Orthogonally aligned cyclic BODIPY arrays with long-lived triplet excited states as efficient heavy-atom-free photosensitizers.

Zhaoyang Zhu,Lijuan Jiao,Changjiang Yu,Zhongxin Li,Erhong Hao,Jianzhang Zhao,Qinghua Wu,Xue Zhang,Xing Guo

doi:10.1039/d1sc04893g

Zhaoyang Zhu, Lijuan Jiao + Show 7 more

Open Access

https://doi.org/10.1039/d1sc04893g

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Abstract

In photosensitizers, long triplet excited state lifetimes are key to their efficient electron transfer or energy transfer processes. Herein, we report a novel class of cyclic trimeric BODIPY arrays which were efficiently generated from easily accessible meso-mesityldipyrrinone and arylboronic acids in one pot. Arylboronic acid, for the first time, was used to provide a boron source for BODIPY derivatives. Due to the well-defined and orthogonally aligned BODIPY cores as verified by X-ray crystallography, these BODIPY arrays show strong exciton coupling effects and efficient intersystem crossings, and are novel heavy-atom-free photosensitizers with a long-lived triplet excited state (lifetime up to 257.5 μs) and good reactive oxygen species generation efficiency (up to 0.72) contributed by both 1O2 and O2−˙ under light irradiation.

Highlights

Chromophore arrays with well-de ned architectures possess unique photophysical properties and have attracted wide research interest in a variety of research elds.[1]
Inspired by our recent synthesis of boron-functionalized BODIPYs through organotri uoroborate salts,[20] we rationalized that arylboronic acids may be able to complex with a-hydroxydipyrrin and undergo further condensation to generate novel cyclic BODIPYs with B–O linkages (Fig. 1c)
We chose its analogue, meso-mesityldipyrrinone 2, as the starting material, which was smoothly generated as yellow powder in 66% yield within one step from the acid-catalyzed hydrolysis of readily available 1,9-dichlorodipyrrin 121 in DMF at room temperature (Scheme 1)

Summary

Introduction

Chromophore arrays with well-de ned architectures possess unique photophysical properties and have attracted wide research interest in a variety of research elds.[1]. These reported cyclic BODIPY arrays typically showed strong excitonic coupling of the singlet excited state due to their closely packed structures.[11,12,13,14,15,16,17] such systems with ne-tuned triplet excited states have not been developed. We report a series of calixarene-like cyclic trimeric BODIPY arrays based on the direct condensation of mesomesityldipyrrinones with arylboronic acids, and they show efficient ISC due to the orthogonally aligned BODIPY cores, good singlet oxygen generation efficiency and long-lived triplet excited states (Fig. 1c).

Results

Conclusion