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Monocationic Iridium(III) Complexes with Far‐Red Charge‐Transfer Absorption and Near‐IR Emission: Synthesis, Photophysics, and Reverse Saturable Absorption
Author(s) -
Liu Bingqing,
Lystrom Levi,
Cameron Colin G.,
Kilina Svetlana,
McFarland Sherri A.,
Sun Wenfang
Publication year - 2019
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201900156
Subject(s) - chemistry , iridium , absorption (acoustics) , excited state , singlet state , ultrafast laser spectroscopy , photochemistry , ligand (biochemistry) , absorption spectroscopy , phosphorescence , absorption band , triplet state , molar absorptivity , ground state , diimine , fluorescence , spectroscopy , molecule , atomic physics , catalysis , organic chemistry , materials science , biochemistry , physics , receptor , quantum mechanics , optics , composite material
The synthesis, photophysics, and reverse saturable absorption (RSA) of three monocationic iridium(III) complexes ( Ir1 – Ir3 ) bearing diimine (N ^ N) ligand with different degrees of π‐conjugation are reported. Spectroscopic methods, including UV/Vis absorption, emission, and transient absorption spectroscopy, and density functional theory calculations were carried out to understand the nature of the singlet and triplet optical transitions and the influence of N ^ N ligand π‐conjugation on the photophysical properties of the complexes. All complexes possessed predominant ligand–centered, 1 π , π* absorption bands at 280–420 nm and weak charge‐transfer absorption bands at 420–610 nm for Ir1 , 420–680 nm for Ir2 , and 420–730 nm for Ir3 . The extended π ‐conjugation of the N ^ N ligand red–shifted the charge‐transfer absorption bands and increased the molar extinction coefficients of all of the absorption bands. All complexes were emissive in the far‐red to the near‐infrared regions, with the emission energies gradually decreasing when the π‐conjugation of the N ^ N ligand increased. However, the emission lifetime of Ir3 increased when its emitting state energy decreased. This was caused by the different nature of the T 1 state in Ir3 , which was the predominant N ^ N ligand–localized 3 π , π* state compared to the charge‐transfer T 1 states in Ir1 and Ir2 . The different parentage of the T 1 state in Ir3 also gave rise to a much broader and stronger triplet excited‐state absorption in the 420–800 nm regions. The varied ground‐state and triplet excited‐state absorption characteristics led to a different strength of the reverse saturable absorption (RSA) for ns laser pulses at 532 nm, with the RSA strength following the trend of Ir3 > Ir1 ≥ Ir2 . Complex Ir3 is particularly attractive for its potential as a broadband reverse saturable absorber in view of its broader ground‐ and excited‐state absorption in the regions of 420–730 nm and longer–lived triplet excited state.