Photochemical Hydrogen Storage with Hexaazatrinaphthylene (HATN

TL;DR

This study demonstrates that hexaazatrinaphthylene (HATN) can photochemically extract hydrogen from alcohols under violet light, revealing potential for hydrogen storage with specific solvent dependencies and detailed mechanistic insights.

Contribution

It provides the first experimental evidence of HATN's ability to photochemically hydrogenate in alcohols, supported by theoretical analysis of the hydrogen transfer mechanism.

Findings

Hydrogenation occurs in methanol, ethanol, and isopropanol but not in water.

Hydrogenated HATN shows characteristic optical, EPR, and NMR signals.

Mass spectrometry confirms di-hydrogenated and methoxy-modified HATN products.

Abstract

When irradiated with violet light, hexaazatrinaphthylene (HATN) extracts a hydrogen atom from an alcohol forming a long-living hydrogenated species. The apparent kinetic isotope effect for fluorescence decay time in deuterated methanol (1.56) indicates that the lowest singlet excited state of the molecule is a precursor for intermolecular hydrogen transfer. The photochemical hydrogenation occurs in several alcohols (methanol, ethanol, isopropanol) but not in water. Hydrogenated HATN can be detected optically by an absorption band at 1.78 eV as well as with EPR and NMR techniques. Mass spectroscopy of photoproducts reveal di-hydrogenated HATN structures along with methoxylated and methylated HATN molecules which are generated through the reaction with methoxy radicals (remnants from alcohol splitting). Experimental findings are consistent with the theoretical results which predicted that for the excited state of the HATN-solvent molecular complex, there exists a barrierless hydrogen transfer from methanol but a small barrier for the similar oxidation of water.