The photophysical properties of two pyrene-bodipy molecular dyads, composed of a phenyl-pyrene (Py-Ph) linked to the meso position of a bodipy (BD) molecule with either H-atoms (BD1) or ethyl groups (BD2) at the 2,6 positions, are investigated by stationary, nanosecond and femtosecond spectroscopy. The properties of these dyads (Py-Ph-BD1 and Py-Ph-BD2) are compared to those of their constituent chromophores in two solvents namely 1,2-dichloroethane (DCE) and acetonitrile (ACN). Stationary spectroscopy reveals a weak coupling among the subunits in both dyads. Excitation of the pyrene (Py) subunit leads to emission that is totally governed by the BD subunits in both dyads pointing to excitation energy transfer (EET) from the Py to BD chromophore. Femtosecond fluorescence and transient absorption spectroscopy reveal that EET takes place within 0.3-0.5 ps and is mostly independent of the solvent and the type of the BD subunit. The EET lifetime is in reasonable agreement with that predicted by Förster theory. After EET has taken place, Py-Ph-BD1 in DCE and Py-Ph-BD2 in both solvents decay mainly radiatively to the ground state with 3.5-5.0 ns lifetimes which are similar to those of the individual BD chromophores. However, the excited state of Py-Ph-BD1 in ACN is quenched having a lifetime of 1 ns. This points to the opening of an additional non-radiative channel of the excited state of Py-Ph-BD1 in this solvent, most probably charge separation (CS). Target analysis of the TA spectra has shown that the CS follows inverted kinetics and is substantially slower than the recombination of the charge-separated state. Occurrence of CS with Py-Ph-BD1 in ACN is also supported by energetic considerations. The above results indicate that only a small change in the structure of the BD units incorporated in the dyads significantly affects the excited state dynamics leading either to a dyad with long lifetime and high fluorescence quantum yield or to a dyad with ability to undergo CS.

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 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 intramolecular excitation energy transfer (EET) processes in a series of fluorescent-unquenched, self-assembled metallocycles consisting of spatially fixed-separated and parallel-aligned Bodipy chromophores, are investigated here by steady-state and femtosecond-fluorescence upconversion measurements in the solution phase. These multi-Bodipy macrocycles, namely, the rhomboid (A1), the tetragon (A2) and the hexagon (A3), are formed via temperature-regulated Pt­(II)–pyridyl coordination and consist, respectively, of two, four, and six Bodipy subunits, which are locked at the corners and aligned with their long molecular axes perpendicular to the rigid polygonal frame formed by the alternating B···Pt­(II) connectivities. Extensive simulations and fits to the experimental fluorescence anisotropy decays r(t) show that EET within the cyclic scaffolds is quite uniform and much faster than the intrinsic decay rate of the Bodipy’s. The equalization of the excitation survival probabilities over time of all chromophores is found to be dependent upon the size of the macrocycle. From the observed dynamics supported by geometry optimization calculations, it is concluded that, in contrast to the model compound A1, in the large macrocycles the perfect parallel orientation of the Bodipy dipoles is lifted through limited out-of-plane distortions of the metallocyclic framework from a planar conformation. Additionally, we show that, as opposed to analogous covalent macrocycles, the survival probability of excitons as well as the degree of symmetry distortion and homogeneity in dipole spacing remains nearly intact as the size of the macrocycle increases from tetragon to hexagon.

Identifying the role of multiple cooperative supramolecular interactions and the working mechanism underlying the formation of sophisticated, well-defined self-assembled architectures is definitely a challenging and formidable task in understanding the complexity in chemical systems and engineering the properties of advanced materials. The topological design of multifunctional tectons, capable of self-organizing into patterned supramolecular assemblies comprising stacked aromatic molecules, is of particular importance because it can lead to the predictable emergence of controlled functions with tailored electronic properties. Herein, we provide spectroscopic, structural, and mechanistic insights on metal-ion-mediated self-assembly of a charged, amphiphilic perylene-bisimide (PBI) dimer S into two-dimensional (2D) arrays consisting of parallel columnar PBI stacks with a precise spatial arrangement and pattern behavior, using a readily accessible design strategy. The building block (S), a centrosymmetric PBI homodimer bearing a disulfonated trans-stilbene core, was designed to concurrently feature high complexation directionality with a strong binding affinity through multiple supramolecular interactions. In solvents that efficiently solvate PBI, e.g., chloroform, the zinc ion interacts strongly through electrostatic interactions with the negatively charged core of S, and with the π cloud of the stilbene moiety (cation−π interactions) forming simple 1:1 adducts. In methanol, the findings manifest the efficient formation of well-defined aggregates with H-type excitonic coupling. A single-crystal X-ray structure reveals, despite the sterically crowded bay area of PBIs constituting S, an unprecedented pattern of 2D arrays comprising face-to-face, slipped π-stacked PBI interdimers that pack in parallel columns. This molecular arrangement explains the quenched fluorescence in solution, as well as the appearance of weak excimer-like fluorescence both in solution and crystals. The spectroscopic and structural findings converge to the conclusion that the development of aggregates in solution proceeds by a cooperative growth process driven by a collection of different supramolecular interactions, i.e., electrostatic (core of S), π–π stacking (terminal PBIs), and multiple C–H···π (bay substituents). A corresponding aggregation model fits satisfactorily the experimental data in solution and allows extracting the association constants and spectra of the equilibrated species.