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We performed a comprehensive study of the fast relaxation processes in three metal–organic Ir(III)-complexes in liquid solutions at room temperature in order to estimate their singlet–triplet conve...

The ultrafast response function of air is used to predict the pulsewidth dependence of 2, ff from our measurements in the near and mid-infrared. We predict 2, ff in the atmosphere, showing agreement with multiple literature measurements.

Here, we present our development of several experimental methods, which, when applied together, can provide a thorough characterization of the nonlinear refraction and absorption properties of materials. We focus mainly on time-resolved methods for studying both transient absorption and refraction that reveal molecular dynamics including excited-state absorption, singlet-triplet transfer, instantaneous electronic nonlinear refraction, and molecular reorientation. In particular, we will describe our recent studies of new materials including organometallic compounds and organic solvents such as Tetrachloroethylene (C2Cl4).

By exciting in both the Near-IR and Mid-IR and probing in the mid-IR, using the polarization-resolved Beam Deflection Technique, the bound electronic nonlinear refractive index of air is measured below the ionization threshold.

We use the ultrafast response function of air to predict the pulsewidth dependence of from measurements in the near and mid-infrared showing no dispersion. This allows predictions of the dependence of n nnnnn on altitude.

Linear steady-state and time-resolved spectroscopic properties, degenerate two-photon absorption (2PA) spectra, and photochemical stability of IrIII complexes TCQ[IrIII(ppz)2]n, (TCQ = tricycloquinazoline; ppz = 1-phenylpyrazole; n = 1 (1), n = 2 (2), and n = 3 (3)) are presented for liquid solutions. The analysis of the linear photophysical properties revealed the nature of the observed dual-component fluorescence–phosphorescence emission of 1–3 at room temperature. The values of 2PA cross sections were determined by open aperture Z-scans using a 1 kHz femtosecond laser system. The specific dependence of the 2PA efficiency on the number of ppz ligand units in 1–3 was determined. The quantum yields, Φph, for photochemical decomposition of TCQ[IrIII(ppz)2]n complexes were obtained for the first time using the absorption method [Corredor, C. C.; J. Photoch. Photobio. A 2006, 184, 105−112] with continuous wave laser irradiation, and the highest stability of Φph ≈ 4 × 10–6 was shown for 2 in toluene.

Comprehensive investigations of the linear and nonlinear optical properties of new Ir(III)-complexes [Ir(pbt)2(dbm)] (1), [Ir(pbt)2(dmac)] (2), and [Ir(pbt)2(minc)] (3) (pbt=2-phenylbenzothiazole; dbm=dibenzoyl methane; dmac=(1E,4Z,6E)-1,7-bis(4-(dimethylamino)phenyl)-5-hydroxyhepta-1,4,6-trien-3-one; minc=(1E,4Z,6E)-5-hydroxy-1,7-bis(1-methyl-1H-indol-3-yl)hepta-1,4,6-trien-3-one) are reported, including, photostability, two-photon absorption, and femtosecond transient absorption spectroscopy. The steady-state and time-resolved spectral properties of 1-3 revealed the electronic nature of the absorption bands, and photoluminescence emission of 2 and 3 shows both fluorescence and phosphorescence processes occurring simultaneously in liquid solution at room temperature. This unusual behavior of 2 and 3 can be explained by a dual-minimum potential surface of the excited electronic state resulting in two independent fluorescence and phosphorescence emission channels. The degenerate 2PA spectra of 1-3 were obt...

We used the polarization-resolved beam-deflection technique to separate the bound-electronic and molecular-rotational components of the transient nonlinear refraction (NLR) of ambient air in the Mid-infrared spectral range below the ionization threshold.

We use the polarization-sensitive, time-resolved Beam-Deflection technique to measure the nonlinear refraction of air, exciting in both the near and mid-IR and probing in the mid-IR. This gives us the first measurements for air using both excitation and probe in the mid-IR, and we find no dispersion of the bound-electronic nonlinear refractive index, n2,el(λ p ;λ e ), assuming, as has been shown earlier, that the nuclear rotational nonlinear refraction is nearly dispersionless. From these data, we can model the pulsewidth dependence of the effective nonlinear refractive index, n2,eff, i.e., as would be measured by a single beam. Interestingly, n2,eff is maximized for a pulsewidth of approximately 0.5 ps. The position of this maximum is nearly independent of pressure while its magnitude decreases with increasing pressure and temperature. From the measurements and modeling, we predict the nonlinear refraction in the atmosphere at different altitudes.

Cyanines with long conjugation length such as heptamethines are well known to have strong intramolecular and/or intermolecular interactions (i.e., ion paring and aggregation), which can affect their structures (i.e., symmetry breaking) and optical properties remarkably. In this paper, we report a covalently linked complementary cyanine complex of cationic and anionic heptamethines forming a highly polarizable zwitterionic cyanine–cyanine salt. The effect of the modification was studied in detail on both its electronic structure and its optical properties. This novel zwitterionic salt was found to exhibit a decreased ion-pairing-induced charge localization but with an increased electronic coupling between the excited states of the cyanine cation and the anion, resulting in unusual optical properties compared to closely related noncovalent complementary cyanine salts. The dual-arm Z-scan technique was used to study their third-order NLO properties, suggesting the electronic coupling in such preorganized zwi...

The nonlinear-optical properties of Iridium complexes including triplet yield and excited-state cross-sections was studied by steady-state time-resolved measurements using picosecond and femtosecond excitation at multiple wavelengths.

An investigation of Ir(III) complexes has been performed using double-pump probe (DPP) experiments to decouple the triplet quantum yield and triplet cross-section of these complexes. Both femtosecond and picosecond DPP measurements are presented.

The nonlinear refractive transients of organic solvents are measured. The response functions derived from liquids are used to predict pulsewidth dependent n2,eff . Comparisons are made between the second hyperpolarizabilities measured in liquid and gas phases.

Using the Beam Deflection Technique, the bound-electronic and nuclear reorientation contributions to the nonlinear refraction of air are separately measured in the mid-infrared as a function of time below the ionization threshold.