Effects of Substitution on Solid-State Fluorescence in 9-Aryl-9-methyl-9H-9-silafluorenes

• Main Authors: Yoshinori Yamanoi, Takayuki Nakashima, Masaki Shimada, Hiroaki Maeda, Hiroshi Nishihara
• Format: Article
• Language: English
• Published: MDPI AG 2016-09-01
• Series: Molecules
• Subjects: 9H-9-silafluorene; thiophene; UV absorption; solid-state emission; single-crystal X-ray diffraction; J-aggregation
• Online Access: http://www.mdpi.com/1420-3049/21/9/1173

Aromatic groups were incorporated into 9H-9-silafluorene units at the 9-position (mono-9H-silafluorenes) and 9,9′-positions (di-9H-9-silafluorenes). The aryl substituents showed weak conjugation to the 9H-9-silafluorene for 9-aryl substituted ones 1–7 and a 9,9′-phenylene substituted one (compound 8) and they exhibited similar absorption and emission spectra. The 9H-9-silafluorene 10 containing a 5,5′-(2,2′-bithiophenyl) group showed a significantly red-shifted absorption and fluorescence maxima in the solid-state. Single-crystal X-ray diffraction studies found J-type aggregated structures formed by intermolecular CH–π interactions (ca. 2.6–2.7 Å). Density functional theory (DFT), time-dependent DFT (TD-DFT), and configuration interaction single (CIS) calculations were conducted to explain the observed optical properties.