Crystalline silicon is a poor UV-visible-near IR emitter because of its indirect, narrow band gap and low quantum yield of ∼1 × 10 -2 % at room temperature. To effectively confine a photoexcited electron-hole pair (exciton) within Si's Bohr radius of ∼5 nm, we have theoretically and experimentally explored several low-dimensional Si-based materials. Although Si-Si bonded network polysilyne was previously regarded as a soluble model polymer of amorphous Si and Si nanosheet-like "saturated silagraphene," further studies on pyrolytic products of polysilyne derivatives and their inherent photophysical properties under a vacuum have not yet been reported. The present paper demonstrated visible light emission from ten soluble polysilynes in the range 460 nm (2.70 eV) to 740 nm (1.68 eV) at both 77 K and room temperature by controlling temperature and time of the pyrolysis (200-500 °C, 10-90 min) under a vacuum. When very weakly deep-red emitting Si particles produced by the pyrolysis of poly(nbutylsilyne) at 500 °C for 90 min were exposed to air, the photoluminescence switched abruptly to an intense sky-blue color (λ ) 430 nm), with a quantum yield of 20-25% and a short lifetime of ∼5 ns in common organic solvents at room temperature because of the Siloxene-like, multilayered Si-sheet structures.
A soluble Si-Si bonded polymer (polysilyne, SNP) bearing n-butyl groups (BSNP) has been reported to exhibit a green photoluminescence (PL) at 540 nm (2.30 eV). However, BSNP gradually changed to a colorless solid because of auto-oxidation within a few weeks when the polymer was stored in the absence of light without special care. Herein, we demonstrate the photophysical properties of SNP carrying 3,3,3-trifluoropropyl (TFP) side groups (FSNP), which remains unaffected by autooxidation. This stability against oxidation may be possibly attributable to intra-and inter-molecular CF-Si interactions between the electron-donating Si-Si main chain and the electron withdrawing TFP side groups. FSNP in polar tetrahydrofuran (THF) exhibited an almost pure-blue PL peak at 450 nm (2.76 eV), whereas in non-polar n-octane, it emitted a near-UV peak at 337 nm (3.68 eV), possibly, because of the CF-Si interactions. Additionally, thin films of FSNP exposed to air and in THF exhibited excellent resistance to air oxidation for at least one month, as determined by the lack of any changes in its PL, IR, and Raman spectra. From Gaussian03 calculations (TD-DFT, 6-31G* basis set, B3LYP) of trans-perhydrosiladecaline partially substituted with TFP and n-butyl groups as models of FSNP and BSNP, the most essential roles of TFP groups suggested that (i) the lowest Sis-Sis* transition state becomes the allowed transition by introducing strong polarity to the SNP skeleton and (ii) both the HOMO and LUMO energy levels are significantly stabilized, which provides the observed stability toward air oxidation. The air stability was effective in copolymers carrying TFP and n-butyl groups (FBSNP). However, FSNP and FBSNP that had been pyrolysed at temperatures greater than 500 C exhibited no such air stability because of the loss of the TFP groups.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.