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Effects of Varying the Benzannulation Site and π Conjugation of the Cyclometalating Ligand on the Photophysics and Reverse Saturable Absorption of Monocationic Iridium(III) Complexes
摘要： A series of monocationic iridium(III) complexes, [Ir(C^N)2(pqu)]+PF6? [pqu = 2-(pyridin-2-yl)quinoline, C^N = 2-phenylquinoline (1), 3-phenylisoquinoline (2), 1-phenylisoquinoline (3), benzo[h]quinoline (4), 2-(pyridin-2-yl)naphthalene (5), 1-(pyridin-2-yl)naphthalene (6), 2-(phenanthren-9-yl)pyridine (7), 2-phenylbenzo[g]quinoline (8), 2-(naphthalen-2-yl)quinoline (9), and 2-(naphthalen-2-yl)benzo[g]quinoline (10)], were synthesized in this work. These complexes bear C^N ligands with varied degrees of π conjugation and sites of benzannulation, allowing for elucidation of the effects of the benzannulation site at the C^N ligand on the photophysics of the complexes. Ultraviolet?visible (UV?vis) absorption and emission of the complexes were systematically investigated via spectroscopic techniques and time-dependent density functional theory calculations. Their triplet excited-state absorption and reverse saturable absorption (RSA) were studied by nanosecond transient absorption (TA) spectroscopy and nonlinear transmission techniques. The fusion of phenyl ring(s) to the phenyl ring or the 4 and 5 positions of the pyridyl ring of the C^N ligand resulted in red-shifted UV?vis absorption and emission spectra in complexes 2, 5?7, 9, and 10 compared to those of the parent complex 0, while their triplet lifetimes and emission quantum yields were significantly reduced. In contrast, the fusion of one phenyl ring to the other sites of the pyridyl group of the C^N ligand showed an insignificant impact on the energies of the lowest singlet (S1) and triplet (T1) excited states in complexes 1, 3, and 4 but noticeably affected their TA spectral features. The fusion of the naphthyl group to the 5 and 6 and positions at the pyridyl ring did not influence the S1 energy of complex 8 but altered the nature of the T1 states in 8 and 10 by switching them to the benzo[g]quinoline-localized 3π,π* state, which resulted in completely different emission and TA spectra in these two complexes. The site-dependent variations of the ground- and excited-state absorption induced strong but varied RSA from these complexes for 4.1-ns laser pulses at 532 nm, with the RSA strength decreasing in the trend of 3 > 7 ≈ 4 ≈ 9 ≈ 6 > 8 ≈ 1 ≈ 2 ≈ 5 > 10.
关键词： iridium(III) complexes,time-dependent density functional theory,spectroscopic techniques,photophysics,reverse saturable absorption,benzannulation
更新于2025-09-04 15:30:14
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Time-domain dynamics of reverse saturable absorbers with application to plasmon-enhanced optical limiters
摘要： An advanced full-wave time-domain numerical model for reverse saturable absorption (RSA) is presented and verified. Rate equations describing atomic relaxations and excitation dynamics are coupled to the Maxwell equations by using a Lorentzian oscillator, which models the kinetics-dependent light–matter interactions. The presented novel technique provides a versatile multiphysics framework for designing complex structures and integrating diverse material models that were not previously possible. The multiphysics framework allows capturing the behavior of the RSA materials embedded in artificial photonic nanostructures that cannot be analyzed with established techniques such as the Beer–Lambert law. To showcase the importance of the full-wave RSA analysis coupled to carrier kinetics, we analyze two plasmon-enhanced optical limiters: a metal grating and a Fabry–Perot cavity-like structure where we decrease the unenhanced limiter threshold by a factor of 3 and 13, respectively. This is a promising approach for developing RSA devices operating at reduced illumination levels and thereby significantly expanding their area of applicability to areas such as protective eyewear and automatically dimmed windows. By exploring the dynamic behavior of a given RSA system, this framework will provide critical insights into the design of transformative photonic devices and their complementary optical characterization, and serve as an invaluable utility for guiding the development of synthetic absorbing materials. We believe that our multiphysics models are crucial enabling tools that lay a necessary foundation for the numerical machinery required for the realization and optimization of optical limiting and all-optical switching systems.
关键词： rate equations,nonlinear plasmonics,multilevel system,optical limiters,reverse saturable absorption
更新于2025-09-04 15:30:14