Synthesis and self-aggregation of chlorophyll derivatives possessing a pyrazole ring at the C3 position

• The β-diketonate group connected with chlorin was reacted with hydrazines.
• C3-Pyrazolylated or pyrazolinylated chlorophyll derivatives were synthesized.
• The substituents on the heterocyclic ring affected the optical properties of chlorin.
• N-Unsubstituted pyrazole–zinc chlorin dimerized in nonpolar organic solvent.

Chlorophyll compounds possessing an N-(un)substituted pyrazole ring at the C3 position were synthesized by the reaction of chlorophyll-a derivative having a trifluoromethyl-β-diketonate group with (substituted) hydrazines in 2,2,2-trifluoroethanol through the pyrazoline ring. The substituents on the C3-heterocyclic 5-membered ring affected the electronic absorption and emission of the monomeric chlorin molecules. Vis, CD and 1H NMR spectra of the zinc chlorin bearing an N-unsubstituted pyrazole showed its dimerization in a nonpolar organic solvent.

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