Ring‐Shaped Silafluorene Derivatives as Efficient Solid‐State UV‐Fluorophores: Synthesis, Characterization, and Photoluminescent Properties

Abstract

Four ring-shaped silafluorene-containing compounds (1-4) were synthesized and characterized as potentially promising monomers for fluorescent polymers. Their optical properties in solution and solid state (thin film and powder) were studied. These compounds have low quantum yields in solution (Φ(fl)=0.13-0.15) with fluorescence maxima at about 355 nm, but high quantum yields in the solid state (powder, Φ(fl)=0.35-0.54) with fluorescence maxima at about 377 and 488 nm. Influence of the substituents and the number of silafluorene units in 1-4 on their optical properties was investigated. Extensive study of the X-ray crystal structures of 1-4 was undertaken to analyze and qualitatively estimate the role, extent, and influence of silafluorene moieties' interactions on solid-state fluorescent properties. Excited state UV/Vis and theoretical molecular orbital (MO) calculations were performed to explore possible fluorescence mechanisms and differences in quantum yields among these compounds.

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

“…All the chromophores displayed fluorescence quantum yields of φ = ca. 0.1 in n -hexane, consistent with values previously reported for 9 H -9-silafluorenes [20,21,22].…”

High solid-state fluorescence in ring-shaped AEE-active tetraphenylsilole derivatives

“…Although most bond lengths and bond angles of the silole unit in 1-3 are very similar to those found in other silole-containing counterparts (ESI, † Table S2), the C-Si silole -C bond angles (93.801-94.771) are all larger than those observed in the silafluorene-containing cyclosiloxanes (92.61-93.431). 30 We attribute the widening of the C-Si silole -C bond angle to the increased steric clash of the phenyl substituents on the silole group. In general, the cyclosiloxane rings of 1-3 are more nearly planar than those of the silafluorene-containing compounds.…”

“…Recently, we discovered that silafluorene-containing ringshaped siloxanes a and b (Scheme 1), accessible through a simple co-hydrolysis reaction of 9,9-dichloro-9-silafluorene and the corresponding dichlorosilane derivatives under ambient conditions, display superior solid-state fluorescence properties. 30 Our preliminary analysis revealed that their fluorescence is primarily influenced by the unique way the molecules are packed in the unit cell as well as the electronic properties of the fluorophore moieties. We were thus interested in extending our studies of ring-shaped silole-containing molecules by synthesizing a new class of blue light emitting compounds incorporating tetraphenylsilole as a fluorogenic unit.…”

Synthesis and characterization of luminescent 2,7-disubstituted silafluorenes

“…47 Previously, they reported a series of four ring-shaped siloxane derivatives containing silafluorene units that showed his quantum efficiency in the solid state (Φ f = 0.35-0.54). 48 Pusztai and coworkers synthesized two highly fluorescent blue-emitting bis(diquinaldinatoalumino)-9-silafluorenes that exhibited high quantum efficiency in solution and in the solid-state. 49 All of the new silafluorenes were observed to have strong blue emission both in solution and the solid state, whose physical properties vary upon the alkynyl(aryl) linkages employed.…”