Inducing Curvature to Pyracylene upon π‐Expansion

Abstract

We disclose a successive π‐expansion of pyracylene towards boat‐shaped polycyclic scaffolds. The unique structural features of the resulting compounds were revealed by X‐ray crystallographic analysis. Depending on the extent of π‐expansion the compounds display intense bathochromically shifted absorption bands in their UV/Vis spectra and are prone to several redox events as documented by cyclic voltammetry. The experimental observations are in line with the computational studies based on density functional theory, suggesting progressive narrowing of the HOMO–LUMO gap and distinct evolution of the electronic structure and aromaticity.

A Negatively Curved π‐Expanded Pyracylene Comprising a Tropylium Cation

“…The structural features of SPH , MesPH , and MesPH + BF 4 − were elucidated by X‐ray crystallographic analysis [16] . In the solid state, all compounds feature a distinct boat‐shaped geometry, which has also been observed previously for the π‐expanded pyracylene [13] . The introduction of the 7‐membered ring leads to a pronounced negative curvature in the direct periphery of the respective wing.…”

“…derivatives. [10,11,13] The gradual expansion of the π-scaffold upon successive cyclization is mirrored in a progressive redshift of the lowest energy absorption maxima of the compounds. Whereas uncyclized HSP features a lowest energy absorption maximum at 451 nm, the partially cyclized congeners DSP and TSP show similar absorption properties with maxima at 545 and 539 nm, respectively.…”

A Negatively Curved π‐Expanded Pyracylene Comprising a Tropylium Cation

“…[16] In the solid state, all compounds feature a distinct boatshaped geometry, which has also been observed previously for the π-expanded pyracylene. [13] The introduction of the 7membered ring leads to a pronounced negative curvature in the direct periphery of the respective wing. In contrast, the other wing comprising exclusively 6-membered rings remains almost planar (Figure 2A).…”

“…[9][10][11][12] Recently, our group published a boat-shaped hexa-perihexabenzocoronene-pyracylene hybrid (HPH) with multistage redox properties. [13] Motivated by these findings we envisioned that incorporation of a π-conjugated 7-membered ring into the polycyclic scaffold might allow unique modulation of its electronic properties and induction of negative curvature. Specifically using a tropone unit shall provide for efficient tuning by chemical manipulation of the carbonyl group towards the respective tropylium cation (Figure 1).…”

N‐Doped Nonalternant Nanoribbons with Excellent Nonlinear Optical Performance

“…The synthetic route to NNNR‐1 and NNNR‐2 is shown in Scheme 1. According to the reported method, three key compounds (1, [22] 2, [23] and 5 [24] ) were readily prepared. Firstly, Pd‐catalyzed coupling reaction between compounds 1 and 2 in the presence of Pd 2 (dba) 3 /( t ‐Bu) 3 P ⋅ HBF 4 and excess 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) was conducted at 145 °C, affording the intermediate 3 in 28 % yield.…”