π‐Extended Star‐Shaped Polycyclic Aromatic Hydrocarbons based on Fused Truxenes: Synthesis, Self‐Assembly, and Facilely Tunable Emission Properties

A novel set of star-shaped polycyclic aromatic hydrocarbons (PAHs) based on naphthalenes-fused truxenes, named as TrNaCn (n = 1-4), were synthesized and characterized. Oxidative cyclodehydrogenation was carried out following the microwave-assisted six-fold Suzuki coupling reaction. It is worthwhile to mention that multiple dehydrocyclization samples can be isolated effectively in one reaction, suggesting that the oxidative cyclodehydrogenation was a stepwise ring-closed process. Thermal, optical, and electrochemical properties, and self-assembly behaviors of the resulting oxidized samples were investigated to understand the impact of the ring-fused process on the properties of star-shaped PAHs. Distinct bathochromic shift of the absorption maxima λmax reveals the molecular conjugation extending with the stepwise ring closed reaction going on. The optical band gap energy of these PAHs varied significantly with increasing the fused rings, resulting in facile-tunable emissive properties for the resultant star-shaped PAHs. Interestingly, with the generation of perylene analogue rigid arms, TrNaC2 and TrNaC3 showed significant enhancement of photoluminescence quantum yields (PLQYs) in solution (η = 0.65 and 0.66, respectively) in comparison with those of TrNa and TrNaC1 (η = 0.08 and 0.16, respectively). With strong intermolecular interactions, the precursor TrNa was found to be able to self-assemble into a rod-like crystal which can be facilely identified by naked eyes, while TrNaC1 self-assembled into nanosheets once the naphthalene rings were fused. This study offers a unique platform to gain further insights and better understanding into the photophysical and self-assembly properties of π-extended star-shaped PAHs.