Synthesis, photophysical, and photochemical properties of functional molecules based on a novel zinc(II) phthalocyanine-1,8-naphthalimide skeleton

Designing multifunctional photosensitizers with high efficiency has been significant in the molecular engineering field. In this work, we designed a novel molecular skeleton with a bi-chromophore, in which four 4-substituted-1,8-naphthalimide fluorophores were introduced as energy pumps to the zinc(II) phthalocyanine photosensitive group. Four peripherally symmetrical 4-NH-substituted-1,8-naphthalimide functionalized zinc(II) phthalocyanine molecules (NAZP1, NAZP2, NAZP3, NAZP4) were synthesized and characterized. The photophysical and photochemical properties of the molecules were investigated. The novel molecules showed dual-channel absorption and emission features of both chromophores. The fluorescence resonance energy transfer (FRET) process from 1,8-naphthalimide to zinc(II) phthalocyanine was verified by the spectral overlap and theoretical calculations. NAZP1 had higher FRET efficiency than the other three molecules. The singlet oxygen quantum yields of NAZP1, NAZP2, NAZP3, and NAZP4 in DMF were 0.84, 0.60, 0.68, and 0.73 respectively, being higher than the unsubstituted ZnPc. The introduction of four 1,8-naphthalimide energy pumps greatly improved the photophysical and photochemical properties of zinc(II) phthalocyanine, being hopeful in developing high-performance photosensitizers.