Nanoencapsulation-Induced Second Harmonic Generation in Pillararene-Based Host-Guest Complex Cocrystals

The features of molecularly preferable centrosymmetric arrangements exclude organic nonlinear optical (NLO) materials for second harmonic generation (SHG) when used in the solid and crystalline states, which greatly limits their applications in optoelectronic devices. Herein, a pillar[5]arene (BrP5) is used as the macrocyclic host to encapsulate NLO molecules, 4-[4'-methoxystyryl]-1-methylpyridinium iodide (OM), 4-[2'-(5'-(dimethylamino)thiophen-2'-yl)vinyl]-1-methylpyridinium iodide (DAST), and 4-methoxy-β-nitrostyrene (MNS), to alter the solid-state packing of these NLO molecules and manipulate their centrosymmetric arrangements. BrP5 forms 2:1 host-guest complexes with OM and DAST, while it forms a 1:1 host-guest complex with MNS. Experimental results show that the pillar[5]arene and each of these three NLO guests form a nanocapsule architecture along with an overall centrosymmetric crystal structure. However, the random orientation of OM and DAST molecules inside the 2:1 host-guest complex nanocapsules breaks the local centrosymmetric arrangement of the NLO molecules, resulting in strong SHG. On the contrary, for BrP5⊃MNS, the MNS molecules inside the pillar[5]arene cavities are unable to break the centrosymmetry. They have only one determined orientation in the one-dimensional (1D) channels of BrP5, while other MNS molecules in adjacent channels have the opposite direction. The centrosymmetry of the dipolar chains is strictly maintained with the cancellation of nonlinear polarization, resulting in the quenching of SHG. Furthermore, an ultrasound-induced host-guest crystallization method is developed for the fast preparation of these host-guest composite materials with NLO activity. This work opens a new way to construct solid-state organic NLO materials, which have potential in high-power lasers, optical switches, and imaging applications.

Two-photon activated precision molecular photosensitizer targeting mitochondria

Mitochondria metabolism is an emergent target for the development of novel anticancer agents. It is amply recognized that strategies that allow for modulation of mitochondrial function in specific cell populations need to be developed for the therapeutic potential of mitochondria-targeting agents to become a reality in the clinic. In this work, we report dipolar and quadrupolar quinolizinium and benzimidazolium cations that show mitochondria targeting ability and localized light-induced mitochondria damage in live animal cells. Some of the dyes induce a very efficient disruption of mitochondrial potential and subsequent cell death under two-photon excitation in the Near-infrared (NIR) opening up possible applications of azonia/azolium aromatic heterocycles as precision photosensitizers. The dipolar compounds could be excited in the NIR due to a high two-photon brightness while exhibiting emission in the red part of the visible spectra (600-700 nm). Interaction with the mitochondria leads to an unexpected blue-shift of the emission of the far-red emitting compounds, which we assign to emission from the locally excited state. Interaction and possibly aggregation at the mitochondria prevents access to the intramolecular charge transfer state responsible for far-red emission.

Large-sized benzo[e]indolium salt single crystals with high optical nonlinearity

Two new benzo[e]indolium salts with highly efficient nonlinear optical performance and excellent crystal characteristics were synthesized.

A series of stilbazolium salts with A-π-A model and their third-order nonlinear optical response in the near-IR region

A series of water-soluble stilbazolium salts with A-π-A (A: Acceptor) model have been synthesized and fully characterized. The results obtained from absorption spectra and TD-DFT computational studies show that there is a relative strong intramolecular charge transfer (ICT) transition from pyridine unit to pyridine cation of the stilbazolium salts. Furthermore, it is found that the three stilbazolium salts (T1, T2, T3) show the strong two-photon absorption (2PA) response in the near-infrared (IR) region by Z-scan technique using femtosecond laser. And the stilbazolium salt T3 shows the largest two-photon absorption cross-section and third-order nonlinear optical (NLO) coefficient χ⁽³⁾ at 730nm, indicating the different terminal substituent group of the pyridinium plays a vital role in third-order NLO behavior.

Crystal growth, spectral, structural and optical studies of π-conjugated stilbazolium crystal: 4-bromobenzaldehyde-4'-N'-methylstilbazolium tosylate

Nonlinear optical (NLO) organic compound, 4-bromobenzaldehyde-4'-N'-methylstilbazolium tosylate was synthesized by reflux method. The formation of molecular complex was confirmed from (1)H NMR, FT-IR and FT-Raman spectral analyses. The single crystals were grown by slow evaporation solution growth method and the crystal structure and atomic packing of grown crystal was identified. The morphology and growth axis of grown crystal were determined. The crystal perfection was analyzed using high resolution X-ray diffraction study on (001) plane. Thermal stability, decomposition stages and melting point of the grown crystal were analyzed. The optical absorption coefficient (α) and energy band gap (E(g)) of the crystal were determined using UV-visible absorption studies. Second harmonic generation efficiency of the grown crystal was examined by Kurtz powder method with different particle size using 1064 nm laser. Laser induced damage threshold study was carried out for the grown crystal using Nd:YAG laser.

Synthesis, growth, crystal structure, spectral, thermal, mechanical and optical studies of stilbazolium derivative single crystal: 2-[2-(4-Diethylamino-phenyl)-vinyl]-1-methyl-pyridinium naphthalene-2-sulfonate (DESNS)

Single crystals of organic optical material, 2-[2-(4-Diethylamino-phenyl)-vinyl]-1-methyl-pyridinium naphthalene-2-sulfonate (DESNS) (15×10×9 mm(3)) were grown by a slow evaporation technique at room temperature using methanol-acetonitrile (1:1) mixed solvent. The molecular structure of the grown crystal was confirmed by single crystal X-ray diffraction studies, and it belongs to orthorhombic system with space group Pbca and the unit cell dimentions are a=11.5148(3) Å, b=15.4352(4) Å, c=27.2187(7) Å, Z=8. The crystallinity of the title crystals was confirmed from the powder XRD pattern. The presence of functional groups of the title crystal was confirmed from the FTIR spectral studies. The transparent range and cut off wavelength of the grown crystal was studied by the UV-Vis-NIR spectroscopic analysis. The mechanical properties and thermal behavior of the grown crystals were studied from Vickers microhardness test and TG/DTA.

Effect of additives on the large-size growth of 4-N,N-dimethylamino-4-N-methyl stilbazolium naphthalene-2-sulfonate (DSNS) single crystal: an efficient stilbazolium derivative NLO crystal with potential terahertz wave properties

We explored the growth of the highly nonlinear optical stilbazolium salt 4-N,N-dimethylamino-4-N-methyl stilbazolium naphthalene-2-sulfonate (DSNS) by a slow evaporation method.