Triplet-triplet annihilation upconversion for calcium sensing

Triplet-triplet annihilation upconversion is a bimolecular process converting low-energy light into high-energy one. All available calcium probes, despite their qualities, are downconverting, which leads to the autofluorescence caused by background emission of the intra- and intercellular molecules. Here we report a calcium-sensing system working via upconverted emission. The probe itself was obtained by covalent conjugation of a perylene blue emitter with a calcium-chelating moiety; it was sensitized by a red-light absorbing palladium porphyrin. Sensing was selective towards Ca2+ and occurred in the micromolar domain in aqueous solutions and methanol. The upconverted luminescence only appeared in the presence of calcium ions, with a quantum yield of up to 0.0018

Coal‐Tar Dye‐based Coordination Cages and Helicates

A strategy to implement four members of the classic coal‐tar dye family, Michler's ketone, methylene blue, rhodamine B, and crystal violet, into [Pd$_2$L$_4$] self‐assemblies is introduced. Chromophores were incorporated into bis‐monodentate ligands using piperazine linkers that allow to retain the auxochromic dialkyl amine functionalities required for intense colors deep in the visible spectrum. Upon palladium coordination, ligands with pyridine donors form lantern‐shaped dinuclear cages while quinoline donors lead to strongly twisted [Pd$_2$L$_4$] helicates in solution. In one case, single crystal X‐ray diffraction revealed rearrangement to a [Pd$_3$L$_6$] ring structure in the solid state. For nine examined derivatives, showing colors from yellow to deep violet, CD spectroscopy discloses different degrees of chiral induction by an enantiomerically pure guest. Ion mobility mass spectrometry allows to distinguish two binding modes. Self‐assemblies based on this new ligand class promise application in chiroptical recognition, photo‐redox catalysis and optical materials

Engineering Soluble Diketopyrrolopyrrole Chromophore Stacks from a Series of Pd(II)-Based Ravels.

Funder: Studienstiftung des Deutschen Volkes; doi: http://dx.doi.org/10.13039/501100004350Funder: Winton Programme for the Physics of SustainabilityFunder: Rowland Institute at Harvard; doi: http://dx.doi.org/10.13039/100009835A strategy to engineer the stacking of diketopyrrolopyrrole (DPP) dyes based on non-statistical metallosupramolecular self-assembly is introduced. For this, the DPP backbone is equipped with nitrogen-based donors that allow for different discrete assemblies to be formed upon the addition of Pd(II), distinguished by the number of π-stacked chromophores. A Pd3 L6 three-ring, a heteroleptic Pd2 L2 L'2 ravel composed of two crossing DPPs (flanked by two carbazoles), and two unprecedented self-penetrated motifs (a Pd2 L3 triple and a Pd2 L4 quadruple stack), were obtained and systematically investigated. With increasing counts of stacked chromophores, UV/Vis absorptions red-shift and emission intensities decrease, except for compound Pd2 L2 L'2 , which stands out with an exceptional photoluminescence quantum yield of 51 %. This is extraordinary for open-shell metal containing assemblies and explainable by an intra-assembly FRET process. The modular design and synthesis of soluble multi-chromophore building blocks offers the potential for the preparation of nanodevices and materials with applications in sensing, photo-redox catalysis and optics

Engineering Soluble Diketopyrrolopyrrole Chromophore Stacks from a Series of Pd(II)‐based Ravels

Funder: Studienstiftung des Deutschen Volkes; doi: http://dx.doi.org/10.13039/501100004350Funder: Winton Programme for the Physics of SustainabilityFunder: Rowland Institute at Harvard; doi: http://dx.doi.org/10.13039/100009835A strategy to engineer the stacking of diketopyrropyrrole (DPP) dyes based on non‐statistical metallosupramolecular self‐assembly is introduced. Therefore, the DPP backbone is equipped with nitrogen‐based donors that allow for different discrete assemblies to be formed upon addition of Pd(II), distinguished by the number of π‐stacked chromophores. A Pd3L6 three‐ring, a heteroleptic Pd2L2L’2 ravel composed of two crossing DPPs (flanked by two carbazoles), and two unprecedented self‐penetrated motifs (a Pd2L3 triple and a Pd2L4 quadruple stack), were obtained and systematically investigated. With increasing counts of stacked chromophores, UV‐Vis absorptions red‐shift and emission intensities decrease, except for compound Pd2L2L’2 which stands out with an exceptional photoluminescence quantum yield of 52%. This is extraordinary for open‐shell metal containing assemblies and explainable by an intra‐assembly FRET process. The modular design and synthesis of soluble multi‐chromophore building blocks opens potential for the preparation of nanodevices and materials with applications in sensing, photo‐redox catalysis and optics.</jats:p

Bifunctional Behavior of a Porphyrin in Hydrogen-Bonded Donor–Acceptor Molecular Chains on a Gold Surface

Peculiar hydrogen-bonded molecular chains are spontaneously created from the self-assembly on a gold surface of a porphyrin functionalized with four aromatic amine moieties. The molecular chains are formed by a sequence of dyads, where the same molecule behaves alternately as a hydrogen-bond acceptor or donor as a whole at all its four aromatic amino groups. This remarkable bifunctional behavior is due to the conformational flexibility of the functionalizing amino groups that switch from a planar, aniline-like conformation in donors to a pyramidal, amine-like one in acceptors. Furthermore, we show that the acceptor porphyrins can trap gold adatoms underneath their center. Combined scanning tunneling microscopy experiments and density functional theory calculations characterize the structural and electronic modifications suffered by such molecules to establish amino 12amino interactions. Notably, scanning tunneling spectroscopy measurements show that the highest occupied molecular orbital 12lowest unoccupied molecular orbital gaps of the acceptors and donors are, respectively, larger and smaller with respect to the isolated molecule according to the reduced extent of conjugation occurring in the acceptors. In summary, experimental and theoretical results reveal a remarkable hydrogen-bonded complex where the amino groups act as both hydrogen-bond donors and acceptors and suggest how hydrogen bonding can modify the geometrical and potentially also the electronic structures of highly conjugated molecules