Femtosecond transient absorption studies of two novel energetic tetrazole derivatives

Excited-state dynamics of two novel energetic nitrogen-rich aryl-tetrazole molecules were investigated using femtosecond transient absorption spectroscopy. The internal conversion from Sn to S1 occurred in the 0.3–0.5 ps; vibrational relaxation within S1 states transpired in a 1.8–5 ps time scale and, subsequently, the intersystem crossing was observed with lifetimes of 7.8 ps and 129 ps. The nitro-substituted tetrazole demonstrated a faster decay with a weaker fluorescence compared to the amino-substituted derivative. We believe that the high nitrogen content in the former resulted in a possible more rapid nonradiative decay. © 202

Nonlinear optical studies of sodium borate glasses embedded with gold nanoparticles

Optical glasses possessing large third-order optical nonlinear susceptibility and fast response times are promising materials for the development of advanced nonlinear photonic devices. In this context, gold nanoparticle (NP)-doped borate glasses were synthesized via the melt-quench method. The nonlinear optical (NLO) properties of thus prepared glasses were investigated at different wavelengths (i.e., at 532 nm using nanosecond pulses, at 750 nm, 800 nm, and 850 nm wavelengths using femtosecond, MHz pulses). At 532 nm, open aperture (OA) Z-scan signatures of gold NP-doped borate glasses demonstrated reverse saturable absorption (RSA), attributed to mixed intra-band and interband transitions, while in the 750850 nm region, the OA Z-scan data revealed the presence of saturable absorption (SA), possibly due to intra-band transitions. The NLO coefficients were evaluated at all the spectral regions and further compared with some of the recently reported glasses. The magnitudes of obtained NLO coefficients clearly demonstrate that the investigated glasses are potential materials for photonic device applications

Non-critically phase-matched second harmonic generation and third order nonlinearity in organic crystal glucuronic acid gamma-lactone

The linear, second order, and third order nonlinear optical properties of glucuronic acid gamma-lactone single crystals were investigated. The optic axes and principal dielectric axes were identified through optical conoscopy and the principal refractive indices were obtained using the Brewster's angle method. Conic sections were observed which is perceived to be due to spontaneous non-collinear phase matching. The direction of collinear phase matching was determined and the d(eff) evaluated in this direction was 0.71 pm/V. Open and closed aperture Z-scan measurements with femtosecond pulses revealed high third order nonlinearity in the form of self-defocusing, two-photon absorption, as well as saturable absorption. Published by AIP Publishing

Ultrafast photophysical studies and femtosecond third-order nonlinear optical properties of a Soret-band excited zinc phthalocyanine

Herein, results from the investigation of ultrafast photophysical and third-order nonlinear optical properties of newly synthesized Zn phthalocyanine, namely [Zinc (II) 2,10,16,24tetrakis(2,6-dichloropyridin-3-yl) phthalocyanine, PyCl2PC] molecule are presented. The photophysical properties were studied using femtosecond transient absorption spectroscopy while the NLO properties were measured using the single beam Z-scan and degenerate four-wave mixing (DFWM) techniques. The transient absorption spectra were obtained at 400 nm photoexcitation and a white light continuum probed the corresponding dynamics from (440-780 nm) in the solution phase. The obtained transient absorption spectra were globally fitted using a kinetic model which yielded the different photophysical constants after photoexcitation such as (i) internal conversion from higher electronic excited state (Sn) to lower electronic state (S1) happening in 1 ps (ii) Vibrational relaxation (6.25 ps) occurring within the S1 states (III) Intersystem crossing (1.78 ns) (IV) relaxation from the triplet states to ground state (0.11 μs). Nonlinear absorption properties were measured at 800 nm wavelength utilizing ~70 fs, 1 kHz laser pulses in the solution phase. A large two-photon absorption coefficient (β) of ~8×10-13 cm/W was obtained and the corresponding cross-section was estimated to be 659 GM. Time-resolved degenerate four-wave-mixing measurements revealed a large magnitude and an ultrafast response of χ(3)

Plasmon Induced Ultrafast Excited State Interfacial Electron Dynamics of Tetrathiafulvalene Sensitizers

Silver (Ag) nanoparticle induced enhanced electron-injection and reduced chargerecombination dynamics in two thioalkyl substituted tetrathiafulvalene dye (G1 and G3)- sensitized mesoporous TiO2 layers have been investigated using femtosecond transient-absorption spectroscopy with 400 nm excitation

Ultrafast nonlinear optical properties and excited-state dynamics of Soret-band excited D-π-D porphyrins

Herein, we report results from our studies on the ultrafast nonlinear optical (NLO) properties and excited-state dynamics in three different porphyrin molecules designed in D-π-D fashion (phenothiazine-porphyrin-phenothiazine) and with two different central metal ions [Zn(II) and Cu(II)]. We have performed extensive target analysis of the femtosecond transient absorption data obtained conveying the true exited state/species spectra of each process with respective lifetimes along with microscopic rate constants of each excited state. The obtained life time values were in the range of 250–500 fs, 20–142 ps, 1.5–6.2 ns and 0.1–1.23 μs and have been associated from relaxation with the Sn, Hot S1 (to S1), S1, and T1 states. Furthermore, the third-order nonlinear (NLO) coefficients [two-photon absorption (TPA) and nonlinear refractive index (n2)] of CPPHT and ZPPHT exhibited superior values compared to HPPHT recorded with ~50 fs, 1 kHz repetition rate pulses at a wavelength of 800 nm. The magnitude of the TPA coefficients of these molecules was compared with some of the recently reported porphyrin moieties and were found to be superior. The time-resolved degenerate four-wave mixing (DFWM) measurements confirmed a large magnitude and an ultrafast response of the χ(3) in these molecules suggesting potential photonic and all-optical switching applications

Multistep Electron Injection Dynamics and Optical Nonlinearity Investigations of π-Extended Thioalkyl-Substituted Tetrathiafulvalene Sensitizers

A comprehensive investigation is presented on the photophysical and third-order nonlinear optical (NLO) properties of two thioalkyl-substituted tetrathiafulvalene molecules (referred here as G1 and G3) to understand their utility as photosensitizers for dye-sensitized solar cell (DSSC) and optoelectronic applications. Both steady-state and time-resolved (in the fs−ns time regime) absorption and photoluminescence (PL) spectroscopy techniques were employed to comprehend the excited-state properties of the molecules in solution as well as in thin films deposited on both quartz and mesoporous TiO2 layers. The spectroscopy measurements in solution and thin films deposited on quartz provided the excited-state properties of dye molecules. Time-resolved PL measurements at the dye−TiO2 interface provided initial evidence of electron injection by fast PL quenching decay dynamics for both the molecules. Detailed target analysis of the femtosecond transient absorption spectroscopy (TAS) data of the dye−TiO2 sample revealed a multistep ultrafast electron injection for both molecules with the fastest injection component being 374 and 314 fs for G1 and G3 molecules, respectively. The ultrafast NLO properties of G1 and G3 were studied using the Z-scan technique with 800 nm, ∼70 fs laser pulses. The open aperture measurements showed three-photon absorption with magnitudes of coefficients 4.7 × 10−5 cm3/GW2 and 5.2 × 10−5 cm3/GW2, and the closed aperture measurements provided second hyperpolarizability (γ) values of 3.5 × 10−31 esu and 4.2 × 10−31 esu for G1 and G3, respectively. Additionally, the onset of optical limiting was estimated to be 5.8 × 10−3 J/cm2 and 5.7 × 10−3 J/cm2 for G1 and G3 molecules, respectively

Ultrafast photophysical and nonlinear optical properties of novel free base and axially substituted phosphorus (V) corroles

The progression in synthetic procedures over the last two decades gave admittance to a wide variety of corroles for suitable potential applications such as photovoltaics, photonics, and bio-imaging. In this communication, we present results from our investigations of ultrafast photophysical processes and third-order nonlinear optical properties of newly synthesized donor-acceptor based free-base [(C6F5)3] and phosphorus [P-(OH)2(C6F5)3] corroles. The global analysis of the femtosecond transient absorption data based on the compartmental model revealed the corresponding time constants of several photophysical processes such as (a) internal conversion (τIC) in the 260–280 fs range (b) vibrational relaxation (τVR) in the 2.5-5 ps range and (c) nonradiative relaxation times (τnr) in the 4.15–7.6 ns range and finally (d) triplet lifetimes in the range of 25–50 μs. The two-photon absorption (TPA) cross-section measurements were performed using the femtosecond, kHz pulse Z-Scan technique at 600 nm and 800 nm and the retrieved TPA cross-section values were in the range of ~102 GM. Degenerate four-wave mixing measurements illustrated a large third-order nonlinear optical susceptibility χ(3) with a magnitude of 6.9 × 10−14 esu and instantaneous (sub-picosecond) response, suggesting a pure electronic contribution to the nonlinearity of these corroles. The discoveries from this study may help further to extend the capability of corroles as NLO materials for photonic applications

Ultrafast photophysical studies and femtosecond third-order nonlinear optical properties of a Soret-band excited zinc phthalocyanine

Herein, results from the investigation of ultrafast photophysical and third-order nonlinear optical properties of newly synthesized Zn phthalocyanine, namely [Zinc (II) 2,10,16,24tetrakis(2,6-dichloropyridin-3-yl) phthalocyanine, PyCl2PC] molecule are presented. The photophysical properties were studied using femtosecond transient absorption spectroscopy while the NLO properties were measured using the single beam Z-scan and degenerate four-wave mixing (DFWM) techniques. The transient absorption spectra were obtained at 400 nm photoexcitation and a white light continuum probed the corresponding dynamics from (440-780 nm) in the solution phase. The obtained transient absorption spectra were globally fitted using a kinetic model which yielded the different photophysical constants after photoexcitation such as (i) internal conversion from higher electronic excited state (Sn) to lower electronic state (S1) happening in 1 ps (ii) Vibrational relaxation (6.25 ps) occurring within the S1 states (III) Intersystem crossing (1.78 ns) (IV) relaxation from the triplet states to ground state (0.11 μs). Nonlinear absorption properties were measured at 800 nm wavelength utilizing ∼70 fs, 1 kHz laser pulses in the solution phase. A large two-photon absorption coefficient (β) of ∼8×10-13 cm/W was obtained and the corresponding cross-section was estimated to be 659 GM. Time-resolved degenerate four-wave-mixing measurements revealed a large magnitude and an ultrafast response of χ(3)

Cyclometalated Iridium(III) Complexes Containing 4,4′-π-Conjugated 2,2′-Bipyridine Derivatives as the Ancillary Ligands: Synthesis, Photophysics, and Computational Studies

This article demonstrates a series of cyclometalated Ir­(III) complexes of the type [Ir^III(C^N)₂­(N^N)]­(PF₆), where C^N is 2-phenylpyridine, and N^N corresponds to the 4,4′-π-conjugated 2,2′-bipyridine ancillary ligands. All these compounds were synthesized through splitting of the binuclear dichloro-bridged complex precursor, [Ir­(C^N)₂­(μ-Cl)]₂, with the appropriate bipyridine ligands followed by the anion exchange reaction. The linear and nonlinear absorption properties of the synthesized complexes were investigated. The absorption spectra of all the title complexes exhibit a broad structureless feature in the spectral region of 350–700 nm with two bands being well-resolved in most of the cases. The structures of all the compounds were modeled in dichloromethane using the density functional theory (DFT) algorithm. The nature of electronic transitions was further comprehended on the basis of time-dependent DFT analysis, which indicates that the origins of various bands are primarily due to intraligand charge transfer transitions along with mixed-metal and ligand-centered transitions. The synthesized compounds are found to be nonemissive at room temperature because of probable nonradiative deactivation pathways of the T₁ state that compete with the radiative (phosphorescence) decay modes. However, the frozen solutions of compounds <b>Ir­(MS 3)</b> and <b>Ir­(MS 5)</b> phosphoresce at the near-IR region, the other complexes remaining nonemissive up to 800 nm wavelength window. The two-photon absorption studies on the synthesized complexes reveal that values of the absorption cross-section are quite notable and lie in the range of 300–1000 GM in the picosecond case and 45–186 GM in the femtosecond case