Photophysical Properties of Silyl‐Substituted Stilbene Derivatives

The effects of silyl groups on the structural, absorption, fluorescence, and photoisomerization properties of stilbenes were investigated. In comparison to that of the parent stilbene ( 1 ), fluorescence quantum yields ( Φ f ) of Me 3 Si‐substituted stilbenes 2–4 and 6 in solution were higher. Derivative 5 , in which Me 3 Si groups are present at all ortho positions of the arene moieties, did not fluoresce at room temperature. The absorption and fluorescence wavelength maxima of Me 3 SiMe 2 Si‐substituted stilbene 7 occurred at longer wavelengths compared to those of the Me 3 Si analog 2 . The results of theoretical calculations showed that this difference is a consequence of an increase in the HOMO energy of 7 caused by orbital interaction between π‐system and the σ(Si–Si) orbital. Stilbene 14 , with two Me 3 Si‐C≡C groups at both para positions, had a high Φ f (0.95). The calculated transition dipole moment ( µ ) was well correlated with Φ f . Derivative 21 , which contains Ph 2 N and Me 3 SiC≡C groups exhibited solvatofluorochromism because it possesses a twisted intramolecular charge transfer (TICT) excited state in which the Ph 2 N group and the aromatic ring are orthogonal.