Photoluminescence of as-synthesized and heat-treated phenyl-containing polysilylcarbodiimides: role of crosslinking and free carbon formation in polymer-derived ceramics Gabriela Mera a *, Ilaria Menapace a , Scarlett Widgeon b , Sabyasachi Sen b and Ralf Riedel a 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. Copyright © 2013 John Wiley & Sons, Ltd. Keywords: polysilylcarbodiimides; photoluminescence; crosslinking; polycyclic aromatic hydrocarbons; polymer-derived ceramics Introduction Since the work of Ebsworth, Wannagat and Birkofer on the synthesis of silylcarbodiimides, [1–5] several monomeric and polymeric deriva- tives have been reported. Organosilylcarbodiimides have been discussed for applications as stabilizing agents for polyurethanes and polyvinylchloride, as insulator coatings, high-temperature sta- ble pigments [6] and as irradiation-resistant sealing materials. [7] Moreover, polysilylcarbodiimides have been used for the synthesis of organic cyanamides, carbodiimides and heterocycles. [8] Polysilylcarbodiimides are generally air- and moisture-sensitive materials. [9] By insertion of bulky aromatic substituents at silicon, the air sensitivity decreases significantly. [10] Here we report on the photoluminescence properties of four poly(phenylsilylcarbodiimide) derivatives, namely -[PhRSi-NCN] n -, S1–S4, synthesized by the reaction of phenyl-containing dichlorosilanes with bis (trimethylsilylcarbodiimide) in the presence of pyridine as cata- lyst. The first substituent on the silicon is phenyl in all polymers, while the second substituent is varied between hydrogen, methyl, vinyl and phenyl. [10,11] Phenyl-containing polysilylcarbodiimides were previously reported to be suitable precursors for high-temperature stable nanostructured carbon-rich silicon carbonitride-based ceramics, [10–18] e.g. for anode materials in Li-ion batteries. [19,20] In general, phenyl-containing polycarbosilanes and polysiloxanes have been shown to provide luminescence properties. [21–23] In a previous paper, we reported on the photoluminescence proper- ties of two commercially available polysiloxane and polysilazane glass-like materials with emission ranges dependent on the treatment temperatures. [24] In the present paper, the photoluminescence properties of polylsilylcarbodiimides are presented for the first time. Further- more, the polysilylcarbodiimides were heat-treated in argon at different temperatures, from 200  C up to 500  C for 2 h under Ar flow, at a heating rate of 50  Ch 1 , and allowed to furnace cool. After low-temperature treatments, the polymers showed distinctive luminescence properties, which are of interest for different applications, i.e. smart windows, LEDs, etc. Furthermore, the polymers S1–S4 are soluble in all common solvents and therefore easy to shape either as synthesized or after heat treatment up to 400  C. * Correspondence to: G. Mera, Technische Universität Darmstadt, Fachbereich Material- und Geowissenschaften, Petersenstrasse 32, Darmstadt, D-64287, Germany. E-mail: mera@materials.tu-darmstadt.de a Technische Universität Darmstadt, Fachbereich Material- und Geowissenschaften, Darmstadt, D-64287, Germany b Department of Chemical Engineering and Materials Science, University of California at Davis, Davis, CA, 95616, USA Appl. Organometal. Chem. (2013) Copyright © 2013 John Wiley & Sons, Ltd. Special Issue Article Received: 25 July 2012 Revised: 5 February 2013 Accepted: 6 February 2013 Published online in Wiley Online Library (wileyonlinelibrary.com) DOI 10.1002/aoc.2993 1