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To explore the photophysical properties of coordination compounds with enhanced two-photon absorption, two novel six-coordinated metal complexes (ML2, M = Cd(ii), Zn(ii)) from carbazole β-diketone ligand (HL = 4,4,4-trifluoro-1-(9-butylcarbazole-3-yl)-1,3-butanedione) were prepared and fully characterized. Their crystal structures were determined by X-ray diffraction analysis. Both variable temperature (1)H NMR spectra and MALDI-TOF mass spectrometry proved that the coordination compounds exhibit good stability in solution. The results of time-dependent density functional theory (TD-DFT) calculations indicated that the complexation of the ligands with metal ion extends the electronic delocalization in the coordination compounds, leading to enhanced two-photon absorption. The photophysical properties for the coordination compounds were identified relying on both experimentally and theoretically studies. Finally, confocal microscopy and two-photon microscopy fluorescent imaging of HepG2 cells labeled with the Zn(ii) complexe revealed its potential applications as a biological fluorescent probe.

Response theory is used to investigate one- and two-photon absorption (TPA) as well as the emission properties of a series of potential zinc ion and pH sensitive materials containing 2-(2′-hydroxyphenyl)benzoxazole (HPBO) end groups. Special emphasis is placed on the evolution of their optical properties upon combining with zinc ions or deprotonation. Our calculated results indicate that upon combining with zinc ions or deprotonation, these HPBO derivatives show drastic changes in their one-photon absorption (OPA), emission, and TPA properties. Moreover, the mechanisms of the probes are analyzed and found to be an intramolecular charge transfer. These compounds are thus proved to be excellent candidates for two-photon fluorescent zinc and pH probes.

The optical limiting properties of a series of peripherally substituted phthalocyanines with different central metals and axial chloride ligand for nanosecond pulses have been studied by solving numerically the two-dimensional paraxial field equation together with the rate equations using the Crank-Nicholson method. It is shown that all of these compounds exhibit good optical limiting behaviour, and phthalocyanines with heavier central metals have better optical limiting performance due to the faster intersystem crossing caused by the enhanced spin-orbit coupling. The major mechanism of optical limiting for long pulses is the sequential (singlet-singlet)×(triplet-triplet) nonlinear absorption. Dynamics of populations is characterized mainly by the effective transfer time of the population from the ground state to the lowest triplet state. The long lifetime of the triplet state is important but not determinant. In addition, the performance of optical limiting strongly depends on the thickness and concentration of the absorber.

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