Design of tetrathiafulvalene-based TPP analogues combining a good electron-donor capacity and a possible organic zeolite formation: A computational investigation Wenliang Li a , Godefroid Gahungu a,1 , Bin Zhang b , Jingping Zhang a, * , Lizhu Hao c a Faculty of Chemistry, Northeast Normal University, 5268 Renmin Street, Changchun 130024, China b Organic Solid Laboratory, CMS Institute of Chemistry, Beijing 100080, China c Key Laboratory for Applied Statistics of MOE, Northeast Normal University, 5268 Renmin Street, Changchun 130024, China article info Article history: Received 27 June 2009 Received in revised form 22 September 2009 Accepted 1 October 2009 Available online 7 October 2009 Keywords: Organic zeolite Tetrathiafulvalene Superconductors Electron donor abstract Tetrathiafulvalene (TTF) and its derivatives are introduced into tris(o-phenylenedioxy)cyclotriphospha- zene (TPP) by substituting side phenyl fragments to design multifunctional materials combining a good electron-donor capacity and a possible inclusion adduct formation. On the basis of accurate calculations (at the PBE0/6-31+G(d,p)//PBE0/6-31G(d,p) level) all the designed compounds were predicted to show the ‘‘paddle wheel” shape, which is one of the key factors responsible for inclusion adducts formation. Furthermore, the electron-donor (E-D) capacity of most of designed molecules was shown to be compa- rable or better than that of commonly used organic superconductors. The feature that their physical prop- erties may be modulated by intercalation of suitable acceptors makes the compounds potential candidates for organic superconductors. Additionally, the new series of compounds with shorter side fragments may form smaller channel diameter, which may provide greater stability for organic zeolites. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Molecular conductors based on radical cations of tetrathiafulva- lene (TTF) and its derivatives have been of major interest in the last two decades [1–5]. Their structures are built on stacks of these flat molecules with large transfer integrals between nearest neighbors to result in band formation, where partial filling due to removal of some of the electrons provide a wide range of ground states rang- ing from superconducting, metallic, spin density wave, charge den- sity wave, charge ordering, and semiconducting. The observation of metallic conductivity at interfaces between layers of organic insu- lators opens the way to the realization of a wide range of electronic systems that cannot be prepared in bulk organic materials. When two crystals of TTF and TCNQ (7,7,8,8,-tetracyanoquinodimethane) were brought into direct mechanical contact, they generated a con- ducting layer with a high carrier density [6]. Using the 1D nanochannels in the tris(o-phenylenedioxy)cyclo- triphosphazene (TPP: Fig. 1i) hexagonal lattice as a template for the molecular arrangement, a series of TPP inclusion compounds with some functional molecules (optical, electrical, and magnetic), have already been prepared [7–12]. TPP/I 2 inclusion compounds exhib- ited electrical conductivity along the nanochannel (r k  10 6 – 10 8 X 1 m 1 , at a potential of 50 V) [7]. In fact, the trigonal arrangement of phosphazene molecules provides a hexagonal channel structure, wherein I 2 , a 2D semiconductor and one of the best characterized n-type molecular donors for the formation of charge-transfer complexes [13], forms chains by inward diffusion and crystallization. Very recently, Yamamoto et al. proposed a new, more complete mechanism for the electrode processes involved, on the basis of the electrochemical and spectroelectro- chemical behavior of thin films of TTF over a glassy carbon elec- trode in iodide media [14]. In our previous works [15,16], on extending the side fragment with fused TTF-like fragment, a series of TPP derivatives showed an electron-donor strength comparable or better than the ones for the commonly known electron donors. In this work, TTF and its derivatives are directly introduced into TPP (Fig. 1ii) by substituting side phenyl fragments on the way to design some new molecules combining the good electron-donor strengths offered by shorter side fragment and the ‘‘paddle wheel” structural characteristic. Indeed, an interesting type of materials may be awaited from such a combination since it would become easier, by a judicious choice of acceptors to be included into the tunnels, to modulate their physical properties including the elec- tric conductivity. On the other hand, the series compounds with shorter side fragment may form smaller channel diameter than the former ones [15,16], and relatively narrow channels with inter- acting walls provide greater stability and thus milder absorption 0166-1280/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.theochem.2009.10.001 * Corresponding author. E-mail address: zhangjingping66@yahoo.com.cn (J. Zhang). 1 Permanent address: Département de Chimie, Université du Burundi, BP 2700 Bujumbura, Burundi. Tel.: +86 431 85098652; fax: +86 431 85099521. Journal of Molecular Structure: THEOCHEM 940 (2010) 13–18 Contents lists available at ScienceDirect Journal of Molecular Structure: THEOCHEM journal homepage: www.elsevier.com/locate/theochem