Crystal structure and novel solid-state fluorescence behavior of the model benzoxazine monomer: 3,4-Dihydro-3,6-dimethyl-1,3, 2H-benzoxazine Worawat Wattanathana a , Sutharat Nonthaglin b , Chatchai Veranitisagul c , Nattamon Koonsaeng a , Apirat Laobuthee b,⇑ a Department of Chemistry, Faculty of Science, Kasetsart University, Ladyao, Chatuchak, Bangkok 10900, Thailand b Department of Materials Engineering, Faculty of Engineering, Kasetsart University, Ladyao, Chatuchak, Bangkok 10900, Thailand c Department of Materials and Metallurgical Engineering, Faculty of Engineering, Rajamangala University of Technology Thanyaburi, Pathumthani 12110, Thailand highlights  Crystal structure of 3,4-dihydro-3,6- dimethyl-1,3,2H-benzoxazine (MM) was reported.  Structure parameters of MM were compared with previous literatures.  Solid-state fluorescence behavior of MM was firstly investigated. graphical abstract article info Article history: Received 26 March 2014 Received in revised form 21 May 2014 Accepted 23 May 2014 Available online 4 June 2014 Keywords: Benzoxazine monomer X-ray crystallography Fluorescent spectroscopy abstract Solid-state fluorescent behavior of the model benzoxazine monomer, 3,4-dihydro-3,6-dimethyl-1,3, 2H-benzoxazine denoted as MM, was firstly reported. Three characteristic fluorescence peaks were observed, i.e., (1) the ultraviolet peak at 317 nm with the excitation wavelength of 258 nm, (2) the blue emission peak at 450 nm with the excitation wavelength of 324 nm and (3) the other blue fluorescent peak at 454 nm with the excitation wavelength of 360 nm. It was proved that the benzoxazine core was responsible for the fluorescence of blue light due to the absence of the emission peak in the ring-opening benzoxazine dimer with the same moieties as the benzoxazine monomer MM. The single crystal X-ray structure of the compound MM recorded at 100 K showed that the irregular chair confor- mation of the ring-closure benzoxazine MM gave rise to the fluorescent property since all the members of the oxazine ring other than nitrogen atom arranged themselves at the plane of the benzene ring. Ó 2014 Elsevier B.V. All rights reserved. Introduction Benzoxazines are a sort of heterocyclic compounds which have the core structure of benzene ring fused with oxazine ring which can readily synthesized by the Mannich reaction of mixing three components, namely, primary amines, paraformaldehyde, and phenols [1–5]. Many possible combinations of the precursors are available leading to the diversity of molecular design. The desired properties of the benzoxazine monomers can be accomplished by adjusting their functional and substitution groups. Moreover, the importance of these compounds is for producing the corresponding http://dx.doi.org/10.1016/j.molstruc.2014.05.057 0022-2860/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +66 27970999. E-mail address: fengapl@ku.ac.th (A. Laobuthee). Journal of Molecular Structure 1074 (2014) 118–125 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc