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Second-order molecular hyperpolarizabilities (γ) of four tetraphenylchlorin derivatives were measured by the Z-scan technique at 784 nm in the off-resonant region and the enhancement in the hyperpolarizabilities of these derivatives in comparison to the regular porphyrins with the same external side-groups is explained on the basis of the difference in their Q-band oscillator strengths.

A novel dmit^2- complex: [(C₂H₅)₄N][Co(dmit)²], abbreviated as EtCo, was synthesized and its third-order optical nonlinearities were characterized by Z-scan technique at the wavelength of 1064 nm with laser duration of 40 ps. Z-scan curves revealed a negative nonlinear refraction at 1064 nm and a positive absorption was observed. The nonlinear refraction coefficient n₂, the nonlinear absorption coefficient β and the molecular second hyperpolarizability γ have been determined to be as large as 9.51×10^-19m²/W, 2.19×10^-12 m/W and 5.41×10^-31 esu respectively, suggesting that this material has potential applications in optical limiting.

A novel dmit^2- complex: [C₇H₇(C₂H₅)₃N][Ni(dmit)₂], abbreviated as BTEANDT, was synthesized and its third-order nonlinear optical properties were investigated by Z-scan technique at the wavelength of 1064 nm with laser duration of 20 ps. A self-focusing effect and a saturable absorption were observed. The nonlinear refraction coefficient n₂ and the nonlinear absorption coefficient β have been found to be 7.311 × 10^-18m²/W and -6.064 cm/GW when I₀=3.025 GW/cm². The intensity dependence curve of β was also studied and the result reveals that β is proportional to I₀. We explained the result with the theory of absorption cross-section.

Third-order optical nonlinearities of three highly-substituted phthalocyanines (Pcs) containing central metal atom VO, Al, and Cu were investigated under resonant conditions by femtosecond degenerate four-wave mixing. The dynamics of the nonlinear response was found to be strongly dependent on the nature of the central metal atom and molecular stacking form. The electronic molecular hyperpolarizability of the Pcs was evaluated and compared with their structure-related analogues. The electronic third-order susceptibilities of the solid films containing the Pcs were determined to be in the range of 10^-10 to 10^-9 esu. We attempt to give structure-property relationships in these macrocyclic compounds.

To provide an insight into the optical limiting (OL) behavior of a series of 3 metallated 1,4,8,11,15,18,22,25-octaalkylphthalocyanines; the third-order nonlinear optical (NLO) properties, one-photon absorption (OPA) and two-photon absorption (TPA) characterizations have been theoretically investigated by means of AM1, ZINDO and configuration interaction (CI) methods. The highest values for the TPA cross-section (δ(ω)) are exhibited by derivatives metallated with indium and lead. It is also seen that the nickel-metallated compound might be a passive optical limiter of the series, indicating the weakest δ(ω) and second hyperpolarizability (γ). Our calculated results are in good agreement with the previous experimental observations on the examined molecules.

A five-coordinate chloroiron(III) complex has been synthesized and characterized by X-ray diffraction analysis and UV-Vis spectroscopy. The maximum one-photon absorption (OPA) wavelengths recorded by both linear optical measurements and quantum mechanical computations using the configuration interaction (CI) method are estimated to be shorter than 400 nm in the UV region, showing good optical transparency to visible light. To investigate the microscopic third-order nonlinear optical (NLO) behavior of the title compound, we have computed both dispersion-free (static) and also frequency-dependent (dynamic) linear polarizabilities (α) and second hyperpolarizabilities (γ) at λ = 825–1125 nm and 1050–1600 nm wavelength areas using the time-dependent Hartree–Fock (TDHF) method. The ab-initio calculation results with non-zero values on (hyper)polarizabilities indicate that the synthesized molecule might possess microscopic third-order NLO phenomena.

N,N′-bis(5-bromosalicylidene)propane-1,2-diamine-O,O′,N,N′)-manganese(III) chloride transition metal complex has been synthesized and characterized by elemental analysis and UV-vis spectroscopy. Its crystal structure has been determined using X-ray diffraction analysis. To provide an insight into the optical limiting (OL) behavior of the title compound, the third-order nonlinear optical (NLO) properties, one-photon absorption (OPA) and two-photon absorption (TPA) characterizations have been theoretically investigated by means of the time-dependent Hartree–Fock (TDHF), AM1 and configuration interaction (CI) methods, respectively. According to ab initio calculation results, the examined molecule exhibits second hyperpolarizabilities (γ) with non-zero values at the positions of TPA peaks, implying microscopic third-order optical nonlinearity. The maximum OPA wavelengths recorded by linear optical experiment and quantum mechanical computations are estimated in the UV region to be shorter than 400 nm, showing good optical transparency to the visible light. The TPA cross-sections (δ(ω)) at values indicate that the synthesized compound might possess OL phenomena, which are in accord with the experimental observations on the manganese complexes in the literature.

The third-order optical nonlinearities of three planar transition metal (Ni, Cu and Pd) compounds with rigid quadridentate Schiff base derived from S-benzyl dithiocarbazate, were investigated systematically by Z-scan technique with picosecond laser pulses at 1064 nm. The three compounds exhibit both strong two-photon absorption and effective self-focusing performance. Due to the heavy atom effect, the second hyperpolarizability of PdZ molecule (〈γ〉 = 1.2 × 10^-29 esu) was found to be the highest compared to that of the other two molecules. The optical limiting properties were also measured, and the results suggest that PdZ may be a promising candidate for the application to optical limiting in the near-infrared region.

Third-order nonlinear optical properties of tetra-phenyl porphyrin (H${}_{\mathrm{\text{2}}}$TPP) derivatives viz., H${}_{\mathrm{\text{2}}}$TPP(OH)${}_{\mathrm{\text{4}}}$ and Zn(II)TPP doped in boric acid glass thin films were measured using single beam Z-scan and forward degenerate four-wave mixing (DFWM) techniques. Excited state lifetimes and absorption cross-sections were estimated from these experiments. Thickness of the porphyrin doped sandwich glass films were determined using DFWM technique for the first time. The values of nonlinear refractive index ($n_2$) obtained for these systems are are found to be sensitive to the nature of substituents in porphyrin molecule. These results are interpreted in terms of delocalized $\pi$ electrons contributing to the third-order optical nonlinearity.

Films with alternating layers containing anionic tetracarboxylic copper phthalocyanine [CuPc(COONa)₄] and cationic polydiallydimethylammonium chloride (PDDA) were fabricated by electrostatic self-assembled layer-by-layer (LBL) technique. The delicate structure of the film was characterized by a series of techniques. The third-order nonlinear optical properties of the film were measured by the Z-scan technique with laser duration of 4 ns and 21 ps at the wavelength of 532 nm. The film exhibited excellent nonlinear absorption and self-focusing effect. The second-order molecular hyperpolarizability γ value of the film was much larger than that of CuPc(COONa)₄ aqueous solution under the irradiation of whether ns or ps pulses. A series of damage experiments of the film for the intense laser pulses were conducted to prove the reliability of the experimental results under the conditions.

New inorganic-organic transparent composite films of the formula (Zn${}_{\mathrm{\text{2}}}$Al-LDH/ZnTPPS)${}_{\mathrm{\text{n}}}$ were fabricated using exfoliated cationic Zn${}_{\mathrm{\text{2}}}$Al layered double hydroxide (Zn${}_{\mathrm{\text{2}}}$Al-LDH) nanosheets and anionic meso-tertra(4-sulfophenyl) zinc porphyrin (ZnTPPS) through an electrostatic layerbylayer self-assembly method. The resulting composite films were characterized by UV-vis spectroscopy (UV-vis) scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results showed that the films have relatively smooth and orderly surfaces, with the large ring plane of the porphyrin molecules vertically aligned LDH nanosheets and can grow in a nearly linear fashion with increasing the deposition cycles. Z-scan measurements, which were conducted under laser irradiation at a wavelength of 532 nm pulse width of 6 ns, repetition rate of 10 Hz and light intensity at focus $E$ of 10 $\mu$J, revealed that the composite films have notable saturation absorption (cf., ZnTPPS in solution shows reverse saturation) and optical nonlinear self-defocusing behavior with the nonlinear optical absorption coefficient $\beta$ refractive index $n_{\mathrm{\text{2}}}$, and third-order NLO susceptibility ${\chi }^{\mathrm{\text{(3)}}}$ of the films increasing with the increase in number of layers of films (${\chi }^{\mathrm{\text{(3)}}}$ value is up to 7.86 × 10${}^{\mathrm{\text{-11}}}$ esu when $n=$ 40), implying the NLO responses could be modified by fine tuning the thickness of composite films.