Coordination complexes have been used extensively as the photoactive component of artificial photosynthetic devices. While polynuclear arrays increase the probability of light absorption, the incorporation of the stereogenic Ru(2,2'-bipyridine)(3)(2+) motif gives rise to diastereomeric mixtures whereas the achiral Ru(2,2':6',2"-terpyridine)(2)(2+) motif creates stereopure polynuclear complexes. Thus, polynuclear arrays composed of ruthenium(II) complexes of tridentate ligands are the targets of choice for light-harvesting devices. As Ru(II) complexes of tridentate ligands have short excited state lifetimes at room temperature (r. t.), considerable effort has been focused on trying to increase their r. t. luminescence lifetime for practical applications. This tutorial review will report on the sophisticated synthetic strategies currently in use to enhance the room temperature photophysical properties of Ru(II) complexes of tridentate ligands.

This review article presents the most recent developments in the use of materials based on dipyrromethene (DPM) and azadipyrromethenes (ADPM) for organic photovoltaic (OPV) applications. These chromophores and their corresponding BF2-chelated derivatives BODIPY and aza-BODIPY, respectively, are well known for fluorescence-based applications but are relatively new in the field of photovoltaic research. This review examines the variety of relevant designs, synthetic methodologies and photophysical studies related to materials that incorporate these porphyrinoid-related dyes in their architecture. The main idea is to inspire readers to explore new avenues in the design of next generation small-molecule and bulk-heterojunction solar cell (BHJSC) OPV materials based on DPM chromophores. The main concepts are briefly explained, along with the main challenges that are to be resolved in order to take full advantage of solar energy.

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Artificial photosynthetic systems that contain light-harvesting coordination complexes may one day replace conventional non-renewable sources of energy with renewable solar energy sources. Light-Harvesting Complexes (LHC) are important components of natural photosynthetic systems and are also sought after in artificial systems as well. Polynuclear photoactive complexes are therefore very attractive, and those based on stereogenic [Ru(2,2'-bipyridine)3](2+) are photophysically appealing, but difficult to obtain in a stereochemically pure form. On the other hand, polynuclear complexes based on the achiral [Ru(2,2':6',2''-terpyridine)2](2+) motif are easy to synthesise, however, these complexes are devoid of attractive excited-state properties. Hence strategies to increase the r.t. excited-state lifetime of these complexes would be of practical importance in vectorial electron and/or electron transfer in various optoelectronic applications. This tutorial review will report on the sophisticated synthetic strategies currently in use to enhance the photophysical properties of mononuclear Ru(II) complexes of tridentate ligands at room temperature.

Room-temperature luminescent Co complexes (1 and 2) are presented that exhibit intense ligand-to-metal and ligand-to-ligand charge transfer absorption in the low-energy UV region (λ ≈360-400 nm) and low-negative quasi-reversible reduction events (E =-0.58 V and -0.39 V vs. SCE for 1 and 2, respectively). The blue emission of 1 and 2 at RT is due to the large bite angles and strong σ-donation of the ligands, the combined effect of which helps to separate the emissive LMCT (triplet ligand-to-metal charge transfer) and the non-emissive MC (triplet metal-centered) states. 1 and 2 were found to be powerful photo-oxidants (ECoIII*/CoII =2.26 V and 2.75 V vs. SCE of 1 and 2, respectively) and were used as inexpensive photoredox catalysts for the regioselective mono(trifluoromethylation) of polycyclic aromatic hydrocarbons (PAHs) in good yields (ca. 40-58 %).

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Several ruthenium(II) complexes with new tridentate polypyridine ligands have been prepared, and their photophysical properties have been studied. The new tridentate ligands are tpy-modified systems (tpy = 2,2':6',2' '-terpyridine) in which aromatic substituents designed to be coplanar with the tpy moiety are introduced, with the aim of enhancing delocalization in the acceptor ligand of the potentially luminescent metal-to-ligand charge-transfer (MLCT) state and increasing the MLCT-MC energy gap (MC = metal-centered excited state). Indeed, the Ru(II) complexes obtained with this new family of tridentate ligands exhibit long-lived luminescence at room temperature (up to 200 ns). The enhanced luminescence properties of these complexes support this design strategy and are superior to those of the model Ru(tpy)22+ compound and compare favorably with those of the best Ru(II) complexes with tridentate ligands reported so far.

The synthesis, structural, and photophysical properties of a novel family of neutral fac-[Re(N(∧)N)(CO)(3)(L)] complexes, where N(∧)N is either 2,2'-bipyridine or 1,10-phenanthroline and L is a para functionalized 5-aryltetrazolate [namely, 5-phenyltetrazolate (Tph(-)), 4-(tetrazolate-5-yl)benzaldehyde (Tbdz(-)), 5-(4-acetylphenyl)tetrazolate (Tacy(-)), and methyl 4-(tetrazolate-5-yl)benzoate (Tmeb(-))] are reported. The complexes were prepared by direct addition of the corresponding tetrazolate anion to the acetonitrile solvated fac-[Re(N(∧)N)(CO)(3)](+) precursor. NMR data demonstrate that the coordination of the metal fragment is regiospecific at the N2 atom of the tetrazolate ring. These conclusions are also supported by X-ray structural determinations. Photophysical data were obtained in diluted and deaerated dichloromethane solutions displaying broad and structureless profiles with emission maxima ranging from 566 to 578 nm. The absorption profiles indicate the presence of higher energy intraligand (IL) π-π* transitions and lower energies ligand-to-ligand charge transfer (LLCT) and metal-to-ligand charge transfer (MLCT). As the last two transitions are mixed, they are better described as a metal-ligand-to-ligand charge transfer (MLLCT), a result that is also supported by density functional theory (DFT) calculations. The complexes show excited state lifetime values ranging from 102 to 955 ns, with associated quantum yield between 0.012 and 0.099. Compared to the parent neutral chloro or bromo [Re(N(∧)N)(CO)(3)X], the complexes show a slightly improved performance because of the π accepting nature of the tetrazolato ligand. The metal-to-ligand backbonding is in fact depleting the Re center of electron density, thus widening the HOMO-LUMO gap and reducing the non-radiative decay mechanism in accordance with the energy gap law. Finally, the electron-withdrawing or donating nature of the substituent on the phenyltetrazolato ligand allows the fine-tuning of the photophysical properties.