Photophysical Properties of Partially Functionalized Phenylsilsesquioxane: [RSiO1.5]7[Me/nPrSiO1.5] and [RSiO1.5]7[O0.5SiMe3]3 (R = 4‑Me/4-CN-Stilbene). Cage-Centered Magnetic Fields Form under Intense Laser Light

• Published in: Macromolecules Vol. 52; no. 11; pp. 4008 - 4019
• Main Authors: Guan, Jun, Tomobe, Kenji, Madu, Ifeanyi, Goodson, Theodore, Makhal, Krishnandu, Trinh, Minh Tuan, Rand, Stephen C, Yodsin, Nuttapon, Jungsuttiwong, Siriporn, Laine, Richard M
• Format: Journal Article
• Language: English
• Published: American Chemical Society 11.06.2019
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.9b00699

Macromonomers [RPhSiO1.5]8,10,12 and [RCHCHSiO1.5]8,10,12, where R is a conjugated group, have previously been shown to offer photophysical properties wherein excitation promotes an electron from the HOMO to an excited-state LUMO that sits in the center of the cage and allows communication between all conjugated groups, suggesting 3-D delocalization. In the current work, we explore replacing one conjugated group in [RPhSiO1.5]8 with either Me or nPr or simply removing one corner from the cage, [RPhSiO1.5]7(O0.5SiMe3)3, and examine its effect on any potential LUMO that might form. We report here that such changes seem to have no effect on the existence of a 3-D LUMO-derived delocalization as witnessed by emission red-shifts from the R = 4-Me-/4-CN-stilbene moieties essentially identical to those for the original [RPhSiO1.5]8 macromonomers. Of particular importance is the fact that removing one corner from the cage also has little effect on the photophysics, indeed significantly improving fluorescence emission quantum efficiencies. However, removing most of the conjugated groups on the corner missing cage (from 7 to 2), e.g., [MeStilSiO1.5]2[PhSiO1.5]5(O0.5SiMe3)3, eliminates the red-shift, implying the absence of a LUMO inside the cage. This suggests a minimum number of groups are needed to form such a LUMO. Also, for the first time, the radiation patterns for nonlinear, optically induced magnetic scattering at elevated light intensities are reported for these compounds and shown to support the same conclusiona spherical LUMO exists inside the cage.