DFT analysis of vibrational spectra of phosphorus-containing dendrons built from cyclotriphosphazene core V.L. Furer a, * , I.I. Vandyukova b , A.E. Vandyukov b , S. Fuchs c , J.P. Majoral c , A.M. Caminade c , V.I. Kovalenko b, * a Kazan State Architect and Civil Engineering University, Zelenaya, 1, Kazan 420043, Russia b A.E. Arbuzov Institute of Organic and Physical Chemistry, Russian Academy of Science, Arbuzov Str., 8, 420088 Kazan, Russia c Laboratorie de Chimie de Coordination, CNRS, 205 route de Narbonne, 31077 Toulouse Cedex 4, France article info Article history: Received 29 April 2009 Received in revised form 25 May 2009 Accepted 26 May 2009 Available online 31 May 2009 Keywords: Phosphorus-containing dendrons IR spectra Raman spectra DFT abstract FTIR and FT-Raman spectra of phosphorus-containing dendrons built from the hexafunctional cyclotri- phosphazene core with five terminal aldehyde (G 0 0 ) or P–Cl (G 0 ) groups and one ester function have been recorded and analyzed. The optimized geometry, frequencies and intensity of IR bands of dendrons were obtained by the density functional theory (DFT). It was found that the internal skeleton of G 0 , G 0 0 mole- cules exists in a single stable conformation with slightly non-planar cyclotriphosphazene core. But termi- nal ester group in G 0 molecule may adopt flat and chair rotational isomers. The flat conformer is 0.04 kcal/mol less stable compared to the chair conformer. The bond lengths and bond angles obtained by DFT show the best agreement with experimental data. Relying on DFT calculations a complete assign- ment of vibrations is proposed for different parts of dendrons. The calculated frequencies and intensity of bands in the IR spectra of dendrons are found to be in reasonable agreement with the experimental results. Our study reveals that the most reactive site in G 0 is the PCl 2 terminal groups. The local softness of C@O bond of benzaldehyde in G 0 0 is higher than that of methylbenzoate group. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Molecules of dendrimers have three-dimensional structure con- sisting of dendritic wedges (dendrons) that proceed from one cen- tre – the core with exponentially increasing number of repeated units and terminal groups depending on generation number [1–3]. The ability to tune the size, topology, molecular weight and properties of dendrimers has led to their widespread use in a variety of applications from biology to material science [1–3]. Dendrons are dendritic macromolecules having one function lo- cated at the core and several other functions located on the surface. Depending on the type of this function, several dendrons can be associated by their core in a spontaneous self-assembly, or by reac- tion with a multifunctional core [4,5]. The special macromolecular architectures called ‘‘layer-block”, ‘‘segment-block” or ‘‘surface- block” dendrimers have been obtained using dendrons [6,7]. The synthesis of ‘‘Janus” dendrimers bearing fluorescent entities on one side and water-solubilizing functions on the other, which should be useful for labelling materials or biological entities was described [8]. The key point for the synthesis such dendrimers is the coupling of two different dendrons by their core. The use of dendrons built from the hexafunctional cyclotriphosphazene core enables one to rapidly multiply the number of terminal groups. The strategy is based on the nonsymmetrical functionalization of hexachlorotri- phosphazene (N 3 P 3 Cl 6 ) to synthesize AB 5 type compounds, where A is the function usable for the coupling with another dendron and B is the functional terminal group; thus, five functions remain available for growing, instead of two for ‘‘classical” dendrons [8]. IR and Raman spectra study combined with DFT calculations is important for investigation of phosphorus-organic dendrimers as containers for different guest molecules. It enables one to reveal the active sites for nucleophilic and electrophilic attack. The calcu- lated electronic density spatial distribution reveals the regions where appropriate environments would attract either an ion or a metal atom. The interpretation of IR spectra of non-crystalline den- drimers is important for their structural characterization. The rather rigid repeating unit, having small conformational flexibility, defines the perfect microstructure of studied phosphorus-organic dendrimers up to the eleventh generation. The analysis of band- widths in the IR and Raman spectra enables one to characterize the flexibility of repeated units and terminal groups of dendrimers. The disk-like shape of molecules allows the uniform dendron arrangement, which has no appreciable spatial hindrances up to very high generations [9,10]. The quantum chemical calculations 0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2009.05.044 * Corresponding authors. Tel.: +7 843 51047 37; fax: +7 843 2387972 (V.L. Furer); tel.: +7 843 2732283; fax: +7 843 2732253 (V.I. Kovalenko). E-mail addresses: furer@ksaba.ru (V.L. Furer), koval@iopc.knc.ru (V.I. Kovalenko). Journal of Molecular Structure 932 (2009) 97–104 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc