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A hexylalkoxy dipolar D–A–A molecule [7-(4-N,N-(bis(4-hexyloxyphenyl)amino)phenyl)-2,1,3-(benzothia-diazol-4-yl)methylene]propane-dinitrile, (C6-TPA-BT-CN) has been synthesized and the photophysics studied via femtosecond transient absorption spectroscopy (FsTA) in toluene and in amorphous and liquid crystalline spherulite thin films. Two spherulite macromolecular crystalline phases (banded, and non-banded) were observed through concentration dependent, solution processing techniques and are birefringent with a negative sign of elongation. A dramatic change in the electronic absorption from blue in amorphous films to green in spherulites was observed, and the molecular orientation was determined through the combined analysis of polarized light microscopy, X-ray diffraction, and scanning electron microscopy. FsTA was performed on amorphous films and show complex charge recombination dynamics, and a Stark effect, characterized from the combined TPA+Ṗ and [BT-CN]−Ṗ spectroscopic signatures at 450 nm and 510 nm and identified through spectroelectrochemistry. Radical cation dynamics of TPA+Ṗ was observed selectively at 750 nm with ＞503.3 ps (18%) recombination kinetics resulting in a rather significant yield of free charge carriers in amorphous films and consistent with previous reports on energetically disordered blend films. However, photoexcitation on large, non-banded spherulites areas (＞250 μm) reveal average monoexponential charge recombination lifetimes of 169.2 ps from delocalized states similar to those observed in amorphous films and are 5× longer-lived than previous reports [Chang et al., J. Am. Chem. Soc., 2013, 135, 8790] of a related methyl-DPAT-BT-CN whose amorphous thin films were prepared through vapor deposition. Thus, the correlation between the microstructure of the blend film and the photoinduced radical pair dynamics described here is critical for developing a fundamental understanding of how dipolar states contribute to the charge carrier yield in a disordered energy system. [ABSTRACT FROM AUTHOR]

Multi-metallic complexes based on {Ru–Cr}, {Ru–Ru} and {Ru–Ru–Cr} fragments are investigated for their light-harvesting and long-range energy transfer properties. We report the synthesis and characterization of [Ru(tpy)(bpy)(μ-CN)Ru(py)4Cl]2+ and [Ru(tpy)(bpy)(μ-CN)Ru(py)4(μ-NC)Cr(CN)5]. The intercalation of {RuII(py)4} linked by cyanide bridges between {Ru(tpy)(bpy)} and {Cr(CN)5} results in efficient, distant energy transfer followed by emission from the Cr moiety. Characterization of the energy transfer process based on photophysical and ultrafast time-resolved absorption suggests the delocalization of holes in the excited state, providing a pathway for energy transfer between the end moieties. The proposed mechanism opens the door to utilize this family of complexes as an appealing platform for the design of antenna compounds as the properties of the fragments could be tuned independently. [ABSTRACT FROM AUTHOR]

A series of cyanide-bridged bimetallic compounds of the general formula [Ru(L)(bpy)(μ-NC)(M)]2−/−/2+ (L = tpy, 2,2′-6′,2′′-terpyridine, or tpm, tris(1-pyrazolyl)methane, bpy = 2,2′-bipyridine, M = RuII(CN)5, OsIII(CN)5, OsII(CN)5, RuII(py)4(CN), py = pyridine) have been synthesized and fully characterized. Most of them present MLCT emission (λ = 690–730 nm, Φ = 10−3–10−4) and their photophysical properties resemble the ones of the respective mononuclear Ru(L)(bpy) species. The exception is when M is OsIII(CN)5, where an intramolecular electron transfer quenching mechanism is proposed. The conditions that should be met for avoiding the reductive or oxidative quenching of the excited state are also discussed. [ABSTRACT FROM AUTHOR]

We report the synthesis, structure and properties of the cyanide-bridged dinuclear complex ions [Ru(L)(bpy)(μ-NC)M(CN)(5)](2-/-) (L = tpy, 2,2';6',2''-terpyridine, or tpm, tris(1-pyrazolyl)methane, bpy = 2,2'-bipyridine, M = Fe(II), Fe(III), Cr(III)) and the related monomers [Ru(L)(bpy)X](2+) (X = CN(-) and NCS(-)). All the monomeric compounds are weak MLCT emitters (λ = 650-715 nm, ϕ ≈ 10(-4)). In the Fe(II) and Cr(III) dinuclear systems, the cyanide bridge promotes efficient energy transfer between the Ru-centered MLCT state and a Fe(II)- or Cr(III)-centered d-d state, which results either in a complete quenching of luminescence or in a narrow red emission (λ ≈ 820 nm, ϕ ≈ 10(-3)) respectively. In the case of Fe(III) dinuclear systems, an electron transfer quenching process is also likely to occur.