Bi-component hydrogel of perylene-3, 4, 9, 10-tetracarboxylic potassium salt and L-tyrosine

Abstract

Potassium perylene-3,4,9,10-tetracarboxylate (P) and L-tyrosine (T) produces supramolecular PT complexes viz. PT11, PT12, PT13 and PT14 where the numbers indicate respective molar ratios. PT11 does not produce a hydrogel but the other three produce hydrogels with a minimum gelation concentration of 1.30% (w/v). All PT gels exhibit a fibrillar morphology and the gel melting temperature follows the order PT14 > PT13 > PT12. The frequency independent G' (G' > G'') for PT12, PT13 and PT14 systems characterize them as a gel and the critical yield stress values are 6.0, 3.18 and 0.76 Pa for PT14, PT13 and PT12, respectively. The presence of H-bonding and electrostatic interactions in PT complexes is evident from the FTIR spectra. NMR spectra suggest p-p stacking in both gels and in the PT11 complex, however, there is less p-stacking in the latter. The red shift of the absorption peaks of PT gels compared to that of P is attributed to the J-aggregate formation. The emission peaks also show red shifts and the emission intensity increases significantly. The average life time value decreases in the gels. With increasing temperature, PL-intensity gradually decreases due to the de-stacking of the J-aggregates but the emission peak position shows a step like increase due to batch-wise slipping of PT motifs from J-aggregates.