The two sp(3) hybridized fluorine atoms of a Bodipy dye have been synthetically replaced with the linear donor ligand 4-ethynylpyridine (-C≡C-Py) to form a rigid and highly symmetrical 109.5° building block in which the fluorophore subunit is vertically aligned to the plane formed by the -C≡C-Py donors. Upon reaction of the above tecton with a 90° organoplatinum acceptor unit, an intensely fluorescent rhomboid cavitand was manifested in solution. In contrast to the vast majority of coordination-driven self-assembled chromophoric systems, the present one fully conserves the excellent photophysical properties of the parent Bodipy dye. These unique features of the present metallosupramolecular entity constitute a fascinating metal-to-ligand self-assembled prototype for building compact and intensely luminescent materials with host-guest capabilities.
We herein present the coordination-driven supramolecular synthesis and photophysics of a [4+4] and a [2+2] assembly, built up by alternately collocated donor-acceptor chromophoric building blocks based, respectively, on the boron dipyrromethane (Bodipy) and perylene bisimide dye (PBI). In these multichromophoric scaffolds, the intensely absorbing/emitting dipoles of the Bodipy subunit are, by construction, cyclically arranged at the corners and aligned perpendicular to the plane formed by the closed polygonal chain comprising the PBI units. Steady-state and fs time-resolved spectroscopy reveal the presence of efficient energy transfer from the vertices (Bodipys) to the edges (PBIs) of the polygons. Fast excitation energy hopping - leading to a rapid excited state equilibrium among the low energy perylene-bisimide chromophores - is revealed by fluorescence anisotropy decays. The dynamics of electronic excitation energy hopping between the PBI subunits was approximated on the basis of a theoretical model within the framework of Förster energy transfer theory. All energy-transfer processes are quantitatively describable with Förster theory. The influence of structural deformations and orientational fluctuations of the dipoles in certain kinetic schemes is discussed.
We herein present the supramolecular construction of a completely fluorescent unquenched multichromophoric wheel consisting of boron dipyrromethene dyes arranged perpendicularly to the circular plane.
We present here the self-assembly of a green-emitting metallosupramolecular rhomboid into a rigid, highly-ordered 3D multichromophoric network through the mediation of a tetra-anionic violet-blue molecular emitter. Control was obtained on the spatial topology, the electronic energy landscape and the fluorescence polarization of the interacting dipoles.
The geometric isomeric diversity of a centrosymmetrically disubstituted naphthalene derivative with flexible methoxytriethyleneglycol chains has been investigated both in the liquid and the solid state. Owing to the fact that the exocyclic C(Aryl)-O linking appears to be essentially a double bond, the material can exist in discrete geometric isomers. Variable temperature ultraviolet absorption and fluorescence spectroscopy combined with single crystal X-ray diffraction reveal the nature of the various stereoisomers present in the liquid and solid phase. Computational support is also given wherever possible. In solution, the material exists predominantly as a mixture of two rapidly interconverting stereoisomers; namely, the thermodynamically preferred cis, cis and the energetically closest lying cis, trans configuration. In the solid state, optical spectroscopic methods provide evidence for the presence of a small amount of the energetically highly unstable trans, trans stereoisomer, kinetically trapped in the lattice defined by the scaffold of the predominant cis, cis isomeric form. Unlocking of the seemingly frozen cis, cis right arrow over left arrow trans, trans equilibrium was observed in the molten state.
We present herein a host-guest supramolecular system by which we were able to obtain precise control of the stereospecificity of a new and unusual adiabatic photoisomerization reaction capable of restoring reversibly the original configuration. The host-guest system is composed of (a) a naphthalene ring linked centrosymmetrically-via sp(2) hybridized oxygen atoms-with methoxytriethyleneglycol chains (1) and (b) a nanotubular cage formed by four self-assembled face-to-face β-cyclodextrins threaded onto the long "axle" of 1. The compound 1 can exist in distinct cis,cis, cis,trans, and trans,trans conformations that are spectrally distinguishable (see Scheme 1 ). Spectroscopic and kinetic manifestations of the torsional isomerization of 1 in the lowest excited singlet state both in solution and within the tubular cage were investigated. The results provide clear evidence that the compact cavity completely blocks the photoisomerization pathway manifested in common solution (cis,cis* → cis,trans*), allowing observation of stereospecific, volume-conserving turning of the naphthalene ring about the two "quasidouble" bonds C(Naph)-O by φ ≈ 180° (cis,cis* → trans,trans*). The photoisomerization is purely adiabatic, and the encaged molecule restores its original configuration by generating torque thermally, when relaxing to the ground state.
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