Efficient Enhancement of the Visible-Light Absorption of Cyclometalated Ir(III) Complexes Triplet Photosensitizers with Bodipy and Applications in Photooxidation and Triplet Triplet Annihilation Upconversion

Overview

Title: 

Efficient Enhancement of the Visible-Light Absorption of Cyclometalated Ir(III) Complexes Triplet Photosensitizers with Bodipy and Applications in Photooxidation and Triplet Triplet Annihilation Upconversion

Abstract: 

We report molecular designing strategies to enhance the effective visible light absorption of cyclometalated Ir(III) complexes. Cationic cyclometalated Ir(III) complexes were prepared in which boron-dipyrromethene (Bodipy) units were attached to the 2,2'-bipyridine (lapy) ligand via -C C- bonds at either the meso-phenyl (Ir-2) or 2 position of the pi core of Bodipy (Ir-3). For the first time the effect of pi conjugating (Ir-3) or tethering (Ir-2) of a light-harvesting chromophore to the coordination center on the photophysical properties was compared in detail. Ir(ppy)(2)(bpy) (Ir-1; ppy = 2-phenylpyridine) was used as model complex, which gives the typical weak absorption in visible range (epsilon < 4790 M-1 cm(-1) in region > 400 nm). Ir-2 and Ir-3 showed much stronger absorption in the visible range (epsilon = 71 400 M-1 cm(-1) at 499 nm and 83 000 M-1 cm(-1) at 527 nm, respectively). Room temperature phosphorescence was only observed for Ir-1 (lambda(em) = 590 nm) and Ir-3 (lambda(em) = 742 nm). Ir-3 gives RT phosphorescence of the Bodipy unit On the basis of the 77 K emission spectra, nanosecond transient absorption spectra, and spin density analysis, we proposed that Bodipy-localized long-lived triplet excited states were populated for Ir-2 (tau(T) = 231 mu s) and Ir-3 (87.2 mu s). Ir-1 gives a much shorter triplet state lifetime (0.35 mu s). Complexes were used as singlet oxygen (O-1(2)) photosensitizers in photooxidation. The O-1(2) quantum yield of Ir-3 (Phi(Delta) = 0.97) is ca. 2-fold of Ir-2 (Phi(Delta) = 0.52). Complexes were also used as triplet photosensitizer for TTA upconversion; upconversion quantum yields of 1.2% and 2.8% were observed for Ir-2 and Ir-3, respectively. Our results proved that the strong absorption of visible light of Ir-2 failed to enhance production of a triplet excited state. These results are useful for designing transition metal complexes that show effective strong visible light absorption and long-lived triplet excited states, which can be used as ideal triplet photosensitizers in photocatalysis and TTA upconversion.

Authors: 

Jifu Sun, Fangfang Zhong, Xiuyu Yi, Jianzhang Zhao

DOI: 

Journal: 

Inorganic Chemistry

Year: 

2013

Menu