Atomically resolved TEM imaging of covalently functionalised graphene

Covalent functionalisation can be a powerful lever to tune the properties and processability of graphene. After overcoming the low chemical reactivity of graphene, covalent functionalisation led to the generation of new hybrid materials, applicable in a broad variation of fields. Although the process of functionalising graphene is nowadays firmly established, fundamental aspects of the produced hybrid materials remain to be clarified. Especially the atomically resolved imaging is only scarcely explored. Here we show aberration corrected in situ high resolution TEM imaging of dodecyl functionalised monolayer graphene at atomic resolution after an effective mechanical filtering approach. The mechanical filtering allows to separate adsorbed contamination from the covalently bound functional molecules and thus opens the possibility for the observation of this hybrid material. The obtained data is validated by DFT calculations and by a novel image simulation approach based on molecular dynamics (MD) simulations at room temperature

Highly strained, radially π-conjugated porphyrinylene nanohoops

Small π-conjugated nanohoops are difficult to prepare, but offer an excellent platform for studying the interplay between strain and optoelectronic properties, and, increasingly, these shape-persistent macrocycles find uses in host-guest chemistry and self-assembly. We report the synthesis of a new family of radially π-conjugated porphyrinylene/phenylene nanohoops. The strain energy in the smallest nanohoop [2]CPT is approximately 54 kcal mol⁻¹, which results in a narrowed HOMO-LUMO gap and a red shift in the visible part of the absorption spectrum. Because of its high degree of preorganization and a diameter of ca. 13 Å, [2]CPT was found to accommodate C₆₀ with a binding affinity exceeding 10⁸ M⁻¹ despite the fullerene not fully entering the cavity of the host (X-ray crystallography). Moreover, the ?-extended nanohoops [2]CPTN, [3]CPTN, and [3]CPTA (N for 1,4-naphthyl; A for 9,10-anthracenyl) have been prepared using the same strategy, and [2]CPTN has been shown to bind C₇₀ 5 times more strongly than [2]CPT. Our failed synthesis of [2]CPTA highlights a limitation of the experimental approach most commonly used to prepare strained nanohoops, because in this particular case the sum of aromatization energies no longer outweighs the buildup of ring strain in the final reaction step (DFT calculations). These results indicate that forcing ring strain onto organic semiconductors is a viable strategy to fundamentally influence both optoelectronic and supramolecular properties

Dynamic Covalent Formation of Concave Disulfide Macrocycles Mechanically Interlocked with Single-Walled Carbon Nanotubes

The formation of discrete macrocycles wrapped around single-walled carbon nanotubes (SWCNTs) has recently emerged as an appealing strategy to functionalize these carbon nanomaterials and modify their properties. Here, we demonstrate that the reversible disulfide exchange reaction, which proceeds under mild conditions, can install relatively large amounts of mechanically interlocked disulfide macrocycles on the one-dimensional nanotubes. Size-selective functionalization of a mixture of SWCNTs of different diameters were observed, presumably arising from error correction and the presence of relatively rigid, curved π-systems in the key building blocks. A combination of UV/Vis/NIR, Raman, photoluminescence excitation, and transient absorption spectroscopy indicated that the small (6,4)-SWCNTs were predominantly functionalized by the small macrocycles 12 , whereas the larger (6,5)-SWCNTs were an ideal match for the larger macrocycles 22 . This size selectivity, which was rationalized computationally, could prove useful for the purification of nanotube mixtures, since the disulfide macrocycles can be removed quantitatively under mild reductive conditions

Highly Strained, Radially π-Conjugated Porphyrinylene Nanohoops

Small π conjugated nanohoops are difficult to prepare, but offer an excellent platform for studying the interplay between strain and optoelectronic properties and increasingly, these shape persistent macrocycles find uses in host guest chemistry and self assembly. We report the synthesis of a new family of radially π conjugated porphyrinylene/phenylene nanohoops. The strain energy in the smallest nanohoop [2]CPT is approx-imately 54 kcal mol-1, which results in a narrowed HOMO LUMO gap and a red shift in the visible part of the absorption spectrum. Due to its high degree of preorganization and a diameter of ca. 13 Å, [2]CPT was found to accommodate C60 with a binding affinity exceeding 108 M-1 despite the fullerene not fully entering the cavity of the host (X Ray crystallography). Moreover, the π extended nanohoops [2]CPTN , [3]CPTN and [3]CPTA (N for 1,4 naphthyl; A for 9,10 anthracenyl) have been prepared using the same strategy, and [2]CPTN has been shown to bind C70 five times more strongly than [2]CPT. Our failed synthesis of [2]CPTA highlights a limitation of the experimental approach most commonly used to prepare strained nanohoops, because in this particular case the sum of aromatization energies no longer outweighs the buildup of ring strain in the final reaction step (DFT calculations). These results indicate that forcing ring strain onto organic semiconductors is a viable strategy to fundamentally influence both optoelectronic and supramolecular properties.</p

Highly strained, radially π-conjugated porphyrinylene nanohoops

Small π-conjugated nanohoops are difficult to prepare, but offer an excellent platform for studying the interplay between strain and optoelectronic properties, and, increasingly, these shape-persistent macrocycles find uses in host-guest chemistry and self-assembly. We report the synthesis of a new family of radially π-conjugated porphyrinylene/phenylene nanohoops. The strain energy in the smallest nanohoop [2]CPT is approximately 54 kcal mol⁻¹, which results in a narrowed HOMO-LUMO gap and a red shift in the visible part of the absorption spectrum. Because of its high degree of preorganization and a diameter of ca. 13 Å, [2]CPT was found to accommodate C₆₀ with a binding affinity exceeding 10⁸ M⁻¹ despite the fullerene not fully entering the cavity of the host (X-ray crystallography). Moreover, the ?-extended nanohoops [2]CPTN, [3]CPTN, and [3]CPTA (N for 1,4-naphthyl; A for 9,10-anthracenyl) have been prepared using the same strategy, and [2]CPTN has been shown to bind C₇₀ 5 times more strongly than [2]CPT. Our failed synthesis of [2]CPTA highlights a limitation of the experimental approach most commonly used to prepare strained nanohoops, because in this particular case the sum of aromatization energies no longer outweighs the buildup of ring strain in the final reaction step (DFT calculations). These results indicate that forcing ring strain onto organic semiconductors is a viable strategy to fundamentally influence both optoelectronic and supramolecular properties

A model hamiltonian tuned toward high level ab initio calculations to describe the character of excitonic states in perylenebisimide aggregates

On the example of an aggregate of two perylenebisimide (PBI) molecules the character of the lowest excited electronic states in terms of charge transfer (CT) and Frenkel exciton (FE) configurations is investigated as a function of the intermolecular arrangement. A minimal model Hamiltonian based on two FE and two CT configurations at the frontier-orbitals CIS (FOCIS) level is shown to represent a simple and comprehensible approach providing insight into the physical significance of the model Hamiltonian matrix elements. The recently introduced analysis and diabatization procedure (Liu et al., J. Chem. Phys. 2015, 143, 084106) method is used to extract the energies of the configurations and their interactions (the model Hamiltonian parameters) also from the accurate CC2 approach. An analysis in terms of diabatic energy profiles and their interactions shows that the FOCIS parameters give a qualitatively correct description of the adiabatic excited state energy profiles. Comparison with CC2 reveals, however, the presence of avoided crossings at FOCIS level, associated with a large character change (CT/FE) of the excited states as a function of the aggregate structure, which represents the major drawback of FOCIS results. We show that proper amendment of the FOCIS-derived parameters allows to accurately represent the potential energy surfaces and crossings of the excited dimer states as a function of the aggregate structure. \ua9 2018 Wiley Periodicals, Inc