Metal-Free Electrocatalytic Synthesis of Fused Azabicycles from N-Allyl Enamine Carboxylates

An electrocatalytic approach to access structurally significant azabicyclic scaffolds from N-allyl enamine carboxylates is illustrated. This metal-free method functions exclusively with a catalytic amount of iodide, strategically employed to electrochemically generate a reactive hypervalent iodine species, which facilitates the cascade bicyclization processes with enhanced precision and efficiency. Excellent functional group compatibility was observed, enabling the synthesis of a series of azabicycle derivatives. Detailed mechanistic and electrochemical studies enhance the comprehension of the reaction sequence.

Solvatochromism in highly luminescent environmental friendly carbon quantum dots for sensing applications: Conversion of bio-waste into bio-asset

Recently studies on synthesis and fluorescence based sensing in biocompatible carbon quantum dots (CQDs) have become a widely spoken topic of research due to the several advantageous properties of CQDs in compared to semiconductor quantum dots. In this work, we have reported the rarely reported solvatochromism along-with a high photoluminescence (PL) quantum yield (PLQY) of 22%. Samples have been synthesized by using a simple process of hydrothermal carbonization of a naturally occurring bio-waste i.e. Aegle marmelos leaves powder. The linear absorption and PL emission characteristics of CQDs have been studied in different solvent environments to explore the origin of the observed excitation dependent PL emissions characteristics of the sample. The interesting solvatochromic PL (SPL) behavior of CQDs are observed at an excitation wavelength of 325nm by dispersing them in different polar protic and aprotic solvents, which suggest their possible applications as a replacement of solvatochromic dye molecules for sensing applications. Different polarity functions and molecular-microscopic solvent polarity parameter (E_T^N) are used to calculate the change in dipole moment (Δδ) of the solute-solvent system and the origin of SPL in CQDs has been explained. The SPL behavior of CQDs has been utilized for fluorescence sensing of organic liquids (Ethanol and Tetrahydrofuran) in water. Whereas, the photo-induced electron transfer mediated quenching in PL of aqueous dispersion of CQDs has led to development of "turn off" fluorescence Fe³⁺ ion sensor with a detection limit of 0.12μM. Therefore, this work may open a new avenue of conversion of a bio-waste into a fluorescent bio-asset.

Continuous wave random lasing in naturally occurring biocompatible pigments and reduction of lasing threshold using triangular silver nanostructures as scattering media

Random lasers have enormous applications in several fields including speckle-free imaging and bio-imaging. Thus, recently, random laser (RL) generation (mostly under pulsed operation) has been demonstrated in several commercial organic dyes with high photoluminescence quantum yields (PLQY). Although some commercial organic dyes have high PLQYs, these have several limitations; particularly, these dyes are not bio-compatible and thus cannot be used in in vivo bio-imaging. In this study, rarely reported bio-inspired continuous-wave (CW) RL generation has been demonstrated at ca. 674 nm, pumped by a low power He-Ne laser, in naturally occurring pigments of Hibiscus rosa-sinensis leaves extract (HRLe). The lasing threshold was reduced by ∼2.4 times from 40.7 W cm^-2 (without scatterer) to 16.8 W cm^-2 using anisotropic triangular nanostructures of silver (TNS) as a scatterer with a typical number density of 8 × 10¹⁵ nos. per ml. Unprecedentedly, further RL generation at ca. 691.7 nm with spectrally narrowed emission modes with a line-width of ca. 1 nm along with a very low lasing threshold of 15 W cm^-2 has been demonstrated in a thin film of polyvinyl alcohol doped with methylene blue dye and TNS. This study will initiate a new era of development of bio-inspired RL for bio-photonics applications.

Measurement of large nonlinear refractive index of natural pigment extracted from Hibiscus rosa-sinensis leaves with a low power CW laser and by spatial self-phase modulation technique

We have reported here, for the first time, to the best of our knowledge, a high nonlinear refractive index (n_2e) of a natural pigment extracted from Hibiscus rosa-sinensis leaves by using spatial self-phase modulation technique (SSPM) with a low power CW He-Ne laser radiation at 632.8nm. It is found by UV-Vis absorption spectroscopic analysis that chlrophyll-a, chlrophyll-b and carotenoid are present in the pigment extract with 56%, 25% and 19%, respectively. The photoluminescence (PL) emission characteristics of the extracted samples have also been measured at room temperature as well as in the temperature range of 283-333K to investigate the effect of temperature on luminescent properties of the sample. By analyzing the SSPM experimental data, the nonlinear refractive index value of pigment extract has been determined to be 3.5×10^-5cm²/W. The large nonlinear refractive index has been assigned due to asymmetrical structure, molecular reorientation and thermally induced nonlinearity in the sample. The presented results might open new avenues for the green and economical technique of syntheses of organic dyes with such a large nonlinear optical property.

Template-free hydrothermal synthesis of amphibious fluorescent carbon nanorice towards anti-counterfeiting applications and unleashing its nonlinear optical properties

Bio-precursor based synthesis and counterfeiting applications of water-soluble, blue fluorescent carbon nanorice structures with good nonlinear optical properties are demonstrated.

Enhanced nonlinear optical properties of graphene oxide–silver nanocomposites measured by Z-scan technique

Enhanced (by ∼2.8) nonlinear optical property of GO–Ag nanocomposite has been reported by Z-scan technique at a visible wavelength of 532 nm. The synthesized GO–Ag nanocomposite is also displaying significant optical limiting effect.

Three-photon-induced four-photon absorption and nonlinear refraction in ZnO quantum dots

Three-photon-induced four-photon absorption via excited-state absorption and self-defocusing nonlinear refraction are reported for the first time, to our knowledge, in ZnO quantum dots with average sizes of 2.0+/-0.1 nm with 1064 nm radiation from a Q-switched Nd:YAG laser at a peak intensity of 2.5 GW/cm(2). By employing the three-level two-step model, the experimental results can be explained quite satisfactorily.

Efficient Generation of 200-230-nm Radiation in Beta Barium Borate by Noncollinear Sum-Frequency Mixing

Tunable ultraviolet radiation in the 200-230-nm region has been generated with beta barium borate crystals by type I sum-frequency mixing of the second harmonic with the fundamental beam from a dye laser pumped by the second harmonic of the same Nd:YAG laser. A noncollinear phase-matching configuration has made it possible to realize conversion efficiency of 21% at 208.3 nm with input power densities as low as 28 MW/cm(2) for the fundamental and 2.4 MW/cm(2) for its second-harmonic radiation. The absorption characteristic of a standard DNA sample has been studied with the generated tunable ultraviolet source, revealing additional features compared with those obtained with a spectrophotometer.

Generation of tunable 187.9-196-nm radiation in beta-BaB(2)O(4): errata

In Ref. 1, the first full sentence in the right-hand column of p. 1608 should read as: 'Although BBO is phase matchable down to 187 nm and shorter in this configuration without a very large (2-4 degrees ) change in theta (and hence in d(eff)), and B2 is also suitable to accommodate the phase matching, tunability below 187.9 nm becomes limited by the exponential increase in crystal absorption.'

Generation of tunable 187.9-196-nm radiation in beta-Ba(2)BO(4)

Tunable 187.9-196-nm vacuum-ultraviolet radiation was generated at room temperature in a beta barium borate crystal by sum-frequency mixing of Nd:YAG laser radiation and the second harmonic of a dye laser pumped by the second harmonic of the same Nd:YAG laser. By use of the advantageous noncollinear phase-matching configuration, a peak power of 1.3 kW was obtained at 194 nm with input power densities as low as 79MW/cm(2) for 1064-nm and 0.65MW/cm(2) for 237.3-nm radiation.