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.

A two-photon responsive hydroxyphenylquinazolinone (HPQ)-based fluorescent organic nanoprodrug for H2S release against oxidative stress.

Light-activated H2S donors have attracted considerable interest in understanding the physiological role and clinical potential of H2S, as their release is highly localized and controlled. Herein, we have evolved a new HPQ chromophore-based fluorescent organic nanosystem localized in a target area that tolerates oxidative stress and precisely releases H2S under one- and two-photon irradiation with real-time monitoring capability. The two-photon absorption cross-section of this new phototrigger was calculated to be 283 GM at 720 nm. H2S photorelease was also demonstrated in vitro on the MDA-MB-468 cell line in the presence of excess ROS. Our developed H2S nanoprodrug can be applied to living systems to release the H2S-gasotransmitter under laser irradiation in a phototherapeutic window.

Adipic acid directed self-healable supramolecular metallogels of Co(II) and Ni(II): intriguing scaffolds for comparative optical-phenomenon in terms of third-order optical non-linearity.

Two brilliant outcomes of supramolecular self-assembly directed, low molecular weight organic gelator based self-healable Co(II) and Ni(II) metallogels were achieved. Adipic acid as the low molecular weight organic gelator and dimethylformamide (DMF) solvent are employed for the metallogelation process. Rheological analyses of both gel-scaffolds reveal mechanical toughness as well as visco-elasticity. Thixotropic behaviours of both the gels were scrutinized. Morphological variations due to the presence of two different metal ions with diverse metal-ligand coordinating interactions were established. The mechanistic pathways for forming stable metallogels of Co(II)-adipic acid (Co-AA) and Ni(II)-adipic acid (Ni-AA) were judiciously developed through infrared absorption spectral analysis. The nonlinear optical properties, such as the third-order process, of these synthesized metallogels were scrutinized by means of the Z-scan method at a beam excitation wavelength of 750 nm by a femtosecond laser with different excitation intensities ranging from 64 to 140 GW cm-2. The third-order nonlinear optical susceptibility (χ(3)) of the order of 10-14 esu was obtained from the measured Z-scan data. Both the metallogels exhibit positive nonlinear refraction and reverse saturable (RSA) absorption at high-intensity excitation. Co(II) and Ni(II) metallogels show nonlinear refractive indices (n2I) of (3.619 ± 0.146) × 10-6 cm2 GW-1 and (3.472 ± 0.102) × 10-6 cm2 GW-1, respectively, and two photon absorption coefficients (ß) of (1.503 ± 0.045) × 10-1 cm GW-1 and (1.381 ± 0.029) × 10-1 cm GW-1 at an excitation intensity of 140 GW cm-2. We also studied the optical limiting properties with a limiting threshold of 9.57 mJ cm-2. Therefore, both metallogels can be considered promising materials for photonic devices: for instance, for optical switching and optical limiting.

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.

A Natural Alkaloid, ß-Carboline, as a One- and Two-Photon Responsive Fluorescent Photoremovable Protecting Group: Sequential Release of the Same or Different Carboxylic Acids.

The ß-carboline moiety, substituted at the C1 and C3 benzylic positions with a leaving group, has been demonstrated for the first time as a photoremovable protecting group for time-dependent sequential release of two (same or different) carboxylic acids upon one- and two-photon light irradiation. Density functional theory calculations suggest that the electronic environment of the ß-carboline moiety at C1 and C3 positions plays a key role in the rate of photorelease.

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.

Stepwise dual stimuli triggered dual drug release by a single naphthalene based two-photon chromophore to reverse MDR for alkylating agents with dual surveillance in uncaging steps.

In this work, we depleted glutathione (GSH) by releasing SO2 with internal stimulus GSH itself, and also selectively marked the cancer cells followed by release of anticancer drug using another orthogonal stimulus i.e., two-photon (TP) NIR light by a single naphthalene based chromophore (TP absorbance 77 GM and uncaging cross-section 21 GM). We demonstrated the improved therapeutic efficacy of chlorambucil by the stepwise dual stimuli approach and dual surveillance of both the drug uncaging process in real-time using in vitro studies.