Efficient Synthesis of Azulene-Fused Acenes: Aromaticity Evolution, Anti-Kasha Emission, and Hole Transport

The intrinsic instability of larger acenes remains a central obstacle to their application in organic electronics. Here we report an annulative synthetic strategy enabling the in situ construction of azulene units and their fusion into acene backbones, providing streamlined access to a series of azulene-fused acenes, from mono-azulene-fused anthracene analogue to bis-azulene-fused heptacene analogue. Structural, spectroscopic, and theoretical studies reveal highly planar π-frameworks and pronounced aromaticity redistribution upon π-extension. Progressive fusion perturbs the aromatic 10π azulene perimeter and induces increasing heptafulvene character, strongly modulating the electronic structure. As a result, the bis-azulene-fused pentacene and heptacene analogues exhibit narrow bandgaps comparable to pentacene, yet show remarkably high stability under ambient conditions, with half-lives of 632 and 585 days, respectively. The bis-azulene-fused pentacene analogue delivers a hole mobility of 0.16 cm² V^-1 s^-1, while further extension to the bis-azulene-fused heptacene analogue boosts the mobility to 0.74 cm² V^-1 s^-1, consistent with its planar backbone, low reorganization energy, and efficient π-stacking. In addition, the bis-azulene-fused heptacene analogue displays dual anti-Kasha emission with a fluorescence quantum yield of 4.1%. This work establishes an efficient synthetic entry to stable nonalternant acene analogues and clarifies key structure-property relationships for organic semiconductors and anti-Kasha emissive materials.