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π‐Extended Star‐Shaped Polycyclic Aromatic Hydrocarbons based on Fused Truxenes: Synthesis, Self‐Assembly, and Facilely Tunable Emission Properties
Author(s) -
Cheng Cheng,
Jiang Yi,
Liu ChengFang,
Zhang JianDong,
Lai WenYong,
Huang Wei
Publication year - 2016
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.201601355
Subject(s) - bathochromic shift , naphthalene , photochemistry , perylene , naked eye , suzuki reaction , photoluminescence , materials science , intermolecular force , pyrene , ring (chemistry) , absorption (acoustics) , chemistry , molecule , organic chemistry , catalysis , optoelectronics , palladium , physics , chromatography , quantum mechanics , detection limit , fluorescence , composite material
Abstract A new set of star‐shaped polycyclic aromatic hydrocarbons (PAHs) based on naphthalene‐fused truxenes, TrNaC n ( n =1–4), were synthesized and characterized. The synthesis involved a microwave‐assisted six‐fold Suzuki coupling reaction, followed by oxidative cyclodehydrogenation. Multiple dehydrocyclization products could be effectively isolated in a single reaction, thus suggesting that the oxidative cyclodehydrogenation reaction involved a stepwise ring‐closing process. The thermal, optical, and electrochemical properties and the self‐assembly behavior of the resulting oxidized samples were investigated to understand the impact of the ring‐fusing process on the properties of the star‐shaped PAHs. Distinct bathochromic shift of the absorption maxima ( λ max ) revealed that the molecular conjugation extended with the stepwise ring‐closing reactions. The optical band‐gap energy of these PAHs varied significantly on increasing the number of fused rings, thereby resulting in readily tunable emissive properties of the resultant star‐shaped PAHs. Interestingly, the generation of rigid “arms” by using perylene analogues caused TrNaC2 and TrNaC3 to show significantly enhanced 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). Owing to strong intermolecular interactions, the TrNa precursor was able to self‐assemble into rod‐like microcrystals, which could be facilely identified by the naked eye, whilst TrNaC1 self‐assembled into nanosheets once the naphthalene rings had fused. This study offers a unique platform to gain further insight into—and a better understanding of—the photophysical and self‐assembly properties of π‐extended star‐shaped PAHs.