Recently, hydrogen sulfide (H2S) has been recognised as a promising member of the gasotransmitter family, which plays a vital role in regulating various physiological and pathological processes. Hence, the development of synthetic chemical tools capable of donating H2S in a controlled manner is an area of substantial interest. Herein, we developed a two-photon-activated photoresponsive COS/H2S donor that exploits the long-range excited-state intramolecular proton transfer (ESIPT) phenomenon in our designed system. This platform uses a photocage tethered to a thiocarbamate moiety, which, upon light irradiation, releases COS. The released COS could be rapidly hydrolysed by carbonic anhydrase and generate H2S, closely mimicking the body's well-regulated endogenous H2S production. Additionally, the incorporation of the long-range ESIPT process offers several advantages, such as (i) strong emission with a large Stokes shift and (ii) a faster photorelease rate. TD-DFT calculations carried out using the CAM-B3LYP density functional with the TZVP basis set further validated our experimental findings. Intrigued by these properties, we also developed our photoresponsive COS/H2S donor HQ-COS as a nanoprodrug (nano-HQCOS) and explored its therapeutic potential in the MDA-MB-231 triple-negative breast cancer cell line. In vitro studies demonstrated that our nano-HQCOS exhibits effective cellular internalisation and inhibits the growth of triple-negative breast cancer cells, particularly those with overexpressed carbonic anhydrase, while it is benign to the normal healthy cells.

Electrical manipulation of magnetization via current-induced spin orbit torques offers a promising route toward nonvolatile and energy efficient spintronic devices. In this work, we present a comprehensive investigation of SOTs in Py/FePS_3 bilayer devices, where Py/FePS_3 is a layered van der Waals antiferromagnetic insulator. Using low frequency harmonic Hall measurements, we quantify both field like and damping like torque components and examine their dependence on temperature. We find that interfacing Py with Py/FePS_3 leads to a pronounced enhancement of the field-like torque efficiency compared to Py reference devices, while the damping-like torque remains largely unaffected. Strikingly, the field like torque efficiency exhibits a strong temperature dependence, including a clear sign reversal upon cooling. This behavior occurs despite negligible charge current flow through the Py/FePS_3 layer, indicating that the observed torque modulation arises from interfacial effects rather than bulk transport. The close correlation between the temperature evolution of the field like torque and the antiferromagnetic ordering of Py/FePS_3 highlights the active role of antiferromagnetic insulators in controlling spin orbit torque symmetry and efficiency, and suggests new pathways for torque engineering in magnetic heterostructures.

The strong visible photoluminescence (PL) in surface-oxidized nanostructured silicon emerges from the interplay between intrinsic Bloch states and oxide-related interfacial defects, making it difficult to isolate their role. Temperature-dependent (5-350 K) PL measurements on nanostructured silicon with varying crystallite sizes manifest three distinct decay mechanisms involving band-to-band, band-to-trap and trap-to-trap transitions to multiple emission bands appearing in the convoluted broad PL spectrum. At lower temperatures (less than or similar to 225 K), PL peak energy associated with the quantum-confined Bloch states exhibits a nearly linear blue shift, governed by a strong inverse power law dependence of the temperature coefficient on the effective crystallite size, while this trend reverses at higher temperatures. Conversely, the defect-related peak energies increase monotonically at a nearly constant rate throughout the experimental temperature range. A general analytical model for finite systems with a separable pseudo-potential effectively estimates the contributions from different decay channels to the PL emission. Theoretical results align well with the experimentally obtained values of the power-law exponents, offering a novel way to distinguish between the radiative recombination channels involving quantumconfined Bloch states and interfacial defects/trap states in nanostructured silicon.

Alloying offers an effective way to improve the functionality of transition metal dichalcogenides (TMDCs) in both fundamental research and optoelectronic applications, as it allows for engineering their electronic and optical properties. This study investigates the optoelectronic properties of CVD-synthesized alloy MoSSe, which exhibits an inherent out-of-plane dipole moment, arising from asymmetry in S and Se atoms on either side of the Mo layer, as confirmed by piezoelectric force microscopy, polarization-resolved second harmonic generation studies and theoretical first-principles calculations. Time-resolved photoluminescence measurements reveal an extended exciton radiative recombination lifetime in MoSSe, attributed to electron-hole wavefunction separation by the dipole moment, which improves photodetection by facilitating enhanced electron-hole separation before recombination. The device demonstrates significant responsivity over broad spectral range. By employing the photogating effect, the device response can be switched from slow to fast modes. These findings are further supported by illumination intensity-dependent photoluminescence and Raman measurements, underscoring the potential of polar TMDCs in future optoelectronic devices.

Two-photon absorption (TPA) technology has emerged as a promising approach for precise drug delivery due to its deep tissue penetration and high spatial selectivity. This study introduces a rational design approach to enhance TPA-mediated drug delivery by incorporating an increasing number of heavy bromine atoms into the hydroxymethylquinoline (HMQ) framework. The resulting molecules exhibit significantly improved TPA properties (TPA cross section of up to 130 GM), enabling efficient tumor and nuclear targeting in triple-negative breast cancer (TNBC) models. Structural modifications incorporating heavy Br atoms optimized electronic transitions, enhancing TPA cross sections and photostability. Biological evaluations revealed selective accumulation in TNBC cells, efficient nuclear localization, and enhanced therapeutic efficacy (∼75% cell killing) with minimal off-target effects. This strategy highlights the synergy between molecular design and photophysics for advancing theranostic applications. The study provides a blueprint for developing multifunctional TPA-based drug delivery systems, offering new avenues for the treatment of aggressive cancers, such as TNBC.

NdNiO3 is a rare-earth nickelate where competing interactions yield a thermally induced metal-insulator transition accompanied by simultaneous structural and magnetic transitions. In recent years, femtosecond time resolved measurements have emerged as powerful tools for studying nonequilibrium phases in such complex systems. In this work, we demonstrate that even at 110 K, well below the insulator-metal transition temperature, an infinitesimal approximate to 0.1 % optical doping in nickel's d-band can destabilize the insulating phase into a long-lived metallic phase that builds up in the first 5 ps after the pulsed excitation. Using the hysteresis free nature of the first-order transition in our sample, we infer the true lattice temperature from resistance measurement. The threshold temperature for the runaway metallization is identified with the start of the phase coexistence region. We thus conclude that simultaneous electron-hole injection is at least an order of magnitude more effective in suppressing the transition than doping by electrons or holes alone. The results also demonstrate that the homeostasis-like situations responsible for the stability in such complex systems are nevertheless susceptible to catastrophic failures under certain types of infinitesimal perturbations. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International (CC BY-NC-ND) license (https://creativecommons.org/licenses/by-nc-nd/4.0/).

The excited-state proton transfer (ESPT) process, along with a high two-photon absorption cross-section, unlocks a pathway in the field of photocages. So far, only a limited number of photocages have been reported that combine the advantages of excited-state proton transfer (ESPT) and a high two-photon absorption cross-section, enabling the direct photorelease of alcohols without relying on carbonate or carbamate linkages. Henceforth, we strategically modified a "push-pull" based 6-hydroxy-substituted 1,8-naphthalimide (NID) chromophore as an ESPT-induced two-photon responsive photocage NID (5a-d, 6) for the direct release of alcohols. Our developed photocages exhibited a large Stokes shift due to the ESPT process and also demonstrated a change in fluorescence from yellow-orange to blue upon exposure to light, enabling their suitability for image-guided delivery of bioactive molecules. Inspired by these interesting properties, we formulated our photocage as nanoparticles (nano-NID-ES) with enhanced cell penetration ability to release the bioactive molecule estrone (ES). An in vitro study demonstrated that our photoresponsive nanocarrier (nano-NID-ES) exhibited better cellular internalization and real-time monitoring ability in the MCF-7 breast cancer cell line. MTT assay further revealed that nano-NID-ES exhibited an enhanced cytotoxic effect only after exposure to light. This development establishes an emerging pathway for the design of photocages and the advancement of photoresponsive drug delivery systems.

Light emission from nanostructured silicon has triggered tremendous research interest for three decades. Yet, the exact mechanism of photoluminescence from silicon-based nano-systems is still not completely understood. It is generally believed that quantum confinement and surface chemistry play a combined role in determining the luminescence characteristics on nano silicon. In this work, we show that the evolution of electron-hole effective joint density of states, resulting from the relaxation of k-selection rule, can account for the much-observed temperature dependent shift of the luminescence spectra of nanostructured silicon. Deconvolution of the emission characteristics reveals three distinct radiative recombination channels that can be attributed to band-to-band, band-to-trap and trap-to-trap transitions. At temperatures below ∼200 K, the peak due to band-to-band transition exhibit a nearly linear blue shift with increasing temperature while at higher temperatures this trend is reversed. The rate of variation of emission peak energy with temperature is also found to be dependent on average crystallite size. These results are explained in terms of shift in the effective joint density of state function of photogenerated electron-hole pairs. The shift provides experimental evidence of the pseudo-direct transitions in the quantum-confined nanostructure of silicon.

We studied longitudinal and Hall photothermal voltages under a planar magnetic field scan in epitaxial thin films of the Topological Insulator (TI) Sb2Te3, grown using pulsed laser deposition (PLD). Unlike prior research that utilised polarised light-induced photocurrent to investigate the TI, our study introduces advancements based on unpolarized light-induced local heating. This method yields a thermoelectric response exhibiting a direct signature of strong spin-orbit coupling. Our analysis reveals three distinct contributions when fitting the photothermal voltage data to the angular dependence of the planar magnetic field. The interaction between the applied magnetic field and the thermal gradient on the bulk band orbitals enables the differentiation between the ordinary Nernst effect from the out-of-plane thermal gradient and an extraordinary magneto-thermal contribution from the planar thermal gradient. The fitting of our data to theoretical models indicates that these effects primarily arise from the bulk states of the TI rather than the surface states. These findings highlight PLD-grown epitaxial topological insulator thin films as promising candidates for optoelectronic devices, including sensors and actuators. Such devices offer controllable responses through position-dependent, non-invasive local heating via focused incident light and variations in the applied magnetic field direction.

Trivalent lanthanide ions exhibit the ability to convert near-infrared absorption into visible radiation through photon upconversion. Despite decades of extensive investigations, the role of optical coherence in this process has been overlooked. Here, we investigate the spatial coherence of upconversion photoluminescence from Erbium (Er3+) ions. Experimental results and simulations reveal that the emitted light displays correlations over longer distances than expected from an incoherent source. Moreover, the Er3+ emission profile exhibits two prominent spectral features at room temperature. Leveraging the bimodal nature of Er3+ luminescence, we observe coherence-induced modifications in the far-field spectrum, typically associated with broadband sources. These findings highlight the overlooked coherence properties of trivalent lanthanide ions and their potential impact on photon upconversion applications.

A series of chiral peptide luminophores containing the coumarin moiety was synthesized via a simple and efficient solution-based procedure. The peptides, containing either L-Phe, or L-Ala, or L-Leu (designated, respectively, as p1, p2, and p3), self-aggregate to form anti-parallel sheet-like structures. The self-assembly of the peptide luminophores leads to non-centrosymmetric crystals which display significant second harmonic generation (SHG). The dependence of the SHG intensity on the input laser polarization revealed a strong correlation between the SHG and the crystal packing. In the polar plots, the SHG intensity as a function of the linear polarization orientation of the input laser beam gave a four-petal pattern for p1, a predominantly two-petal pattern for p2, and a dumbbell-shaped pattern for p3. This reflects the dependence of the second order optical susceptibility tensor on the crystal symmetry. The polar plots can be fitted very well with the theoretical expressions derived from the second order polarization equation after incorporating crystal symmetry in the second order optical susceptibility tensor. The strong polarization-dependent SHG from organic crystals may be interesting for polarization controlled nonlinear optical switches, sensors, and actuators.

Non-centrosymmetric molecular crystals have a plethora of applications, such as piezoelectric transducers, energy storage and nonlinear optical materials owing to their unique structural order which is absent in other synthetic materials. As most crystals are brittle, their efficiency declines upon prolonged usage due to fatigue or catastrophic failure, limiting their utilities. Some natural substances, like bone, enamel, leaf and skin, function efficiently, last a life-time, thanks to their inherent self-healing nature. Therefore, incorporating self-healing ability in crystalline materials will greatly broaden their scope. Here, we report single crystals of a dibenzoate derivative, capable of self-healing within milliseconds via autonomous actuation. Systematic quantitative experiments reveal the limit of mechanical forces that the self-healing crystals can withstand. As a proof-of-concept, we also demonstrate that our self-healed crystals can retain their second harmonic generation (SHG) with high efficiency. Kinematic analysis of the actuation in our system also revealed its impressive performance parameters, and shows actuation response times in the millisecond range.

Installing proton-coupled electron transfer (PCET) in Ir-complexes is indeed a newly explored phenomenon, offering high quantum efficiency and tunable photophysics; however, the prospects for its application in various fields, including interrogating biological systems, are quite open and exciting. Herein, we developed various organelle-targeted Ir(iii)-complexes by leveraging the photoinduced PCET process to see the opportunities in phototherapeutic application and investigate the underlying mechanisms of action (MOAs). We diversified the ligands' nature and also incorporated a H-bonded benzimidazole-phenol (BIP) moiety with π-conjugated ancillary ligands in Ir(iii) to study the excited-state intramolecular proton transfer (ESIPT) process for tuning dual emission bands and to tempt excited-state PCET. These visible or two-photon-NIR light activatable Ir-catalysts generate reactive hydroxyl radicals (˙OH) and simultaneously oxidize electron donating biomolecules (1,4-dihydronicotinamide adenine dinucleotide or glutathione) to disrupt redox homeostasis, downregulate the GPX4 enzyme, and amplify oxidative stress and lipid peroxide (LPO) accumulation. Our homogeneous photocatalytic platform efficiently triggers organelle dysfunction mediated by a Fenton-like pathway with spatiotemporal control upon illumination to evoke ferroptosis poised with the synergistic action of apoptosis in a hypoxic environment leading to cell death. Ir2 is the most efficient photochemotherapy agent among others, which provided profound cytophototoxicity to 4T1 and MCF-7 cancerous cells and inhibited solid hypoxic tumor growth in vitro and in vivo.

Optical control of helicity-dependent photocurrent in topological insulator (TI) Sb2Te2Se has been studied at room temperature on epitaxial thin-films grown by pulsed laser deposition (PLD). Comparison with a theoretical model, which fits the data very well, reveals different contributions to the measured photocurrent. Study of the dependence of photocurrent on the angle of incidence (wave-vector) of the excitation light with respect to the sample normal helps to identify the origin of different components of the photocurrent. Enhancement and inversion of the photocurrent in the presence of the photothermal gradient for light incident on two opposite edges of the sample occur due to selective spin-state excitation with two opposite circularly polarized lights in the presence of the unique spin-momentum locked surface states. These observations render the PLD-grown epitaxial TI thin-films promising for optoelectronic devices such as sensors, switches, and actuators whose response can be controlled by polarization as well as the angle of incidence of light under ambient conditions. The polarization response can also be tuned by the photothermal effect by suitably positioning the incident light beam on the device.

In recent times, organelle-targeted drug delivery systems gained tremendous attention due to the site specific delivery of active drug molecules resulting in enhanced bioefficacy. In this context, the phototriggered drug delivery system (DDS) for releasing an active molecule is superior as it provides spatial and temporal control over the release. So far, near infrared (NIR) light responsive organelle targeted DDS has not yet been developed. Hence, we introduced a two-photon NIR-light responsive lysosome targeted ʽAIE + ESIPTʼ active single component DDS based on naphthalene chromophore. The Two-photon absorption cross-section of our DDS is 142 GM at 850 nm. The DDS was converted into pure organic nanoparticles for biological applications. Our nano-DDS is capable of selective targeting, AIE-luminogenic imaging, and drug release within the lysosome. In vitro studies using cancerous cell lines showed that our single component photoresponsive nanocarrier exhibited enhanced cytotoxicity and real-time monitoring ability of the drug release.

The role of spatial folding of molecules on their nonlinear optical properties such as two-photon absorption and self-focusing due to nonlinear refraction has been studied experimentally on a newly designed foldamer having a D–π–A–π–D structure.

Semiconductor nanostructures with near-unity photoluminescence quantum yields (PLQYs) are imperative for light-emitting diodes and display devices. A PLQY of 99.7 ± 0.3% has been obtained by stabilizing 91% Sn2+ in the Dion-Jacobson (8N8)SnBr4 (8N8-DJ) perovskite with 1,8-diaminooctane (8N8) spacer. The PLQY is favored by a longer spacer molecule and out-of-plane octahedral tilting. The PLQY shows one-month ambient stability under high relative humidity (RH) and temperature. With n-octylamine (8N) spacer, Ruddlesden-Popper (8N)2SnBr4 (8N-RP) also shows PLQY of 91.7 ± 0.6%, but it has poor ambient stability. The 5-300 K PL experiments decipher the self-trapped excitons (STEs) where the self-trapping depth is 25.6 ± 0.4 meV below the conduction band because of strong carrier-phonon coupling. The microsecond long-lived STE dominates over the band edge (BE) peaks at lower excitation wavelengths and higher temperatures. The higher PLQY and stability of 8N8-DJ are due to the stronger interaction between SnBr64- octahedra and 8N8 spacer, leading to a rigid structure.

We demonstrated for the first time without any chemical modification the two-photon absorption (TPA) cross-section can be enhanced and red-shifted to the near-infrared (NIR) region by the ground-state proton-transfer (GSPT) process. Using GSPT, we developed a simple binol-based aggregation-induced emission (AIE)-fluorogenic phototrigger having a large two-photon uncaging cross-section in the "phototherapeutic window". As a proof of concept, we showed our phototrigger for the release of two different anticancer drugs in the NIR region.

Optical control of helicity-dependent photocurrent in topological insulator Sb$_2$Te$_2$Se has been studied at room temperature on dominantly c-axis oriented granular polycrystalline samples grown by pulsed laser deposition technique. Strong spin-orbit coupling and spin-momentum locking make this system unique for their applications. We observed that photocurrent can be controlled by exciting the sample with different circular and linear polarized light, yielding a polarization-dependent current density which can be fitted very well with a theoretical model. Magnitude of the photocurrent is higher even at room temperature, compared to previous reports on other single-crystal topological insulators. Comparison with the theoretical model suggests that photocurrent has different contributions. Study of dependence of photocurrent on the angle of incidence (wave-vector) of the excitation laser beam with respect to the surface normal of the sample helps to identify origins of different terms contributing to the observed photocurrent. Incidence-angle driven helicity switching, which is a very simple and effective technique to control the directional photocurrent, has also been observed in this study. This photocurrent can also be controlled with the help of photothermal gradient generated by the excitation light beam. Enhancement and inversion of this photocurrent in presence of photothermal gradient for light incident on two opposite edges of the sample occur due to selective spin state excitation with two opposite (left and right) circularly polarized light in presence of the unique spin-momentum locked surface states. These observations renders this polycrystalline material to be more important in polarization-dependent photodetection applications as well as for spin-optoelectronics under ambient conditions.

Nonlinear refraction in all-inorganic halide perovskites, the CsPbBr3 and CsPbBr1.5I1.5 nanocube and nanosheet colloids in toluene, has been studied by a time-resolved, two-color pump-probe beam-deflection technique using above-bandgap excitation by low-power, continuous-wave (CW) diode lasers, as opposed to high-power pulsed lasers commonly used in nonlinear optical measurements. An enhancement of nonlinear refraction coefficient by eight orders from the values previously reported in the literature in similar materials for below-bandgap excitation has been observed at CW laser power as low as 10 mW. This may facilitate mass-scale deployment of these materials and method to nonlinear optical devices and applications. Nanocubes show higher nonlinear refraction as compared to the corresponding nanosheet samples, presumably due to the reduced dimensionality. The nonlinear refraction and its time-evolution have originated from the thermal lensing effect, which can be attributed to the anharmonic vibration of atomic nuclei. Observation of intensity-dependent thermal diffusion rate indicates nonlinear heat transport at the mesoscopic scale. Effects of convective heat flow have been measured at laser power exceeding 25 mW. These results may inspire further theoretical and experimental studies of thermal transport in the mesoscopic domain.