Self-sustaining, fluorescent and semi-conducting co-assembled organogel of Fmoc protected phenylalanine with aromatic amines

Abstract

N-Flourenylmethoxycarbonyl (Fmoc) phenylalanine (F) produces co-assembled organogel with 2-aminoanthracene (AA) and 2-aminonaphthalene (NA) at a 1 : 1 molar ratio of the components. The deep green co-assembled F-AA gel is rigid and can be cut into different shapes. At lower concentration, 0.2% (w/v), it shows a mixture of fibre and flake morphology, while at 1.5% (w/v) concentration only flake morphology is observed but the F-NA co-assembled gel produces tape morphology. The powder diffraction data of F-AA co-assembled gel indicate π–π stacking and lamellar packing which is supported by DFT calculation. The melting point of F gel is 15 °C higher over F-AA gel but the gel strength and stiffness of the F-AA co-assembled gel is 94 and 2.5 times higher than that of F gel. The F gel shows a smooth gel breaking point at 4 Pa but the F-AA co-assembled gel shows only a slippage at 160 Pa due to its high stiffness. The UV-vis spectra suggest the formation of H-aggregates and a charge transfer complex in the F-AA gel. The emission peak of AA shows a red shift in the F-AA co-assembled gel where both fluorescence intensity and peak position decrease with an increase in temperature. The F-AA xerogel shows semiconducting behaviour with a dc conductivity value 2.3 × 10⁻⁸ S cm⁻¹ and the I–V characteristic curves indicate a semiconducting nature with a signature of negative differential resistance.