Dual antioxidant-oxidant activity, optical properties and thermal stability of 1,5-diaminonaphthalene

Abstract

1,5-Diaminonaphthalene (DAN) is a small polyaromatic molecule known for its remarkable antioxidant properties. While its effective radical-scavenging activity under ambient conditions has been previously documented, this study unveils an equally compelling yet contrasting duality in the nature of this molecule. Indeed, DAN can also act as a photosensitizer under UV light irradiation, generating reactive singlet oxygen species, ¹O₂. We have studied the mechanisms underlying this dual behavior using a combination of characterization techniques, including FTIR, XRD, thermogravimetric analysis, UV–Vis spectroscopy, and electronic paramagnetic resonance. Without light, DAN efficiently neutralizes the 2,2-Diphenyl-1-picrylhydrazyl (DPPH^·) radicals used as probe molecules through hydrogen atom transfer and exhibits antioxidant properties. However, under UV-light irradiation, DAN nature shifts dramatically. The photo-stimulation enables the production of reactive singlet oxygen with significant oxidative response, as demonstrated by the test with the standard probe indocyanine green. This light-triggered transformation highlights the versatility of DAN, bridging its use as a radical scavenger and pro-oxidant. The findings pave the way for exploiting the dynamic redox properties of DAN in designing multifunctional nanomaterials where controlled oxidative and antioxidative responses are critical.