Two new heterotrinuclear Fe-Ru-Fe complexes of ruthenium(II) tetraphenylporphyrin axially coordinated with a pair of isocyanoferrocene ((FcNC)2RuTPP, 1) or 1,1'-diisocyanoferrocene (([C5H4NC]2Fe)2RuTPP, 2) ligands [Fc = ferrocenyl, TPP = 5,10,15,20-tetraphenylporphyrinato(2-) anion] were synthesized and characterized by UV-vis, magnetic circular dichroism, NMR, and FTIR spectroscopies as well as by electrospray ionization mass spectrometry and single-crystal X-ray diffraction. Isolation of insoluble polymeric {([C5H4NC]2Fe)RuTPP}n molecular wires (3) was also achieved for the first time. The redox properties of the new trinuclear complexes 1 and 2 were probed using electrochemical (cyclic voltammetry and differential pulse voltammetry), spectroelectrochemical, and chemical oxidation methods and correlated to those of the bis(tert-butylisocyano)ruthenium(II) tetraphenylporphyrin reference compound, (t-BuNC)2RuTPP (4). In all cases, the first oxidation process was attributed to the reversible oxidation of the Ru(II) center. The second and third reversible oxidation processes in 1 are separated by ∼100 mV and were assigned to two single-electron Fe(II)/Fe(III) couples, suggesting a weak long-range iron-iron coupling in this complex. Electrochemical data acquired for 2 are complicated by the interaction between the axial η(1)-1,1'-diisocyanoferrocene ligand and the electrode surface as well as by axial ligand dissociation in solution. Spectroelectrochemical and chemical oxidation methods were used to elucidate the spectroscopic signatures of the [1](n+), [2](n+), and [4](n+) species in solution. DFT and time-dependent DFT calculations aided in correlating the spectroscopic and redox properties of complexes 1, 2, and 4 with their electronic structures.

A unique combination of two independent mechanisms of fluorescence quenching, namely intramolecular charge transfer (ICT) from a peripheral donor and protonation of azomethine nitrogen atoms in zinc tetrapyrazinoporphyrazines (TPyzPz), provides a new possibility for sensing pH in a specific range. The pH selectivity was controlled by the different basicities of the donor for ICT (dimethylaminoaryl), which was connected to the macrocycle by π-extended linkers of different lengths. ICT and protonation have been studied in detail by photophysical, spectral (UV/Vis and MCD spectra), and electrochemical measurements, and further supported by theoretical calculations (DFT, TDDFT). The pH-sensing properties of the TPyzPzs have been investigated in THF and in water after anchoring the TPyzPzs to liposomes. The salient pK values were around 1.3 (azomethine nitrogen) and 2.29-4.76 (donor for ICT). The lead indicators (sensing over a pH range of 1.0-2.5) with fairly steep sensing profiles exhibited increases in fluorescence between the OFF/ON states of more than 20-fold and strong absorption in the red region (Q-band maximum >650 nm, ϵ≈2×10 m cm ).

The excited-state dynamics and energetics of a series of BODIPY-derived chromophores bound to a catechol at the boron position were investigated with a combination of static and time-resolved spectroscopy, electrochemistry, and density functional theory calculations. Compared with the difluoro-BODIPY-derived parent compounds, the addition of the catechol at the boron reduced the excited-state lifetime by three orders of magnitude. Deactivation of the excited state proceeded through an intermediate charge-transfer state accessed from the initial optically excited π* state in <1 ps. Despite differences in the structures of the BODIPY derivatives and absorption maxima that spanned the visible portion of the spectrum, all compounds exhibited the same, rapid, excited-state deactivation mechanism, suggesting the generality of the observed dynamics within this class of compounds.

Two spherical organic−inorganic ferrocene-tin (hydr)oxide clusters of general formula [(FcSn) 12 O 14 (OH) 6 ]X 2 (Fc = ferrocenyl, X = nitroso-dicyanmethanide, DCO − and benzoylcyanoxime, PCO − anions) were prepared by the direct hydrolysis of Fc 2 SnCl 2 or FcSnCl 3 precursors in the presence of light-and thermally stable Ag(DCO) or Ag(PCO) salts. Molecular structures of FcSnCl 3 Py 2 (1), Fc 2 SnCl 2 Py 2 (2), [(FcSn) 12 O 14 (OH) 6 ](DCO) 2 (3), and [(FcSn) 12 O 14 (OH) 6 ](PCO) 2 (4) were investigated by X-ray crystallography. Density function theory (DFT) and time-dependent density functional theory (TDDFT) calculations were conducted on FcSnCl 3 Py 2 , Fc 2 SnCl 2 Py 2 , and [(FcSn) 12 O 14 (OH) 6 ] 2+ compounds in order to elaborate electronic structures and assign transitions in UV−vis spectra of these systems. The DFT and TDDFT calculations suggest that the organometallic substituents in the [(FcSn) 12 O 14 (OH) 6 ] 2+ core are rather isolated from each other.

Two isomeric ruthenium(II) 5,10,15,20-tetraphenylporphyrins axially coordinated to the redoxactive, low-optical gap-containing 2-or 6-isocyanoazulene ligands have been prepared and characterized by NMR, UV-vis, and MCD spectroscopy methods, high-resolution mass spectrometry, and X-ray crystallography. The UV-vis and MCD spectra are suggestive of the presence of the low-energy, azulene-centered transitions in the Q-band region of the porphyrin chromophore. The first coordination sphere in new L2RuTPP complexes is reflective of compressed tetragonal geometry. The redox properties of the new compounds were studied by electrochemical and spectroelectrochemical methods and correlated with the electronic structures predicted by the Density Functional Theory calculations. The experimental and theoretical data are suggestive of the low-potential reduction processes centred at the axial azulene ligands and oxidation processes centred at the ruthenium ion or porphyrin core.

Two switches are shown to control the fluorescence in an efficient red‐emitting fluorescent indicator with a steep sensing profile. Intramolecular charge transfer from the peripheral tertiary amine and protonation of azomethine nitrogen atoms in azaphthalocyanine are involved in the sensing mechanism. The particular pH range is driven by the basicity of these two centers and can be simply tuned by structural changes in the molecule. More information can be found in the Full Paper by V. Nemykin, P. Zimcik, V. Novakova et al. on page 1795 ff.

Invited for the cover of this issue are the groups of Victor Nemykin (University of Manitoba), and Petr Zimcik and Veronika Novakova (Charles University in Prague). The image depicts how tetrapyrazinoporphyrazines can be controlled by two switches. Read the full text of the article at 10.1002/chem.201604978.