Journal of Physical Chemistry B, Vol.107, No.44, 12184-12191, 2003
pi-pi and sigma-pi interactions in alpha,omega-di-(9-anthryl) and di-(1-naphthyl) oligosilanes studied by time-resolved fluorescence in solution
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 pi-pi interaction between two aromatic groups and a sigma-pi interaction between aromatics and: a silicon chain unit, were observed. Intramolecular excimer emission was observed in cyclohexane when n greater than or equal to 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 speptra 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 I and 6 in both cyclohexane and acetonitrile.