet states. Ultrafast photoinduced electron transfer processes across the dye-nanoparticle interface in dye-sensitized solar cells are finally discussed in view of estimated electronic coupling strengths. The calculations predict injection times on the order of 10 fs for MLCT excitations to the ligand pi* levels that interact most strongly with the TiO2 conduction band, and an order of magnitude increase in the injection times for excitations to dye levels with poor spatial or energetic overlaps with the substrate conduction band.

Electronic Structures and Absorption Spectra of Linkage Isomers of Trithiocyanato (4,4‘,4‘ ‘-Tricarboxy-2,2‘:6,2‘ ‘-terpyridine) Ruthenium(II) Complexes: A DFT Study

Black dye (BD), isomer 1 ([Ru(II)(H3-tctpy)(NCS)3](-1), where H3-tctpy = 4,4',4' '-tricarboxy-2,2':6,2' '-terpyridine) is known to be an excellent sensitizer for dye-sensitized solar cells and exhibits a very good near-IR photo response, compared to other ruthenium dyes. Because isothiocyanate is a linear ambidentate ligand, BD has three other linkage isomers, [Ru(H3-tctpy)(NCS)2(SCN)](-1), isomer 2 and 2', and [Ru(H3-tctpy))(SCN)3](-1), isomer 3. In this study, we have calculated the geometry of BD and its isomers by DFT. Further, we have analyzed the bonding in these isomers using NBO methods. TDDFT calculations combined with scalar relativistic zero-order regular approximations (SR-ZORA) have been carried out to simulate the absorption spectra. Calculations have been performed for the isomers both in vacuo and in solvent (ethanol). The inclusion of the solvent is found to be important to obtain spectra in good agreement with the experiment. The first absorption bands are dominated by the metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT).