The photophysical properties of two series of oligosilanes, (1-naphthyl)-(SiMe2)
n
-(1-naphthyl) (1−5) and
(9-anthryl)-(SiMe2)
n
-(9-anthryl) (6−10) with n = 1−4 and 6, were investigated. In these compounds, two
types of interactions, a π−π interaction between two aromatic groups and a σ−π interaction between aromatics
and a silicon chain unit, were observed. Intramolecular excimer emission was observed in cyclohexane when
n ≥ 2. The strongest excimer emission of 2 and 7 is different from the Hirayama rule (n = 3) proposed for
carbon analogues and also shows that intramolecular cycloaddition is minor. The time-resolved fluorescence
spectra of an anthryl series revealed that the time constant of excimer formation varied depending on the
chain length (82−152 ps). In the cases of 4, 5, and 10, charge-transfer (CT) emission was observed in
acetonitrile or THF. The time constant of the CT-state formation for 10 was relatively slow (45 ps), which
may indicate a conformational change. Monomer emission from the locally excited state was observed for 1
and 6 in both cyclohexane and acetonitrile.
The π–π and σ–π interactions in α,ω-di-1-naphthyl and -di-9-anthryl oligosilanes [Np–(SiMe2)n–Np (1–4), Ant–(SiMe2)n–Ant (5–8), n = 1–4] were investigated in solution. In nonpolar solvents such as cyclohexane, a strong excimer fluorescence is observed, which indicates a strong π–π interaction. In a polar solvent (CH3CN), a charge-transfer (CT) emission is observed for 3 and 4 due to the σ–π interaction.
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