Polyphenylene dendrimers with perylene diimide as a luminescent core

Modulating the Photophysical Properties and Electron Transfer Rates in Diketopyrrolopyrrole-Based Coordination Polymers

Molecular self-assembly through noncovalent interactions is a particularly efficient approach to fine-tune the optoelectronic and photophysical properties of electroactive materials. In metal-ligand coordination polymers, the final properties of the assemblies are directly related to the nature of the metal-ligand interaction. To probe for such influence on the photophysical properties of electroactive materials, a series of coordination polymers based on a well-known organic dye, diketopyrrolopyrrole, was prepared through coordination of a terpyridine-containing monomer with various metal sources, including iron, cobalt, zinc, and manganese. The resulting supramolecular polymers were characterized through multiple techniques, including UV-vis and fluorescence spectroscopy, time-correlated single-photon counting, and femtosecond transient absorption spectroscopy to reveal the impact of the metal source on the final photophysical properties of coordination polymers. As expected, important variations were found between different coordination polymers in terms of absorption, fluorescence kinetics, and electron transfer rate. While iron and cobalt-containing polymers showed ultrafast electrons transfer rates, assemblies from manganese were shown to be much less efficient, confirming the importance of metal centers. This detailed fundamental study unravels some important relationships between metal-ligand interactions, supramolecular self-assembly, and photophysical properties, ultimately leading to new avenues for the design of functional polymers based on organic dyes.

Synthesis of diverse heterocyclic frameworks using cyclopentadienones via the Diels–Alder strategy

In this review article, we briefly summarize the versatility of Diels–Alder reactions of cyclopentadienones and concise routes to diverse hetero-atom bearing PAHs using cyclones as building blocks.

Alkyloxy modified pyrene fluorophores with tunable photophysical and crystalline properties

Alkyloxy modified 4,5,9,10-tetrasubstituted pyrenes display tunable photophysical and crystalline properties depending on the alkyl chains attached at the polyaromatic core.

Single-Molecule Break Junctions Based on a Perylene-Diimide Cyano-Functionalized (PDI8-CN2) Derivative

In this letter, we report the single-molecule conductance properties of a cyano-functionalized perylene-diimide derivative (PDI8-CN2) investigated with gold nano-electrodes. This molecule is of large interest for the fabrication of high-performance and air-stable n-type organic field-effect transistors. Low-bias experiments performed on mechanically controllable break junctions reveal the presence of two different values of the single-molecule conductance, which differ by about two orders of magnitudes. Up to date, this feature was never observed for other perylene-diimide compounds having alternative chemical moieties attached to the basic aromatic core. Theoretical calculations suggest that the highest single-molecule conductance value here observed, comprised between 10(-2) and 10(-3) G0, is related to a charge transport path directly linking the two cyano groups.

The polar side of polyphenylene dendrimers

The site-specific functionalization of poly(phenylene) dendrimers can produce macromolecules with a range of different polarities.

Probing the dendritic architecture through AIE: challenges and successes

Since the aggregation-induced emission (AIE) phenomenon is very sensitive to steric hindrance, we set out to use it as a tool to probe the periphery of dendrimers.

Fluorescence enhancement from individual plasmonic gap resonances

We studied the fluorescence enhancement of a dye-loaded polyphenylene dendrimer in a gap of 2-3 nm between a silver film and single silver particles with an average diameter of 80 nm. This sphere-on-plane geometry provides a controllable plasmonic resonator with a defined dye position. A strong fluorescence signal was seen from all particles, which was at least 1000 times stronger than the signal from the plane dye-coated metal surface. The fluorescence emission profile varied between the particles and showed light emission at higher energies than the free dye, which we assigned to hot luminescence. The maximum fluorescence emission peak shifted along with the scattering maximum of the plasmonic resonance. Two classes of scattering resonators could be distinguished. Up to a significant line-broadening, the response of the "sphere-on-plane"-like cases resembled the theoretical prediction for a perfect sphere-on-plane geometry. Resonators which deviate strongly from this ideal scenario were also found. Electron microscopy did not show significant differences between these two classes, suggesting that the variations in the optical response are due to nanoscale variations of shape and roughness in the gap region. The strong modifications of the dye emission spectrum suggested the presence of physical mechanisms at very small metal/dye separations, which are beyond a simple wavelength-dependent enhancement factor.

Metallocene-containing conjugated polymers

The paper gives a review of publications on polymers with conjugated matrices (PPy, PTh, PAni, hydrocarbon or mixed chains...) which incorporate metallocene complexes (Fe, Ru, Co; Ni, Ti, Zr, Ta) with two cyclopentadienyl ligands (Cp) and their derivatives, in particular with methylated cyclopentadienyl rings (Cp*), as well as hemi-metallocene complexes (Fe, Ru, Co, Mn), as pendant groups or inside the principal chain (part B). The information on related short-chain systems, monomers and oligomers, is also included. In part A, a brief overview of various conjugated polymer materials is presented, with their classification in accordance with the conductivity mechanism (ionic, electronic or mixed conductors) or with the structural type (linear-chain organic or mixed polymers, derivatization, metallopolymers, multi-dimensional structures, alternating and block copolymers with organic or mixed units, hybrid materials with a mixture of conjugated and inert polymers, polymers inside a solid matrix, conjugated polymers with incorporated nanoelements of transition metals, carbon, semiconductors etc.

Molecular modeling simulations of the morphology of polyphenylene dendrimers

Three polyphenylene dendrimers were studied by molecular modeling techniques with the goal of better defining the notion of shape persistence often associated with these molecules. We show that despite the rigidity of the monomers, a large variety of dendrimer morphologies is accessible, in large part due to the asymmetrical branching pattern of the monomers (they have nodes in meta and para positions with respect to their anchor point). The folding ability of a branch depends on the number and sequence of the meta and para nodes it contains: while some of the branches are always straight, others can fold back, and the amplitude of that folding increases with generation. As a result, the range of accessible morphologies increases with the generation, from a dense-shell model in low generation to a model intermediate between a dense shell and a dense core in high generation. When the typical A2B monomer is replaced by an A4B monomer, the dense packing limit is reached as early as the second generation because of a higher density and the presence of nodes in the ortho position, which are oriented backward.

Light harvesting and efficient energy transfer in a boron-dipyrrin (BODIPY) functionalized perylenediimide derivative

[reaction: see text] Click chemistry has been successfully applied in the synthesis of a bay region tetraboron-dipyrrin (BODIPY) appended perylenediimide (PDI). This light-harvesting molecule presents a large cross section for the absorption of light in the visible region. Excitation energy is efficiently channeled to the perylenediimide core. This novel antenna system is the first demonstration of the efficiency of energy transfer in a BODIPY-PDI bichromophoric system and appears to be highly promising for the design and synthesis of similar dendritic structures.

Multichromophoric Polyphenylene Dendrimers: Toward Brilliant Light Emitters with an Increased Number of Fluorophores

Two routes for the introduction of highly fluorescent peryleneimide chromophores into the scaffolding of polyphenylene dendrimers via iterative Diels-Alder cycloadditions are presented. The key intermediates for the divergent dendrimer buildup were two cyclopentadienone branching units carrying two peryleneimides and two masked terminal alkynes. The difference between the two reagents is the mode of incorporation of the chromophores. In the first case, the chromophores were attached to the alpha-position of the tetraphenylcyclopentadienones. In the second case, peryleneimides are used as a "spacer" in the beta-position of the cyclopentadienones giving rise to dendrimers with extended molecular diameters (up to 12 nm) and 24 chromophores within their scaffold. Absorption and emission characteristics of the new multichromophoric nanoparticles were investigated and compared to those of the parent dyes. Additionally, an asymmetrically substituted first-generation dendrimer with six perylene diimide chromophores and one ester functionality is reported. The ester serves as a potential anchor group, and this nanoemitter paves the way to a multichromophoric fluorescence label. All dendrimers have good solubility in common organic solvents, high fluorescence quantum yields, and defined distances between the chromophores, making them attractive candidates for single-molecule spectroscopy.

Phosphorus(V) Porphyrins with Axial Carbazole-Based Dendritic Substituents

[structure: see text] Three phosphorus(V) porphyrins with axial carbazole-based dendritic substituents (D-A-D) have been designed and synthesized, which are nonfluorescent due to their effective electron transfer from the carbazole dendron to the excited porphyrin within the dendritic matrix. The incident photon to current conversion efficiencies (IPCE) spectra demonstrate that the molecular structure of the dendrimers can significantly affect the photovoltaic response to the visible light.

Pyrene as chromophore and electrophore: encapsulation in a rigid polyphenylene shell

Starting from the fourfold ethynyl-substituted chromophore 1,3,6,8-tetraethynylpyrene as core, a series of polyphenylene dendrimers was prepared in high yield by combining divergent and convergent growth methods. The fluorescence quantum yields (Q(f)>0.92) of the encapsulated pyrene chromophore were independent of the size of the polyphenylene shell. Fluorescence quenching studies and temperature-dependent fluorescence spectroscopy were performed to investigate the site isolation of the core. They indicate that a second-generation dendrimer layer is needed to efficiently shield the encapsulated pyrene and prevent aggregate formation. Alkali-metal reduction of the encapsulated pyrene core was carried out to afford the corresponding pyrene radical anions, for which hampered electron transfer to the core was observed with increasing dendrimer generation, which is further proof of the site isolation due to the polyphenylene shell. To improve film formation and solubility of the material, solubilizing alkyl chains were introduced on the periphery of the spherical particles. Furthermore, highly transparent films obtained by a simple drop-casting method showed blue emission mainly from the unaggregated species. The materials presented herein combine high quantum efficiency, good solubility, and improved film-forming properties, which make them possible candidates for several applications in electronic devices.

Non-conjugated, phenyl assisted coupling in through bond electron transfer in a perylenemonoimide–triphenylamine system

Two donor-bridge-acceptor compounds containing triphenylamine (TPA) donors and perylenemonoimide (PMI) acceptors have been studied by spectroscopic techniques and quantum chemical computation. Both systems have been observed to emit prompt and delayed fluorescence under certain conditions indicating that forward and reverse electron transfer (ET) processes can occur between the locally excited and the charge separated states. The experimental and computational results show that the TPA and PMI chromophores are better coupled by almost 50% in the meta isomers which undergo ET more readily than the para isomers. Quantum chemical calculations indicate that this unexpected situation is the result of a phenyl group on the side of the bridge being advantageously positioned in the meta isomers. This leads to more extensive delocalisation of the TPA HOMO into the bridge enhancing the total through bond electronic coupling between the TPA and PMI chromophores. The calculations also indicate a strong angle dependence of the total coupling in both isomers. The experimental results are discussed in the context of the high temperature limit of Marcus's theory of non-adiabatic ET.