Molecular engineering for optical properties of 5-substituted-1,10-phenanthroline-based Ru(II) complexes

A series of homo- and heteroleptic Ru(ii) complexes [Ru(phen)3-n(phen-X)n](PF6)2 (n = 0-3, X = CN, epoxy, H, NH2) were prepared and characterized. The influence of electron-withdrawing or electron-releasing substituents of the 1,10-phenanthroline ligands on the photo-physical properties was evaluated. It reveals fundamental interests in the fine tuning of redox potentials and photo-physical characteristics, depending both on the nature of the substitution of the ligand, and on the symmetry of the related homo- or heteroleptic complex. These complexes exhibit linear absorption and two-photon absorption (2PA) cross-sections over a broad range of wavelength (700-900 nm) due to absorption in the intra-ligand charge transfer (ILCT) and the metal-to-ligand charge transfer (MLCT) bands. These 2PA properties were more particularly investigated in the 700-1000 spectral range for a family of complexes bearing electro-donating ligands (phen-NH2).

High sensitivity fluorescence up-conversion spectroscopy of 3MLCT emission of metal-organic complexes

We demonstrate the implementation of a broadband fluorescence up-conversion set-up with high signal-to-noise ratio and dynamic range allowing for the detection of weak luminescence from triplet states in Fe(II) NHC complexes. Based on the experimentally determined radiative rates and the emission spectra, these states have dominant MLCT character.

Iron(ii) complexes with diazinyl-NHC ligands: impact of π-deficiency of the azine core on photophysical properties

Boosting iron(ii) complex excited-state lifetime by combining pyrazine and benzimidazolylidene NHC ligands.

Single-crystal X-ray diffraction study, NMR and electrochemical analysis of a copper(i) 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis-[(6-methyl-2,2′-bipyridyl-6-yl)methoxy]calix[4]arene complex: an original M4L2“hand-to-hand” system

An original M₄L₂“hand-to-hand” copper(i)/tetra-bipyridyl-calix[4]arene complex was obtained and characterized in the solid state by X-ray diffraction. It changes in MeCN solution to its M₂L analogue.

Synthesis and Computational Study of a Pyridylcarbene Fe(II) Complex: Unexpected Effects of fac/ mer Isomerism in Metal-to-Ligand Triplet Potential Energy Surfaces

The synthesis and the steady-state absorption spectrum of a new pyridine-imidazolylidene Fe(II) complex (Fe-NHC) are presented. A detailed mechanism of the triplet metal-to-ligand charge-transfer states decay is provided on the basis of minimum energy path (MEP) calculations used to connect the lowest-lying singlet, triplet, and quintet state minima. The competition between the different decay pathways involved in the photoresponse is assessed by analyzing the shapes of the obtained potential energy surfaces. A qualitative difference between facial ( fac) and meridional ( mer) isomers' potential energy surface (PES) topologies is evidenced for the first time in iron-based complexes. Indeed, the mer complex shows a steeper triplet path toward the corresponding ³MC minimum, which lies at a lower energy as compared to the fac isomer, thus pointing to a faster triplet decay of the former. Furthermore, while a major role of the metal-centered quintet state population from the triplet ³MC region is excluded, we identify the enlargement of iron-nitrogen bonds as the main normal modes driving the excited-state decay.

A new record excited state 3MLCT lifetime for metalorganic iron(ii) complexes

The ³MLCT lifetime of iron complexes was pushed to a record lifetime of 26 ps using a new benzimidazolylidene-based C^∧N^∧C ligand opening up new perspectives on the way of applying such complexes to photoelectrochemical processes.

A study of the impact of co-adsorbents on DSSC electron transfer processes: anti-π-stacking vs. shield effect

In this study we report a detailed exploration of the use of two different co-adsorbents – namely bis-methoxyphenylphosphinic acid (BMPP) and chenodeoxycholic acid (CDCA) – known to increase photoconversion efficiency (PCE) of DSSCs sensitized with N719.

2,5-Dithienylpyrrole (DTP) as a donor component in DTP–π–A organic sensitizers: photophysical and photovoltaic properties

DTP–π–A organic dyes efficiently sensitized TiO₂ in DSSCs exhibiting nearly quantitative charge injection yields and regeneration efficiency.

Theoretical study of new ruthenium-based dyes for dye-sensitized solar cells

Two relevant, recently reported, ruthenium-based complexes to be used as sensitizers in Grätzel photovoltaic cells are theoretically studied. The UV/vis absorption spectra have been computed within the time-dependent density functional theory formalism. The obtained excitation energies are compared with the experimental results, and the nature of the transition is analyzed in terms of the electronic density. A preliminary study on the performance of different functionals against the equation of motion coupled cluster is performed on a smaller model system.

Tuning of Ruthenium Complex Properties Using Pyrrole- and Pyrrolidine-Containing Polypyridine Ligands

The effect of pyrrole- and pyrrolidine-containing ligands (L) on the properties of heteroleptic [RuL2dcbpy]2+ complexes has been investigated. TiO2 electrodes modified with the new complexes exhibited extended absorption domains and high absorbances. Providing that a cobalt-based mediator was used for regeneration of the RuII state, good incident photon-to-current efficiency (near 80%) values were obtained in the pyrrole series.

Pyrrolidine-Containing Polypyridines: New Ligands for Improved Visible Light Absorption by Ruthenium Complexes

[reaction: see text] A range of new electron-releasing pyrrolidine-containing bipyridines and terpyridines has been prepared via selective metalation-cross-coupling sequences. The obtained ligands have been involved in microwave-assisted ruthenium complexation leading to homoleptic complexes in high yield. The electron-donor effect of the pyrrolidine nucleus led to a notable improvement of visible light absorption and strong changes in the electrochemical behavior, opening new opportunities for the design of photovoltaic devices.

Energy Transfer in Rigid Ru(II)/Os(II) Dinuclear Complexes with Biscyclometalating Bridging Ligands Containing a Variable Number of Phenylene Units

We have prepared rodlike cyclometalated Ru(II)/Os(II) dinuclear complexes, (ttp)Ru(dpb-(ph)(n)()-dpb)Os(ttp)(2+), where the biscyclometalating bridging ligands contain dipyridylbenzene fragments, dbp, separated by a variable number, n, of phenylene spacers, and the terminal ligand is a terpyridine derivative [dpbH is di-2-pyridyl-1,3-benzene, ttp is 4'-p-tolyl-2,2':6',2"-terpyridine, and n = 0-2]. The rigid bridging ligands keep the metal centers at a distance r(MM) = 11, 15.5, and 20 Å, depending on n. Photoinduced energy transfer has been investigated by luminescence spectroscopy in nitrile solvents at room temperature and at 77 K (i.e., in frozen medium). According to a classical description of the process, the energy transfer occurs in a nearly activationless regime, is governed by electronic factors, and can be described in terms of the Dexter-type mechanism. The obtained energy transfer rates roughly span 3 orders of magnitude and indicate (i) that the temperature (i.e., the state of the solvent) has a small influence on the process and (ii) that the interposed phenylene spacers are weak attenuators of intercenter electronic coupling, H [H = H(0) exp(-betar(MM)), with beta approximately 0.33 Å(-)(1)].