Synthesis and Characterization of host-guest materials with charge transfer complexes of Coumarin:TCNQ inserted into hydrotalcite for LED applications.

Sumeet Kumar ,  Leonardo Marchese ,  Marco Milanesio ,  Enrico Boccaleri 

Università degli Studi del Piemonte Orientale and NANO-Sistemi Interdisciplinary Centre (DISTA), Via V. Bellini 25/G, Alessandria 15100, Italy

Abstract
Recent study of charge transfer (CT) effects on hole injection and device stability in an Organic thin film transistor (OTFT)1and its stability supposedly by the complex formation of poly(9,9-dioctylfluorene-alt-bithiophene) doped with an 8 % of electron-acceptor 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, study of photo-physical features2 and further organization of chromophores into layered double hydrotalcite (LDH) like materials3 motivated us to follow a similar approach.The possible interactions between CT pairs with the LDH host have been investigated. We present the work done in synthesizing luminescent materials based on coumarin-3-carboxylic acid (3CCA) and 7,7,8,8-tetracyanoquinodimethane (TCNQ). An in situ hydrothermal synthesis is carried out to intercalate the 3CCA alone at first and then the CT complex into the LDH Hydrotalcite, following a one-pot synthesis approach. In fact the organic-inorganic hybrid materials have been obtained by dissolving 5 mmol each of 3CCA and TCNQ with 10 mmol of hydrated Aluminium nitrate and 20 mmol of (Zn/Mg) nitrate hydrate salts with at a controlled pH of 7.5±0.5 and CO2 free water solvent. A LDH sample with empirical composition:

[M(II)0.65 M(III)0.35 (OH)2](A-)0.175.nH20], where MII = (Mg2+or Zn2+), MIII = Al3+, and A-= anionic CT complex was obtained. The effect of the M(II) cations was studied by synthesizing Mg/Al HTLc and Zn/AlHTLc [M(II)/M(III) = 2.0]. Finally the samples were washed with decarbonised water, dried at 60 °C and characterized by XRPD/FTIR/IR/FT Raman/UV Vis/TGA techniques. A clear absorption edge with DR-UV-Vis Lambda 900 is observed for the Mg/Al HTLc with 3CCA and with its CT complex with TCNQ (See figure). The [Mg/Al HTLc + CT complex/or 3CCA alone] also shows luminescence in the visible.

final_uv_vis.PNG

Ref:
[1] Hong-Ku et al. / J. Mater. Chem., 2007, 17, 1416-1420.
[2] U. Costantino et al. / J. Mater. Chem., 2002, 12, 3316-3323.
[3] L. Latterini et al. / Inorganica Chimica Acta 360, 2007, 728-740.

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Presentation: Oral at E-MRS Fall Meeting 2008, Symposium B, by Sumeet Kumar
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-05-17 23:23
Revised:   2009-06-07 00:48
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