Photoluminescence of as‐synthesized and heat‐treated phenyl‐containing polysilylcarbodiimides: role of crosslinking and free carbon formation in polymer‐derived ceramics

Abstract

For the first time, photoluminescence properties of four polysilylcarbodiimides, comprised of a phenyl pendant group attached at the silicon atom and a second substituent being either phenyl (S1), methyl (S2), hydrogen (S3) or vinyl (S4), are reported. Distinctive fluorescence emissions are detected in the polymers with one phenyl group at the silicon atom (S2, S3 and S4), due to a phenyl excimer emission. The polymer with two phenyl groups attached at the same silicon atom (S1) shows, besides the phenyl excimer emission, also a vibrationally structured emission stemming from the Ph-SiX 2 -Ph unit. Moreover, the polysilylcarbodiimides were heat-treated at different temperatures up to 500 C in argon flow. In this case, the amount of crosslinking is identified to be responsible for a bathochromic shift of the maximum emission spectra with increasing annealing temperature. After annealing at 300 C, polymers S2 and S3 present a red-shifted emission due to rearrangement reactions of the basic polymer structure. Furthermore, the presence of free carbon formed during the annealing procedure in the form of polycyclic aromatic hydrocarbons, as well-defined fragments of graphene, are proven to contribute to the photoluminescence properties of the heat-treated polysilylcarbodiimides.

Formation and Luminescent Properties of Al2O3:SiOC Nanocomposites on the Base of Alumina Nanoparticles Modified by Phenyltrimethoxysilane

“…A strong and broad absorption band in range of 980–1200 cm −1 and centered at 1033 cm −1 is obviously due to siloxane bonds. A similar band was observed in phenyl-siloxane based polymers and associated with crosslinking of siloxane bonds into network [16, 17]. This band indicates formation of polymer-like siloxane precipitates on the surface of Al 2 O 3 particles during chemical treatment procedure.…”

“…Such materials can be indicated as Al 2 O 3 /SiOC. Mechanism of formation of SiOC surface precipitates is believed to be similar to polymerization and structural crosslinking in polymer-derived SiOC ceramics obtained from phenyl-containing organosilicon precursor [17]. It is important also to note that pristine alumina annealed at the same conditions does not show any noticeable photoluminescence.…”

Synthesis and high-temperature evolution of polysilylcarbodiimide-derived SiCN ceramic coatings

“…The formation of its branched structure probaly relies on disproportionation reactions of H 3 C(H)SiCl 2 to furnish H 3 CSiCl 3 and H 3 C(Cl)SiH 2 , as also reported in [16][17][18]. Interestingly, the reaction reported in the literature (i.e., H 3 C(H)SiCl 2 with bis(trimethylsilyl) carbodiimide) leads to the formation of an insoluble [-SiCH 3 (NCN)-1,5 ] n gel network [16][17][18]; whereas in the present study the addition of a second chlorosilane, i.e. H 3 C(Vi)SiCl 2 , allows for limiting the branching of the polymer and thus generates a soluble preceramic polymer with a branched molecular structure.…”

“…However, it is not clear if this is related to the higher segregated carbon content in the PV-based samples (70 vol%), as compared in the MHMV-based ceramics, (to 40 vol%, see Table 2), or to the different molecular structures of PV and MHMV, since the polymer structure and particularly the organic substituents at silicon (see Fig. 1) is directly involved in the formation of the free carbon phase during the ceramization process [18]. Fig.…”

Synthesis and characterization of luminescent properties of ceramics derived from polysilylcarbodiimides

“…17) The reason for the black color of the PDC has been generally ascribed to the presence, in the ceramic structure of free carbon. 18) For this reason, optical properties of the PDCs, especially the polymerderived ternary SiCN materials are scarcely exploited since the absorption of visible light, which hinders their capability for the production of optical devices.…”