Optimal Synergy between Azulenes and Acenes in Azuacenes with 6‑7‑5 Ring Topology

Abstract

Azuacenes, defined as azulene fused with acenes in a 6-7-5 ring topology and spanning lengths from 3 to 6 rings, have been synthesized using a new skeleton editing and [3 + 2] annulation synthesis protocol as a distinction regarding the procedures to obtain the 6-5-7 isomers. Comprehensive studies on ground-state and excited-state spectroscopy, electrochemical properties, chemical stability, and solid-state structure have been conducted to compare these azuacenes with acenes. For the same number of rings, we found that azuacenes improve the chemical stability of acenes (i.e., smaller diradical character) and their photophysical properties (i.e., anti-Kasha emissions and modulation of the energy and strength of the visible bands) but they reduce the transport features compared to those of acenes. Compared with azulene, azuacenes improve the performance of azulene in terms of electrical properties. Overall, the fusion of known polycyclic compounds, such as acene and azulene, produces new isomeric hybrid compounds with enhanced properties. Here, the resulting compounds turn out to conserve most of the unique properties of the two building blocks that we associate with the facility of π-delocalization of the positive charge of the azulene zwitterion over the acene fragment.