The photophysical properties of five methoxy-substituted 2-ethylhexylcinnamates were studied with experimental and theoretical methods. It was found that the fluorescence quantum yields varied strongly with the substitution pattern of the phenyl ring. A methoxy substitution at the meta position gave strong fluorescence, whereas the para substituted compounds were strongly quenched. This observation could be correlated to corresponding changes in the UV absorption spectra; the two lowest ππ* states were split for the meta-methoxy substituted cinnamate but almost degenerate for the para compound. Semi-empirical quantum mechanical calculations confirmed both the observed state order and the difference in the experimentally determined activation energies for non-radiative decay. This “meta-effect” was also preserved in the trimethoxy-substituted compounds, 2-ethylhexyl-2,4,5- and 2,4,6-trimethoxycinnamate, resulting in strong fluorescence and relatively high barrier for non-radiative decay in the former and weak fluorescence and relatively low barrier for non-radiative decay in the latter. The obtained information shows how the performance of the commercial sunscreen agent, 2-ethylhexyl-para-methoxycinnamate (OMC) might be improved.

In this work, hydrogels composed of hyaluronic dialdehyde (HAD) and amino-beta-cyclodextrin (ACD) incorporated with quaternary ammonium chitosan (HACC) were synthesized in situ via Schiff base reaction. The composition, morphology and mechanical properties were characterized using FTIR, ¹H-NMR, SEM and rheological testing. Hydrogels were prepared using different molecular weights of HAD. The results showed that a higher molecular weight of HAD has increased the swelling ratio up to 1715–1835% and enhanced the mechanical properties of hydrogels. Increasing the HAD content further improved stability and mechanical properties due to a higher degree of crosslinking. Quercetin (Que), was used as a hydrophobic drug to form an inclusion complex with ACD and was loaded in HAD-ACD-HACC hydrogels. Drug release, cytotoxicity and anti-inflammatory activity were investigated in vitro. The results indicated that quercetin release was higher in acidic media than in neutral solutions. Cellular assessment of quercetin loaded 100k-2 and 1M-2 hydrogels by scratch test encouraged the migration of human keratinocyte (HaCaT) cells. The anti-inflammatory activity of quercetin loaded 100k-2 hydrogel was improved compared to free quercetin against HaCaT cells. Thus, this quercetin-loaded hydrogel system offers a promising approach for controlled drug release, enhanced anti-inflammatory and wound healing activities in various biomedical applications.