Synthesis and photophysical properties of doubly β-to-β bridged cyclic Zn(II) porphyrin arrays

Abstract

A series of doubly β-to-β bridged cyclic Zn(II) porphyrin arrays were prepared by a stepwise Suzuki-Miyaura coupling reaction of borylated Zn(II) porphyrin with different bridge groups. The coupling of the building block of β,β'-diboryl Zn(II) porphyrin 1 with different bridges provided the doubly β-to-β carbazole-bridged Zn(II) porphyrin array 3, the fluorene-bridged Zn(II) porphyrin array 5, the fluorenone-bridged Zn(II) porphyrin array 7, and the three-carbazole-bridged Zn(II) porphyrin ring 8. The structural assignment of 3 was confirmed by the X-ray diffraction analysis, which revealed a highly symmetrical and remarkably bent syn-form structure. The incorporation of bridge units with different electronic effects results in different photophysical properties of the cyclic Zn(II) porphyrin arrays. Comprehensive photophysical studies demonstrate that the electron-withdrawing bridge fluorenone has the largest electronic interaction with the Zn(II) porphyrin unit among the series, thus resulting in the highest two-photon absorption cross-section values (σ((2))) of 6570±60 GM for 7. The present work provides a new strategy for developing porphyrin-based optical materials.