| Title: |
Conjugation through Si–O–Si bonds, silsesquioxane (SQ) half cage copolymers, extended examples via SiO0.5/SiO1.5 units: multiple emissive states in violation of Kasha's rule. |
| Authors: |
Zhang, Zijing, Arias, Jose Jonathan Rubio, Kaehr, Hana, Liu, Yujia, Murata, Ryoga, Unno, Masafumi, Yodsin, Nuttapon, Pimbaotham, Pimjai, Jungsuttiwong, Siriporn, Rammo, Matt, Heo, Jung-Moo, Kim, Jinsang, Rebane, Aleksander, Laine, Richard M. |
| Source: |
Dalton Transactions: An International Journal of Inorganic Chemistry; 6/28/2024, Vol. 53 Issue 24, p10328-10337, 10p |
| Subject Terms: |
DEGREE of polymerization, RADICAL anions, EMISSION spectroscopy, EXCITED states, CHARGE transfer, POLYMERS, COPOLYMERS |
| Abstract: |
We previously reported that phenyl- and vinyl-silsesquioxanes (SQs), [RSiO1.5]8,10,12 (R = Ph or vinyl) functionalized with three or more conjugated moieties show red-shifted absorption- and emission features suggesting 3-D conjugation via a cage centered LUMOs. Corner missing [PhSiO1.5]7(OSiMe3)3 and edge opened, end capped [PhSiO1.5]8(OSiMe2)2 (double decker, DD) analogs also offer red shifted spectra again indicating 3-D conjugation and a cage centered LUMO. Copolymerization of DD [PhSiO1.5]8(OSiMevinyl)2 with multiple R–Ar–Br gives copolymers with emission red-shifts that change with degree of polymerization (DP), exhibit charge transfer to F4TNCQ and terpolymer averaged red-shifts suggesting through chain conjugation even with two (O–Si–O) end caps possibly via a cage centered LUMO. Surprisingly, ladder (LL) SQ, (vinylMeSiO2)[PhSiO1.5]4(O2SiMevinyl) copolymers offer emission red-shifts even greater for analogous copolymers requiring a different explanation. Here we assess the photophysical behavior of copolymers of a more extreme SQ form: the half cage [PhSiO1.5]4(OSiMe2Vinyl)4, Vy4HC SQs. We again see small red-shifted absorptions coupled with significant red-shifted emissions, even with just a half cage, thus further supporting the existence of pπ–dπ and/or σ*–π* conjugation through Si–O–Si bonds and contrary to most traditional views of Si–O–Si linked polymers. These same copolymers donate an electron to F4TCNQ generating the radical anion, F4TCNQ−. as further proof of conjugation. Column chromatographic separation of short from longer chain oligomers reveals a direct correlation between DP and emission λmax red-shifts as another indication of conjugation. Further, one- and two-photon absorption and emission spectroscopy reveals multiple excited fluorescence-emitting states in a violation of Kasha's rule wherein emission occurs only from the lowest excited state. Traditional modeling studies again find HOMO LUMO energy levels residing only on the aromatic co-monomers rather than through Si–O–Si bonds as recently found in related polymers. [ABSTRACT FROM AUTHOR] |
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| Database: |
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