Nonlinear Optical Properties of Substituted Stilbazolium-MPS 3 Intercalation Compounds
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PASCAL G. LACROIX*, RENE CLEMENT*, KEITARO NAKATANI**, ISABELLE LEDOUX*** AND JOSEPH ZYSS***. *Laboratoire de Chimie Inorganique, U.R.A. 420, Institut de Chimie Moldculaire d'Orsay, Universit6 Paris-sud, 91405 Orsay (France). **Laboratoire de Physicochimie des Rayonnements, Orsay (France). ***C.N.E.T., Bagneux (France).
ABSTRACT We have investigated intercalation into optically transparent MPS 3 (M = Mn, Cd) phases as a way towards spontaneous poling of cationic chromophores. Two nano-composite materials of formula MO. 8 6PS 3 (dimethylamino-N-methyl stilbazolium)0.28 were synthezised, and an efficiency up to 750 times that of urea was recorded in the cadmium intercalate. An additional interest arises from the possibility to associate NLO properties with the magnetization of the host lattice in the case of MnPS 3 below 40 K.
INTRODUCTION It is well known that the main limitation for using molecular compounds exhibiting second order nonlinear optical (NLO) properties is related to their ability to be poled in an acentric structure over a long period of time 1 . By far, the most widely studied method to engineer the chromophores in such an acentric environment is the well documented poled polymer approach. Unfortunatly, this method requires a strong external electric field, and is applicable to neutral chromophores only. The recent discovery of a new class of cationic materials exhibiting extremly high efficiencies 2 could stimulate alternative routes towards spontaneous poling of chromophores without electric fields. Following this goal, we have investigated the intercalation of cationic chromophores into host MPS 3 (M = MnII, CdII) matrix, a family of layered materials, exhibiting a unique, non redox intercalation chemistry based on a cationic exchange 3 ,4 (Fig. 1). The selected chromophore is 4-[4-(dimethylamino)-a-styryl]-l-methyl pyridinium (DAMS+) (Fig. 1).
SYNTHESIS OF THE INTERCALATES The main chemical feature related to the ion exchange process involved in the intercalation chemistry of MPS3 can be summarized by the following equation: MPS 3 + 2x[C+X"] -->Mi-xPS 3 (C2x) + MIx2
613 Mat. Res. Soc. Symp. Proc. Vol. 328. ©1994 Materials Research Society
Van der Waals gap
Figure 1.
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(left) Structure of the MPS3 lamellar materials. It consists of M1 I cations coordinated by 3 (P2S6) 4 - anions which built up the two dimensionnal structure. For clarity, 2 (P2S6)4 - per MII only are drawn in the Figure.(right) Molecular structure of DAMS+.
The mechanism responsible for the intercalation is originated in the very weak Van der Waals interactions between the sulfur layers negatively charged, which allow many cations to be intercalated within a few hours at room temperature, if its size is not too large (e.g. K+, (CH3)4N+, ...). However, much bigger species can be intercalated as well, if the intercalation process is carried out in two steps. A small cation being intercalated first, and then substituted by the appropriate bulky cation. We recently find that DAMS+ could be succesfully interca
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