Synthesis of zinc chlorin–spiropyran dyads and their self-aggregation properties

• Photochromic spiropyran was appended to self-aggregative chlorophyll derivatives.
• Spiropyran moiety in the chlorophyll derivatives reversibly isomerized by photoirradiation.
• Open form of spiropyran, merocyanine form, quenched fluorescence emission of the chlorophyll moiety.
• Self-aggregation properties of zinc 31-hydroxy-chlorins were affected by isomerization of spiropyran moiety.
• Photo-triggered reversible self-aggregation of zinc 31-methoxy-chlorin was observed.

A photochromic spiropyran moiety has been covalently linked to a self-aggregative zinc analog of chlorophyllous pigments. Semi-synthetic zinc chlorins possessing a 31-hydroxy- or 31-methoxy group were used as the chlorophyll model, and the spiropyran part was introduced at the 17-position of the chlorin macrocycle. The spiropyran moiety reversibly isomerized to its opened merocyanine form in the dyads. The photoisomerization induced drastic change in electric dipole moment of the side chain, and photoswitchable chlorophyll aggregation was found in the pigment conjugates.

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