Photoinduced Energy- and Electron-Transfer Processes in a Side-to-Face Ru -Porphyrin/Perylene-bisimide Array.

A side-to-face array DPy-gPBI[Ru(4-tBuTPP)(CO)] , based on a "green" perylene bisimide chromophore sandwiched between two Ru -porphyrins, has been prepared by self-assembly. Its photophysical properties have been characterized in detail by a combination of steady-state and time-resolved techniques upon selective excitation of the two different components. Different photoinduced processes are observed as a function of the excitation wavelength.

Sn(IV) Multiporphyrin Arrays as Tunable Photoactive Systems.

A series of four arrays made of a central Sn(IV) porphyrin as scaffold axially connected, via carboxylate functions, to two free-base porphyrins has been prepared and fully characterized. Three arrays in the series feature the same free-base unit and alternative tin-porphyrin macrocycles, and one consists of a second type of free-base and one chosen metallo-porphyrin. A thorough photophysical investigation has been performed on all arrays by means of time-resolved emission and absorption techniques.

Self-Assembled Ruthenium(II)Porphyrin-Aluminium(III)Porphyrin-Fullerene Triad for Long-Lived Photoinduced Charge Separation.

A very efficient metal-mediated strategy led, in a single step, to a quantitative construction of a new three-component multichromophoric system containing one fullerene monoadduct, one aluminium(III) monopyridylporphyrin, and one ruthenium(II) tetraphenylporphyrin. The Al(III) monopyridylporphyrin component plays the pivotal role in directing the correct self-assembly process and behaves as the antenna unit for the photoinduced processes of interest. A detailed study of the photophysical behavior of the triad was carried out in different solvents (CHCl, THF, and toluene) by stationary and time-resolved emission and absorption spectroscopy in the pico- and nanosecond time domains.

Zinc porphyrin-Re(I) bipyridyl-fullerene triad: synthesis, characterization, and kinetics of the stepwise electron-transfer processes initiated by visible excitation.

A new triad system featuring one zinc porphyrin and one fullerene moieties attached to a central redox-active Re(I) connector was obtained in remarkable yield by cleverly exploiting a facile two-step synthesis. Detailed description and discussion on the characterization of this multicomponent system and of its parent free-base analogue are presented, along with a kinetic study of the stepwise electron-transfer processes occurring upon visible excitation.

On the effect of the nature of the bridge on oxidative or reductive photoinduced electron transfer in donor-bridge-acceptor systems.

Photoinduced electron transfer is a topical issue in chemistry. In multicomponent donor-bridge-acceptor systems, electron transfer is usually discussed within the frame of superexchange theory, which takes into account electronic coupling mediated by virtual states involving bridge orbitals. However, the schematization used for superexchange in thermal electron transfer processes is not suitable to immediately understand some intriguing aspects of photoinduced charge separation and recombination processes, which are only uncovered by analyzing the virtual states involved in forward and backward excited-state electron transfer.

Improving the efficiency of the photoinduced charge-separation process in a rhenium(I)-zinc porphyrin dyad by simple chemical functionalization.

We demonstrate here that, whereas the rhenium(I)-zinc porphyrin dyad fac-[Re(CO)3(bpy)(Zn·4'MPyP)](CF3SO3) [1; 4'MPyP = 5-(4'-pyridyl)-10,15,20-triphenylporphyrin] shows no evidence for photoinduced electron transfer upon excitation in the visible region because the charge-separated state ZnP(+)-Re(-) is almost isoenergetic with the singlet excited state of the zinc porphyrin (ΔG = -0.05 eV), the introduction of electron-withdrawing ethyl ester groups on the bpy ligand significantly improves the thermodynamics of the process (ΔG = -0.42 eV).

Synthesis and properties of phosphorescent iridium(III) complexes of delocalized ligands.

New Ir(III) complexes involving N,C-chelating difluorophenyl-pyridine (dfppy) or dibenzo[a,c]phenazine (dbpz) ligands along with either N,N-bound 5-ethynyl-2,2'-bipyridine (e-bpy) or CO + Cl co-ligands have been obtained as [Ir(dfppy)(2)(e-bpy)]PF(6), [Ir(dbpz)(2)(e-bpy)]PF(6) and cis-[Ir(dbpz)(2)(Cl)(CO)]. A single-crystal X-ray diffraction study of cis-[Ir(dbpz)(2)(CO)Cl] has shown the Ir(III) centre to adopt a distorted octahedral coordination geometry with cis-CO/Cl and trans-N,N configurations. Pronounced π-π stacking interactions involving different dibenzo[a,c]phenazine units are evident.

Electron transfer across modular oligo-p-phenylene bridges in Ru(bpy)2(bpy-ph(n)-DQ)4+ (n = 1-5) dyads. Unusual effects of bridge elongation.

A series of dyads of general formula Ru(bpy)(2)(bpy-ph(n)-DQ)(4+) (n = 1-5), based on a Ru(II) polypyridine unit as photoexcitable donor, a set of oligo-p-phenylene bridges with 1-5 modular units, and a cyclo-diquaternarized 2,2'-bipyridine (DQ(2+)) as electron acceptor unit, have been synthesized. Their spectroscopic and photophysical properties have been investigated in CH(3)CN and CH(2)Cl(2) by time-resolved emission and absorption spectroscopy in the nanosecond and picosecond time scale. The experimental study has also been complemented with a computational investigation carried out on the whole series of dyads.

Concerted motions in supramolecular systems: metal-mediated assemblies of porphyrins that behave like nanometric step-machines.

According to NMR evidence the metal-mediated sandwich assemblies of porphyrins 2 and 3 undergo in solution a thermally driven motion that resembles that of a stepper: the spontaneous rotational motion of the pyridyl rings is converted into a reciprocating linear motion of the porphyrins.

Triplet pathways in diarylethene photochromism: photophysical and computational study of dyads containing ruthenium(II) polypyridine and 1,2-bis(2-methylbenzothiophene-3-yl)maleimide units.

A 1,2-bis(2-methylbenzothiophene-3-yl)maleimide model ( DAE) and two dyads in which this photochromic unit is coupled, via a direct nitrogen-carbon bond ( Ru-DAE) or through an intervening methylene group ( Ru-CH 2-DAE ), to a ruthenium polypyridine chromophore have been synthesized. The photochemistry and photophysics of these systems have been thoroughly characterized in acetonitrile by a combination of stationary and time-resolved (nano- and femtosecond) spectroscopic methods. The diarylethene model DAE undergoes photocyclization by excitation at 448 nm, with 35% photoconversion at stationary state.

Photoinduced electron transfer across oligo-p-phenylene bridges. Distance and conformational effects in Ru(II)-Rh(III) dyads.

A series of rodlike ruthenium(II)-rhodium(III) polypyridine dyads based on modular oligo-p-phenylene bridges, of the general formula [(Me2phen)2Ru-bpy-(ph)n-bpy-Rh(Me2bpy)]5+ (Me2phen=4,7-dimethyl-1,10-phenanthroline; bpy=2,2'-bipyridine; ph=1,4-phenylene; n=1-3), have been synthesized and their photophysical properties investigated. The dyad [(Me2bpy)2Ru-bpy-(ph)3'-bpy-Rh(Me2bpy)]5+ with the central phenylene unit bearing two hexyl chains has also been studied. The metal-to-metal distance reaches 24 A for the longest (n=3) spacer in the series.

Design of Long-Lived Ru(II) Terpyridine MLCT States. Tricyano Terpyridine Complexes.

The photophysics of Ru(tpy)(CN)(3)(-) and Ru(ttpy)(CN)(3)(-) (where tpy = 2,2':6',2"-terpyridine and ttpy = 4'-(p-tolyl)-2,2':6,2"-terpyridine) has been studied in detail. The complexes exhibit strongly solvatochromic behavior. Emission energies correlate linearly with solvent acceptor number, consistent with the metal-to-ligand charge transfer (MLCT) nature of the emission and the occurrence of second-sphere donor-acceptor interactions at the cyanide ligands.

Photophysics of Supercomplexes. Adduct between Ru(bpy)(CN)(4)(2-) and the [32]ane-N(8)H(8)(8+) Polyaza Macrocycle.

The formation of a supercomplex between the Ru(bpy)(CN)(4)(2-) (bpy = 2,2'-bipyridine) complex and the [32]ane-N(8)H(8)(8+) macrocycle (1) has been studied in water and in acetonitrile. In acetonitrile, supercomplex formation is accompanied by (i) large hypsochromic shifts in the absorption spectrum (color changes from deep violet to yellow) and in the emission spectrum, (ii) large anodic shifts in standard oxidation (0.73 V) and reduction (0.

Photoinduced Electron and Energy Transfer in Rigidly Bridged Ru(II)-Rh(III) Binuclear Complexes.

A series of binuclear Ru(II)-Rh(III) complexes of general formula (ttpy)Ru-tpy-(ph)(n)-tpy-Rh(ttpy)(5+) (n = 0-2) have been synthesized, where ttpy = 4'-p-tolyl-2,2':6,2"-terpyridine and tpy-(ph)(n)-tpy represents a bridging ligand where two 2,2':6',2"-terpyridine units are either directly linked together (n = 0) or connected through one (n = 1) or two (n = 2) phenyl spacers in the 4'-position. This series of complexes is characterized by (i) rigid bridge structures and (ii) variable metal-metal distances (11 Å for n = 0, 15.5 Å for n = 1, 20 Å for n = 2).