Synthesis and Characterization of Cyclotri- and Tetrasiloxanes with Pyrenyl Groups

Abstract

Cyclosiloxanes directly bearing polyaromatic groups on silicon atoms have scarcely been reported. Herein, hexa(1pyrenyl)cyclotrisiloxane (2) and octa(1-pyrenyl)cyclotetrasiloxane (3) were successfully prepared from di(1-pyrenyl)silanediol (1) in the presence of a weak base such as tetraethylammonium acetate and triethylamine in MeCN. The structure of the cyclosiloxanes bearing multiple pyrenyl groups in the solid and solution states was evaluated by NMR, X-ray crystallography, and density functional theory (DFT) calculations. All pyrenyl groups of 2 were oriented outward, and no π−π stacking of adjacent pyrenyl groups was observed. However, all pairs of adjacent pyrenyl groups at 1-and 3-positions in 3 are oriented in the same direction and were π−π stacked with respect to each other. The UV−vis spectra of 2 and 3 in organic solvents showed a slight broadening of the peaks, as observed for typical pyrene derivatives. Interestingly, the fluorescence spectra of 2 showed small monomer and strong excimer emissions; however, those of 3 showed only a strong excimer emission in all solvents. Partially pyrenylated cyclotri-and tetrasiloxanes (compounds 4 and 5) showed solvent-dependent monomer and excimer spectra as observed for di(1-pyrenyl)silane derivatives, implying that the excimer emissions of 2 and 3 arise from mainly geminal and vicinal pyrenyl groups, respectively.

Fluorescence Sensing of Anions by Silanediols Bearing Substituted Naphthyl Groups

“…The product analysis revealed that the silanediol 1 a was condensed in the presence of these basic anions to yield the corresponding cyclotetrasiloxane ( 7 a ) as shown in Scheme 4 in MeCN at room temperature. Recently, we have reported the condensation of di(1‐pyrenyl)silanediol to give the corresponding cyclotrisiloxane ( 6 ) and cyclotetrasiloxane ( 7 ) in the presence of weak base such as AcO − or triethylamine at elevated temperature [24] . Therefore, the binding constants of 1 a for AcO − and H 2 PO 4 − could not be determined.…”

“…Recently, we have reported the condensation of di(1pyrenyl)silanediol to give the corresponding cyclotrisiloxane (6) and cyclotetrasiloxane (7) in the presence of weak base such as AcO À or triethylamine at elevated temperature. [24] Therefore, the binding constants of 1 a for AcO À and H 2 PO 4 À could not be determined. However, UV-vis spectra of 1 a with less basic anions such as HSO 4 À , NO 3 À , ClO 4 À , Cl À , Br À , and I À showed smaller but reproducible spectral changes and small quenching of fluorescence spectra of 1 a due to the complexation with these anions.…”