Two-Photon-Responsive "TICT + AIE" Active Naphthyridine-BF2 Photoremovable Protecting Group: Application for Specific Staining and Killing of Cancer Cells.

The combined effects of twisted intramolecular charge transfer (TICT) and aggregation-induced emission (AIE) phenomena have demonstrated a significant influence on excited-state chemistry. These combined TICT and AIE features have been extensively utilized to enhance photodynamic and photothermal therapy. Herein, we demonstrated the synergistic capabilities of TICT and AIE phenomena in the design of the photoremovable protecting group (PRPG), namely, NMe2-Napy-BF2. This innovative PRPG incorporates TICT and AIE characteristics, resulting in four remarkable properties: (i) red-shifted absorption wavelength, (ii) strong near-infrared (NIR) emission, (iii) viscosity-sensitive emission property, and (iv) accelerated photorelease rate. Inspired by these intriguing attributes, we developed a nanodrug delivery system (nano-DDS) using our PRPG for cancer treatment. In vitro studies showed that our nano-DDS manifested effective cellular internalization, specific staining of cancer cells, high-resolution confocal imaging of cancerous cells in the NIR region, and controlled release of the anticancer drug chlorambucil upon exposure to light, leading to cancer cell eradication. Most notably, our nano-DDS exhibited a substantially increased two-photon (TP) absorption cross section (435 GM), exhibiting its potential for in vivo applications. This development holds promise for significant advancements in cancer treatment strategies.

Temporal Release of Cell Cycle Regulator α-Lipoic Acid: An NIR-Light (Two-Photon) Activatable Quinoxaline-Based Nano-Prodrug Delivery System.

The regulation of the cell cycle has recently opened up a new research perspective for cancer treatment. So far, no effort has been made for temporal control of cell cycles using a photocleavable linker. Presented herein is the first report of regulation of disrupted cell cycles through the temporal release of a well-known cell cycle regulator α-lipoic acid (ALA), enabled by a newly designed NIR-active quinoxaline-based photoremovable protecting group (PRPG). The suitable quinoxaline-based photocage of ALA (tetraphenylethelene conjugated) has been formulated as fluorescent organic nanoparticles (FONs) and used effectively as a nano-DDS (drug delivery system) for better solubility and cellular internalization. Fascinatingly, the enhanced TP (two-photon) absorption cross section of the nano-DDS (503 GM) signifies its utility for biological applications. Using green light, we have successfully controlled the time span of cell cycles and cell growth of skin melanoma cell lines (B16F10) by the temporal release of ALA. Further, in silico studies and PDH activity assay supported the observed regulatory behavior of our nano-DDS with respect to photoirradiation. Overall, this approach expands the research path toward a futuristic photocontrolled toolbox for cell cycle regulation.

Unusual higher-order nonlinear optical properties in Au-coated triangular Ag-Au nanostructures.

Here, we report hitherto unobserved local field (LF)-assisted pump wavelength-dependent nonlinear optical (NLO) effects of three-photon (3PA)-induced four-photon absorption (4PA) at 532 nm and two-photon-induced 3PA at 730 nm in triangular-shaped core-shell Ag-Au nanoparticles (TrAg@Au) by femtosecond Z-scan. The shell thickness-dependent enhancement in the LF is observed by a COMSOL simulation. The intensity-dependent interplay between saturable and reverse-saturable absorptions along with switching of nonlinear (NL) phase is reported at 730 nm, showing the superiority of TrAg@Au in optical switching (OS). The optical limiting (OL) threshold (Fth) of 5.9(6.5)mJ/cm2 at 730 (532) nm boost their potential over benchmarked materials.

Electrical transport properties and ultrafast optical nonlinearity of rGO-metal chalcogenide ensembles.

In recent times, nanomaterials that harvest solar radiation and transform it into other forms of energy are of considerable interest. Herein, the electrical transport properties of reduced graphene oxide (rGO), rGO-zinc selenide (rGO-ZnSe) and rGO-zinc telluride (rGO-ZnTe) thin films have been investigated at 87-473 K under both dark and illumination conditions. A comparative study of photosensitivity (P) and charge carrier mobility (µ), calculated using a trap-free space charge limited current model, shows the highest values for 54 wt% ZnSe and 50 wt% ZnTe contents (namely samples C1 and C2, respectively). A decreasing trend in P values with increasing temperature is seen in all the samples (rGO, C1, and C2) and has been attributed to enhanced electron-phonon scattering. Also, photosensitivity and change in mobility under illumination show a maximum change for C2 in the entire temperature range. The nonlinear absorption coefficient (ß) of C2 is ∼1.6 times higher than that of C1 and both the samples depict a positive nonlinear refractive index when measured with 630 nm femtosecond pulses. Moreover, C2 shows a two-fold faster electron transfer rate as revealed by a time resolved fluorescence study than C1. This, along with better dispersion of ZnTe nanoparticles in the rGO matrix, explains why rGO-ZnTe has better optoelectronic properties as compared to the rGO-ZnSe composite. These results in turn make the rGO-ZnTe composite a promising candidate for optoelectronic and photonic device applications.

Photoinduced Bending of Single Crystals of a Linear Bis-Olefin via Water-Templated Solid-State [2+2] Photopolymerization Reaction.

The single crystals of two structural isomers of bis-olefinic molecules were shown to have contrasting properties in terms of their photoreactivity: one exhibits an excellent ability to form polymers, accompanied with bending of crystals upon irradiation, while the other is photostable. The photoreactive crystal is a first example in which [2+2] polymerization leads to bending of the crystals, with implications for the design of photoactuators. The hydrate formation ability of one of these molecular isomers promotes the solid-state reactivity in its crystal, as the H2 O molecules act as a template to bring the olefin molecules into the required arrangement for [2+2] polymerization. Further, the crystals of the polymer exhibited better flexibility and smoothed surfaces compared to those of the monomers. In addition, under UV-light the diene emits bluish violet light while the polymer emits green light, indicating that the luminescence property can be tuned through photoirradiation.

Nonlinearly coupled, gain-switched Nd:YAG second harmonic laser with variable pulse width.

An all-solid-state, gain-switched, green laser is developed using a side diode-array pumped Nd:YAG laser and a KTiOPO(4) (KTP) crystal as an intracavity frequency doubler. The effect of nonlinear coupling on the pulse width of the fundamental is studied and is found to be in good agreement with the experimental measurement. In this preliminary experiment, a peak power of 40 W at 532 nm corresponding to a pulse width of 409 ns is obtained for an average pump power of 2 W. Compared to a Q-switched laser, it is simple and does not require a high voltage RF driver or saturable absorbers in its operation. The laser may be useful where relatively longer nanosecond pulses are required such as eye surgery, micromachining, and underwater communication.

Simultaneous multi-wavelength oscillation of Nd laser around 1.3 mum: A potential source for coherent terahertz generation.

Simultaneous oscillations of 1318.8nm, 1320.0nm, 1332.6nm, 1335.0nm, 1338.2nm and 1339.0nm in a side, pulsed-diode-laser-array pumped Nd:YAG laser is realized for both free running and Q-switched operation. An average power of 1.1W is obtained for an absorbed pump power of 7.1W with an effective optical slope efficiency of 33%. The difference frequency interactions among these wavelengths may be used to generate radiation in the range 0.13-3.43THz. With the two most intense lines at 1318.8nm and 1338.2nm, it is possible to generate coherent radiation at 3.3THz with numerically estimated peak power of 0.21W in a 1.5mm thick GaSe crystal.