Nonlinear optical characterization of multinuclear iridium compounds containing tricycloquinazoline

Abstract

Nonlinear optical properties were characterized for a series of multinuclear iridium compounds of the form TCQ[Ir^III(ppz)₂]_n, where n=1, 2, or 3, TCQ is tricycloquinazoline, and ppz is 1-phenylpyrazole. Transient absorption (TA) spectroscopy indicated that the triplet metal-to-ligand charge transfer excited state was formed on a subpicosecond time scale and decayed back to the ground state on a microsecond time scale, consistent with precedents in the literature. TA bands were observed for all three compounds from 475 to 900 nm, implying the potential for reverse-saturable absorption (RSA) at those wavelengths. Z-scan measurements using picosecond and nanosecond pulses were obtained at 532 nm and confirmed the presence of RSA behavior for all three compounds. The triplet excited state cross sections and the RSA figure of merit were found to decrease with increasing n:1>2∼3.

Dual Emissive Multinuclear Iridium(III) Complexes in Solutions: Linear Photophysical Properties, Two-Photon Absorption Spectra, and Photostability

“…42 Here, we continue linear spectroscopic and nonlinear optical investigations of these new Ir III It should be mentioned that the synthesis of 1−3, their transient absorption spectra, triplet−triplet absorption cross sections, and nano-and picosecond Z-scan measurements at 532 nm were reported in the previous work. 16 The new set of data obtained here allows deeper understanding of the nature of the electronic structures of 1−3 and completes the experimental characterization of new TCQ[Ir III (ppz) 2 ] n complexes, which can be useful for practical applications in ■ EXPERIMENTAL SECTION Linear Spectroscopic and Photochemical Measurements. The chemical structures of the investigated compounds 1−3 are designed, synthesized at U.S. Army Research Laboratory, 16,43 and presented in Figure 1.…”

“…16 The new set of data obtained here allows deeper understanding of the nature of the electronic structures of 1−3 and completes the experimental characterization of new TCQ[Ir III (ppz) 2 ] n complexes, which can be useful for practical applications in ■ EXPERIMENTAL SECTION Linear Spectroscopic and Photochemical Measurements. The chemical structures of the investigated compounds 1−3 are designed, synthesized at U.S. Army Research Laboratory, 16,43 and presented in Figure 1. These complexes are not planar as each iridium center exhibits an octahedral geometry with respect to the attached ligands.…”

“…Investigations of the linear spectroscopic and nonlinear optical properties of metal–organic complexes is the subject of great interest for multiple practical applications, including organic electronics, − luminescence sensing, − bioimaging, − photodynamic therapy, − nonlinear optics, − etc. Iridium complexes with specific ligand compounds − are among the most promising structures for these applications because they exhibit extremely fast singlet–triplet conversion processes, − high intersystem crossing quantum yields, − and photochemical stability. , Ir complexes can exhibit efficient room-temperature phosphorescence, , good potential for color tunability, − and specific intramolecular charge-transfer processes, allowing noticeable enhancement in a broad variety of nonlinear optical interactions. , Ultrafast relaxation processes in the excited state of iridium compounds, including transient excited-state absorption kinetics, the rates of singlet–triplet conversion, and electronic structures of excited-state potential surfaces, were investigated for numerous molecular complexes, such as Ir­(ppy) 3 (ppy = 2-phenylpyridine), Ir­(DBQ) 2 (acac) (DBQ = dibenzo­[ f , h ]­quinoxaline; acac = acetylacetonate) and Ir­(MDQ) 2 (acac) (MDQ = 2-methyl-dibenzo­[ f , h ]­quinoxaline), bis-heteroleptic Ir complexes with ethynyltolyl, ethynylpyrene and ethynylperylene, Ir­(piq) 3 (piq = 1-phenylisoquinoline), etc.…”

Fast Triplet Population in Iridium(III) Complexes with Less than Unity Singlet to Triplet Quantum Yield

“…We assume that all lifetimes of the higher excited electronic states (S n and T n ) are short enough that their populations are negligible, and the excitation intensities are not depleted because of additional ESA processes at the excitation wavelength. In contrast to the previous standard 5-level model shown in Figure (see refs ,,, ), we introduce the possibility of internal conversion processes, (S′ → S 0 ) with rate K NR , which allows us to obtain higher quality fittings for the majority of the experimental results. While the 5-level model is capable of fitting DPP dynamics for a single pair of input energies (i.e., energies of the first and second pump pulses), the six-level model is capable of giving fits for multiple different pairs of input energies using the same set of material parameters.…”

“…Metal–organic iridium complexes have attracted wide attention due to their high potential for applications in organic light-emitting diode technologies, − photoluminescence (PL) sensing, − nonlinear optics, − photodynamic therapy, − bioimaging, − and others. , All of these applications involve the lowest triplet state of these molecules; therefore, it is useful to develop a thorough understanding of the triplet state properties of these molecules. A broad variety of the linear photophysical and nonlinear optical spectral properties of these metal–organic structures − is connected to the efficient spin–orbit coupling caused by the heavy Ir atom effect − and strong electronic interaction with organic ligands. − …”