Self-assembly-based Thermo-responsible Luminescent Organogels of Chromophoric L-glutamide-derived Lipids
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Makoto Takafuji Department of Applied Chemistry and Biochemistry, Kumamoto University, Kumamoto 860-8555, Japan
Hiroshi Hachisako Department of Applied Life Science, Sojo University, Kumamoto 860-0082, Japan
Takashi Sagawa Institute of Advanced Energy, Kyoto University, Uji 611-0011, Japan
Hirotaka Iharaa) Department of Applied Chemistry and Biochemistry, Kumamoto University, Kumamoto 860-8555, Japan (Received 21 February 2005; accepted 25 May 2005)
Three lipophilic L-glutamide derivatives with chromophoric head group were synthesized, and their photo-responsive properties were investigated in organic solution systems. By comparing their spectral behaviors, it was shown that organogels underwent a light blue to purple luminescence change, which was triggered by thermally induced monomeric-to-excimeric phase transition. This switching, based on self-assembly, is supposed to have special advantages in molecular electronics.
I. INTRODUCTION
Recently organogel systems and their applications have become topical issues in nano-science.1–3 These systems, composed of trapped solvent in a network of solute, are brought about by weak intermolecular interactions like hydrogen bonding, van der Waals forces and – stacking. Thanks to these relatively weak intermolecular interactions, they can be influenced by some external stimuli like temperature and light and consequently can be considered stimuli-responsive smart materials. Optical sensors, switches, and energy sources for molecular electronics are examples of putative applications of these stimuli-responsive compounds. Introducing a suitable chromophoric group to organogelators is an effective strategy for finding new photosensitive systems.4–6 We have already reported different kinds of organogelators and discussed the key role of glutamide-derived lipid in self-assembly and gel formation.7,8 In our reports, organogelators have a chiral center (␣-carbon of L-glutamide) and three amide moieties that promote their self-assembly by hydrogen bonds. Furthermore, they possess an amino group to introduce different functional head groups to the molecule a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0296 2486
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 9, Sep 2005 Downloaded: 24 Mar 2015
to develop desired functions in organogel. In this new research, we introduce three kinds of organogelators containing photo-active head groups to evaluate and compare their luminescence impact (Scheme 1). Lipophilic L-glutamide was conjugated with pyrene, dimethylaniline, and pyrene-E, and thermo-responsible spectral behavior of their simple and mixed resultant organogels was studied. Our attention is paid to these molecular systems because their spectral properties can be reversibly controlled by using stimuli such as heating, which suggest new applications in molecular optics. II. EXPERIMENTAL SECTION A. N 1,N 5-didodecyl-N 2-[4-(1-pyrenylbutyroyl)]-Lglutamine (Pyr)
N 1 ,N 5 -didodecyl-N 2 -[4-(1-pyrenylbutyroyl)
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