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Self-Assembled bis(amino acid)-2, 6- and 1, 4- naphthalene amide gelators as a scaffolds for Fluorescence Resonance Energy Transfer (FRET)

Recent study in a field of supramolecular gels resulted in the development of recognizable areas in materials chemistry with an emphasis on the self-organizing soft materials.1, 2 They have a great opportunity for specific applications in various fields, such as optoelectronics, light harvesting, organic– inorganic hybrid materials, pharmaceutical, food and cosmetic industry or in tissue engineering. pi-conjugated chromophores are promising candidates for next generation electronic devices.3 Our attention was focused on the synthesis and investigations of the properties of self-assembly, photophysical studies and energy transfer in a bis-amide functionalized 2, 6- and 1, 4-naphthalene dicarboxylic acid based organogel. The Gly, Ala and Phe derivatives were synthesized and characterized. Due to the synergistic effect of hydrogen bonding, pi–pi stacking and hydrophobic interaction, this gelators showed long-range ordering in a non-polar solvent, as evidenced by the fibrous morphology observed in TEM. These compounds showed gelation in various organic solvents with very low critical gelation concentration (<0.1 wt%). Evidence for hydrogen bonding was further probed by a variable temperature NMR. UV/vis and photoluminescence studies of the gel indicated offset pi-stacking between the gelators chromophores. Bis-amide functionalized dialkoxynaphlane derivatives and pyrene are known to form an efficient D–A pair.4 The bis(Ala)-1, 4-naphthalene amide gel was tested in presence of pyrene for FRET, photoluminescence properties of naphthalene was quenched. It was found that the fluorescence from the donor turn strong emission was observed from pyrene suggesting a very efficient FRET process possibly due to close proximity of the pyrene acceptor and the bis(Ala)-1, 4-naphthalene amide as a chromophore in the gel state.

Supramolecular gels ; Fluorescence Resonance Energy Transfer (FRET)

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