Why do the [PhSiO<sub>1.5</sub>]<sub>8,10,12</sub>cages self-brominate primarily in the ortho position? Modeling reveals a strong cage influence on the mechanism

Bahrami, Mozhgan; Hashemi, Hossein; Ma, Xiao; Kieffer, John; Laine, Richard M.

doi:10.1039/c4cp03997a

Cited by 19 publications

(36 citation statements)

References 37 publications

(38 reference statements)

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“…We believe that similar interactions arise between the extended cage LUMOs and ortho-substituted moieties conjugated to the cage as supported by the work discussed below and published previously. 39 Feher and Budzichowski report 13 C chemical shifts for [RphenylSiO 1.5 ] 8 in parallel with their Hammett substituent Scheme 2. Heck Coupling Synthesis of (RStyr) x (PhSiO 1.5 ) 10 from (Br) x (PhSiO 1.5 ) 10 (x ≈ 3 or 8)…”

Section: ■ Results and Discussionmentioning

confidence: 96%

Synthesis and Characterization of Nanobuilding Blocks [o-RStyrPhSiO_1.5]_10,12 (R = Me, MeO, NBoc, and CN). Unexpected Photophysical Properties Arising from Apparent Asymmetric Cage Functionalization as Supported by Modeling Studies

et al. 2015

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The photophysics of [o-4-RStyrPhSiO 1.5 ] 8 [R = Me, OMe, NBoc, and CN] was reported previously. Here we report studies on [o-4-RStyrPhSiO 1.5 ] 10,12 , [o-4-RStyrPhSiO 1.5 ] 3− [PhSiO 1.5 ] 7 , and [o-4-RStyrPhSiO 1.5 ] 6 [PhSiO 1.5 ] 6 to explore cage size, geometry, and partial substitution effects on photophysical properties. All compounds were characterized by traditional methods including solution spectroscpy and two-photon absorption (TPA) cross sections and except R = NBoc offer T d5% ≥ 400°C/air. All exhibit absorption and emission spectra similar to the T 8 cages but with some important differences in TPA cross sections. The R-stilbenes appear to interact in the excited state through the cage, exhibiting emission spectra redshifted from the parent stilbenes. TPA studies show novel behavior that is functional group, geometry, and substitution number dependent. Thus, NBoc TPA cross sections/moiety increase, with decreasing numbers of functional groups from 8 to 3 for PhT 10 and 10 to 6 for PhT 12 where [NBocStyrPhSiO 1.5 ] 8 TPA/moiety ≈0. In contrast, CN cages offer TPA/moiety values slightly greater on going from 3 to 8 (PhT 10 ) and 6 to 10 (PhT 12 ). NBoc TPA data are best explained if bromination occurs asymmetrically, leading to asymmetric functionalization and exceptional polarization in partially substituted cages as symmetrically substituted cages exhibit opposing polarizations. In sum, all the individual induced transition dipoles on excitation mutually cancel. In contrast, both the cage and CN are strongly electron withdrawing such that no significant polarization is observed/expected when asymmetrically functionalized. Both NBoC and CN substituents offer red shifts greater than Me and MeO T 10,12 , suggesting extended conjugation without polarization. Asymmetric bromination is supported by DFT modeling studies where initial o-Br/o-H bonding stabilizes incoming Br 2 by 300 mEv.

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Section: ■ Results and Discussionmentioning

confidence: 96%

Synthesis and Characterization of Nanobuilding Blocks [o-RStyrPhSiO_1.5]_10,12 (R = Me, MeO, NBoc, and CN). Unexpected Photophysical Properties Arising from Apparent Asymmetric Cage Functionalization as Supported by Modeling Studies

et al. 2015

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“…General Heck Reaction of Brominated and Iodinated Ph 7 T 8 R′ and Ph 7 T 7 -Trisiloxy. 23,27 To a dry 100 mL Schlenk flask under N 2 were added brominated or iodinated Ph 7 T 8 R′ or Ph 7 T 7trisiloxy (1.0 mmol), Pd[P(t-Bu 3 )] 2 (38.7 mg, 0.08 mmol), and Pd 2 (dba) 3 (34.6 mg, 0.04 mmol), followed by 30 mL of THF, NCy 2 Me (2.8 g, 14.0 mmol), and 4-methyl/cyanostyrene (14.0 mmol). The mixture was stirred magnetically at 70 °C for 24 h and then quenched by filtering through 1 cm Celite, which was washed with THF (5 mL).…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

“…We find that the cage-centered LUMO engages an incoming Br 2 and together with hydrogen bonding to ortho hydrogens leads to formation of an energetically favored transition state akin to a Venus flytrap that selectively drives ortho bromination (Figure 1). 23 More recently, we reported that the first bromine on the cage promotes bromination on the same face of the cage as illustrated in Figures 2 and 3. 24 The crystal structure in Figure 3 shows that careful bromination allows the synthesis and isolation of a Janus brominated cage.…”

Section: ■ Introductionmentioning

confidence: 99%

Photophysical Properties of Partially Functionalized Phenylsilsesquioxane: [RSiO_1.5]₇[Me/nPrSiO_1.5] and [RSiO_1.5]₇[O_0.5SiMe₃]₃ (R = 4-Me/4-CN-Stilbene). Cage-Centered Magnetic Fields Form under Intense Laser Light

et al. 2019

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Macromonomers [RPhSiO 1.5 ] 8,10,12 and [RCH CHSiO 1.5 ] 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 [RPhSiO 1.5 ] 8 with either Me or nPr or s i m p l y r e m o v i n g o n e c o r n e r f r o m t h e c a g e , [RPhSiO 1.5 ] 7 (O 0.5 SiMe 3 ) 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 redshifts from the R = 4-Me-/4-CN-stilbene moieties essentially identical to those for the original [RPhSiO 1.5 ] 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., [MeStilSiO 1.5 ] 2 [PhSiO 1.5 ] 5 (O 0.5 SiMe 3 ) 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.

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“…1). Closed cages are usually called POSS, i.e., polyhedral oligomeric silsesquioxanes, and indicated by the notation T m n , where m is the number of oxo-bridges and n is an even number ranging from 6 to 18 that accounts for the Si atoms present in the cage (Voronkov and Lavrent'yev 1982;Sellinger and Laine 1996;Laine 2005;Bahrami et al 2014), the most popular POSS being T 3 8 (Itoh 2014). The ordered silicon-based core of POSS is considered the smallest existing silica network, with sizes in the range 1-3 nm (Kickelbick 2014).…”

Section: Introductionmentioning

confidence: 99%

Architecture of Silsesquioxanes

Dirè

Borovin

Ribot

2016

Handbook of Sol-Gel Science and Technology

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Why do the [PhSiO_1.5]_8,10,12cages self-brominate primarily in the ortho position? Modeling reveals a strong cage influence on the mechanism

Cited by 19 publications

References 37 publications

Synthesis and Characterization of Nanobuilding Blocks [o-RStyrPhSiO_1.5]_10,12 (R = Me, MeO, NBoc, and CN). Unexpected Photophysical Properties Arising from Apparent Asymmetric Cage Functionalization as Supported by Modeling Studies

Synthesis and Characterization of Nanobuilding Blocks [o-RStyrPhSiO_1.5]_10,12 (R = Me, MeO, NBoc, and CN). Unexpected Photophysical Properties Arising from Apparent Asymmetric Cage Functionalization as Supported by Modeling Studies

Photophysical Properties of Partially Functionalized Phenylsilsesquioxane: [RSiO_1.5]₇[Me/nPrSiO_1.5] and [RSiO_1.5]₇[O_0.5SiMe₃]₃ (R = 4-Me/4-CN-Stilbene). Cage-Centered Magnetic Fields Form under Intense Laser Light

Architecture of Silsesquioxanes

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Why do the [PhSiO1.5]8,10,12cages self-brominate primarily in the ortho position? Modeling reveals a strong cage influence on the mechanism

Cited by 19 publications

References 37 publications

Synthesis and Characterization of Nanobuilding Blocks [o-RStyrPhSiO1.5]10,12 (R = Me, MeO, NBoc, and CN). Unexpected Photophysical Properties Arising from Apparent Asymmetric Cage Functionalization as Supported by Modeling Studies

Synthesis and Characterization of Nanobuilding Blocks [o-RStyrPhSiO1.5]10,12 (R = Me, MeO, NBoc, and CN). Unexpected Photophysical Properties Arising from Apparent Asymmetric Cage Functionalization as Supported by Modeling Studies

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

Architecture of Silsesquioxanes

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Why do the [PhSiO_1.5]_8,10,12cages self-brominate primarily in the ortho position? Modeling reveals a strong cage influence on the mechanism

Synthesis and Characterization of Nanobuilding Blocks [o-RStyrPhSiO_1.5]_10,12 (R = Me, MeO, NBoc, and CN). Unexpected Photophysical Properties Arising from Apparent Asymmetric Cage Functionalization as Supported by Modeling Studies

Synthesis and Characterization of Nanobuilding Blocks [o-RStyrPhSiO_1.5]_10,12 (R = Me, MeO, NBoc, and CN). Unexpected Photophysical Properties Arising from Apparent Asymmetric Cage Functionalization as Supported by Modeling Studies

Photophysical Properties of Partially Functionalized Phenylsilsesquioxane: [RSiO_1.5]₇[Me/nPrSiO_1.5] and [RSiO_1.5]₇[O_0.5SiMe₃]₃ (R = 4-Me/4-CN-Stilbene). Cage-Centered Magnetic Fields Form under Intense Laser Light