Synthesis, Characterization, and Properties of [4]Cyclo‐2,7‐pyrenylene: Effects of Cyclic Structure on the Electronic Properties of Pyrene Oligomers

Abstract

A cyclic tetramer of pyrene, [4]cyclo-2,7-pyrenylene ([4]CPY), was synthesized from pyrene in six steps and 18 % overall yield by the platinum-mediated assembly of pyrene units and subsequent reductive elimination of platinum. The structures of the two key intermediates were unambiguously determined by X-ray crystallographic analysis. DFT calculations showed that the topology of the frontier orbitals in [4]CPY was essentially the same as those in [8]cycloparaphenylene ([8]CPP), and that all the pyrene units were fully conjugated. The electrochemical analyses proved the electronic properties of [4]CPY to be similar to those of [8]CPP. The results are in sharp contrast to those obtained for the corresponding linear oligomers of pyrene in which each pyrene unit was electronically isolated. The results clearly show a novel effect of the cyclic structure on cyclic pconjugated molecules.

Theoretical Study of Cyclic Pyrene Oligomers and Their Resemblance with Cyclic Paraphenylenes: Disclosing Structure–Property Relationships for Cyclic Nanorings

“…This fact might be related with a less favored synthesis due to higher structural and/or steric difficulties. Note that the strain energy of [4]CPY calculated before, 21 at the B3LYP/6-31G* level and thus without considering non-covalent interactions, is close to the value obtained in this work, although not completely similar due to the introduction here of intra-molecular non-covalent interactions.…”

“…a Values taken from reference [21] b Values taken from reference [37] Figure 3 shows the energy and shape of the fully delocalized HOMO and LUMO orbitals for the [n]CPY systems and the pyrene monomer. Similarly to strain energies, when the size of the system increases, the HOMO energy decreases, while the LUMO energy increases, which produces, obviously, a larger HOMO-LUMO energy difference with the system size (see also To conclude the part of the study dealing with the properties of isolated nanorings, the UV-Vis absorption spectra has also been computed at the TD-PBE0/cc-pVDZ level using the Polarizable Continuum Model (PCM), with the default technical parameters and using chloroform as solvent, at the previously solvated (in chloroform) reoptimized structures at the B3LYP-D3(BJ)/cc-pVDZ level.…”

“…Table 3 been extracted from its crystalline form, and used rigidly herein. Due to the fact that dihydro [4]CPY is the only compound with a fully resolved crystal structure, 21 we have consequently removed the solvent molecules (occluded into the cavity of the nanoring) and unsaturated correspondingly the molecule. The intermolecular interaction energy of every extracted dimer, ΔEint, depends on the geometrical arrangements of the isolated monomers to form the dimers at the crystal structure, and it has been calculated by subtracting the energy of both monomers at the dimer geometry (G crystal ) from that of the dimer 38…”

“…Furthermore, despite of some similarity between pyrene and biphenyl rings, their structural and electronic structure are completely different, motivating us to study the effect of inserting pyrene units inside these cyclic organic structures. 21 In this sense, the comparison between CPY and CPP analogues could be useful to understand their behavior as precursors for the bottom-up synthesis of structurally uniform armchair CNTs, or for some other envisioned applications of these promising CNT segments. 22 Herein, we have studied from a theoretical point of view a series of CPYs (ranging between [3] to [5]CPYs) in order to determine: (i) how the structural, electronic, and energetical properties of isolated [3][4][5]CPY systems theoretically evolve with system size; and (ii) how these systems self-assemble in the solid-state, chosen [4]CPY (the only system synthesized so far) as a case study, after calculating the non-covalent interactions between the set of unique molecular arrangements found in crystalline samples.…”

Synthesis of [n]Cyclo‐5,15‐porphyrinylene‐4,4′‐biphenylenes Displaying Size‐Dependent Excitation‐Energy Hopping

“…[4] Later,t his synthetic method was extended to include the Vernier template strategy,w hich has enabled the synthesis of specific large porphyrin wheels from linear oligomers through the use of as uitable templating host molecule,t hus highlighting its effectiveness in overcoming the entropic disadvantages and inherent structural strain associated with cyclization. This strategy was initially employed to synthesize cyclic 2,5-oligothiophenes and [n]cycloparaphenylenes ([n]CPP), [5][6][7] and has been used for the synthesis of nickel(II) [n]cyclo-2,12-porphyrinylenes [n]CP from 2,12-diborylated Ni II porphyrins (Scheme 1b). This strategy was initially employed to synthesize cyclic 2,5-oligothiophenes and [n]cycloparaphenylenes ([n]CPP), [5][6][7] and has been used for the synthesis of nickel(II) [n]cyclo-2,12-porphyrinylenes [n]CP from 2,12-diborylated Ni II porphyrins (Scheme 1b).…”