A Pentacene‐based Nanotube Displaying Enriched Electrochemical and Photochemical Activities

Abstract

Unlike previously well‐studied, acyclic pentacene oligomers, the first synthesis of a cyclic pentacene trimer with a fixed tubular conformation is reported. A short‐step synthesis starting from common pentacenequinone yielded the target molecule with a 1.5 nanometer length and a subnanometer pore. Steady‐state spectroscopic analyses revealed that the close proximity of the non‐conjugated, three pentacene chromophores allows the nanotube to display stepwise electrochemical/chemical oxidation characteristics. Furthermore, time‐resolved transient absorption measurements elucidated the generation of an excited triplet state of the nanotube, with high quantum yield reaching about 180 % through intramolecular singlet fission and a very long triplet lifetime.

A Free‐Radical Prompted Barrierless Gas‐Phase Synthesis of Pentacene

“…This interest is based on their exceptional optoelectronic properties-often in combination with Buckminster-fullerene (C 60 )-as organic semiconductors [3] and organic field effect transistors (OFETs). [4] Acenes also play a fundamental role as molecular building blocks in nanotubes, [5] graphenes, [6] nanoflakes, [7] and fullerenes (C 70 ) (Scheme 2) [8] and have been suggested as potential carriers of (some of) the diffuse interstellar bands (DIBs) [9] -discrete absorption features overlaid on the interstellar extinction curve from the blue part of the visible (400 nm) to the nearinfrared (1.2 mm). [10] Structurally, the 22 p-aromatic pentacene (C 22 H 14 ) represents a linear (planar) acene with tetracene (C 18 H 12 ) and hexacene (C 26 H 16 ) defining the previous and next member in the homologous series, respectively.…”

Closed Aromatic Tubes—Capsularenes

“…The formation of such rigid and tubular nanostructures [16] from flexible molecular baskets is a quantitative process driven by desolvation in which TFA acts as encapsulation catalyst. [55] While optical and redox characteristics of acenes are, within capsularenes, somewhat perturbed, [19] their thermal stability is significantly improved. [15] Moreover, the unique mode of packing of capsularenes in solid-state, dominated by CÀ H-π and π-π intermolecular contacts, arises from their tubular shape and rigidity.…”

“…the band gap) and engineering their assembly in the solid state is essential for obtaining materials with desired properties (conductivity, emission characteristics, stability, etc.). Fascinatingly, macrocyclic dimers [17] and trimers [18] (Figure 1C) [19] of acenes have shown emerging electronic characteristics [20] with smaller band gaps, [17a] RGB luminescence [21] and the unique ability to undergo singlet fission [19] -a process in which an excited singlet state breaks into two triplets. [22] It follows that capsularenes having acene chromophores within a rigid tube-shaped scaffold (Figure 1B), could give rise to robust organic electronic materials with excellent chemical and thermal stability as well as long-range order in the solid state.…”

Closed Aromatic Tubes—Capsularenes

“…Chemie nanostructures [16] from flexible molecular baskets is a quantitative process driven by desolvation in which TFA acts as encapsulation catalyst. [55] While optical and redox characteristics of acenes are, within capsularenes, somewhat perturbed, [19] their thermal stability is significantly improved. [15] Moreover, the unique mode of packing of capsularenes in solid-state, dominated by CÀ H-π and π-π intermolecular contacts, arises from their tubular shape and rigidity.…”