Joshy Joseph

Ordered assembly of fullerenes is of significant importance in organic electronic applications, as charge carrier mobility in fullerene-based materials is highly sensitive to structural order. However, commonly employed solution-processing techniques often suffer from strong aggregation tendencies or uncontrolled crystallization of fullerenes during film formation. In contrast, advanced nanofabrication techniques that enable precise control over fullerene morphology at the nanoscale are typically complex and costly. In this work, we propose a facile supramolecular strategy based on the polymer-assisted assembly of a pyridinium-functionalized fullerene amphiphile (FPy) to achieve ordered fullerene architectures, thereby enhancing charge carrier mobility through reduced energetic disorder. A commercially available anionic polymer, polystyrenesulfonate (PSS), was employed to assemble the cationic fullerene derivative (FPy) primarily via electrostatic interactions, further stabilized by π–π stacking between fullerene units. The interaction of FPy with PSS was confirmed by UV–visible absorption spectroscopy, while TEM, SEM, and AFM analyses revealed the formation of ultrathin two-dimensional crystalline nanosheets with highly ordered fullerene packing. X-ray diffraction (XRD) analyses clearly demonstrate a transition from polycrystalline FPy to a highly ordered and uniform face-centered cubic (FCC) lattice in the PSS/FPy hybrid, confirming the anionic polymer-induced switching toward a more ordered nanoassembly. Space-charge-limited current (SCLC) measurements further revealed an order-of-magnitude enhancement in electron mobility (0.92 × 10–3 cm2 V–1 S–1) compared to FPy alone, which can be correlated with the reduced energetic disorder in the FCC lattice structure of the PSS/FPy hybrid assembly. Overall, this study highlights the significance of polymer-assisted assembly of rationally designed amphiphilic fullerenes as a general and scalable strategy to improve electron transport in a wide range of optoelectronic devices.

Donor-π-acceptor (D-π-A) type phenothiazine derivatives, exhibiting quasi-axial and quasi-equatorial conformers with distinct photophysical properties, serves as tunable, multifunctional materials for applications in sensors and optoelectronic devices. Herein, we report two phenothiazine based D-π-A emitters, NTPH and NTPCF, incorporating phenothiazine as the donor and nicotinonitrile as the acceptor, designed as stimuli-responsive functional materials with switchable conformers exhibiting differential optical properties. Single-crystal analyses show that phenothiazine adopts a quasi-axial conformation in NTPCF, while NTPH exhibits polymorphism with quasi-axial (NTPH-B) and quasi-equatorial (NTPH-O) conformers. The quasi-axial conformer of NTPCF exhibits green emission with a fluorescence maximum at 545 nm, while NTPH shows cyan emission with a fluorescence maximum at 463 nm and a shoulder band around 516 nm.The equatorial conformer of NTPH has a characteristic TADF orange emission with a maximum of 585 nm. Theoretical studies highlight that singlet-triplet energy gap, ΔE_ST is significantly influenced by the molecular conformation and the low energy barriers (NTPCF shows high-contrast, reversible cyan-to-orange mechanochromism (Δλ_em~135 nm), suitable for anticounterfeiting, while NTPH exhibits irreversible blue-to-orange switching. Solution-processed orange organic light-emitting diodes (OLEDs) based on neat film of NTPCF achieve a high luminance of 8400 cd/m². Additionally, NTPCF-based single-molecule white OLEDs were developed by varying the doping concentration, yielding a cool white OLED with CIE (0.33, 0.37), CRI of 70, and EQE of 3.36%, as well as a warm white OLED with CIE (0.39, 0.45) and EQE of 4.25%.

Surface-enhanced Raman spectroscopy (SERS) is a surface-sensitive analytical technique that relies heavily on plasmonic substrates to enhance Raman scattering. In this study, we report the fabrication of a cost-effective SERS substrate by thermally evaporating silver (Ag) onto the eggshell membrane (ESM), a low-cost and biologically sourced material, to create substrates with controlled surface morphologies. The silver coating thickness has been varied to optimize the signal enhancement and was evaluated with three different standard Raman active molecules: 4-mercaptobenzoic acid (4-MBA), 4-mercaptophenylboronic acid (4-MPBA), and rhodamine 6G (R6G)- as analytes. The developed substrates exhibited remarkable SERS activity with an Enhancement Factor (EF) of 0.12 ×10⁶ for 4-MBA, 0.70 × 10⁵ for 4-MPBA and 0.36 × 10⁴ for R6G, respectively. The ESM with optimal silver deposition of a thickness of 20 nm exhibited significantly enhanced SERS signal, with improved sensitivity and detection limit for all the three molecular analytes. Present study also highlights the importance of precise control over the metal coating thickness on ESM by thermal evaporation to achieve optimal SERS performance. Notable contribution is the fabrication of silver-coated eggshell membrane (ESM/Ag) as a cost-effective promising SERS platform for high-performance molecular sensing applications.

Photodynamic therapy (PDT) has emerged as an efficient and noninvasive treatment approach utilizing laser-triggered photosensitizers for combating cancer. Within this rapidly advancing field, iridium-based photosensitizers with their dual functionality as both imaging probes and PDT agents exhibit a potential for precise and targeted therapeutic interventions. However, most reported classes of Ir(III)-based photosensitizers comprise mononuclear iridium(III), with very few examples of dinuclear systems. Exploring the full potential of iridium-based dinuclear systems for PDT applications remains a challenge. Herein, we report a dinuclear Ir(III) complex (IRDI) along with a structurally similar monomer complex (IRMO) having 2-(2,4-difluorophenyl)pyridine and 4'-methyl-2,2'-bipyridine ligands. The comparative investigation of the mononuclear and dinuclear Ir(III) complexes showed similar absorption profiles, but the dinuclear derivative IRDI exhibited a higher photoluminescence quantum yield (Φ_p) of 0.70 compared to that of IRMO (Φ_p = 0.47). Further, IRDI showed a higher singlet oxygen generation quantum yield (Φ_s) of 0.49 compared to IRMO (Φ_s = 0.28), signifying the enhanced potential of the dinuclear derivative for image-guided photodynamic therapy. In vitro assessments indicate that IRDI shows efficient cellular uptake and significant photocytotoxicity in the triple-negative breast cancer cell line MDA-MB-231. In addition, the presence of a dual positive charge on the dinuclear system facilitates the inherent mitochondria-targeting ability without the need for a specific targeting group. Subcellular singlet oxygen generation by IRDI was confirmed using Si-DMA, and light-activated cellular apoptosis via ROS-mediated PDT was verified through various live-dead assays performed in the presence and absence of the singlet oxygen scavenger NaN₃. Further, the mechanism of cell death was elucidated by an annexin V-FITC/PI flow cytometric assay and by investigating the cytochrome c release from mitochondria using Western blot analysis. Thus, the dinuclear complex designed to enhance spin-orbit coupling with minimal excitonic coupling represents a promising strategy for efficient image-guided PDT using iridium complexes.

With an objective to develop efficient photosensitizers to cancerous tissues, we synthesized two novel biocompatible sensitizers based on aza-BODIPYs incorporated with heavy atoms and biotin moieties. The bioconjugates DPR2a and DPR2b exhibited a favorable absorption range (600-750 nm) with excellent triplet-state quantum yields (up to 79%) and singlet oxygen generation yields (up to 75%). In vitro photobiological investigations employing MDA-MB-231 breast cancer cell lines exhibited rapid cellular uptake, negligible dark toxicity, and high photocytotoxicity. The mechanism of cell death of these systems was predominantly due to the mitochondrial damage, leading to apoptosis mediated via the generation of singlet oxygen-triggered reactive oxygen species. The in vivo studies with the representative conjugate DPR2a employing female NOD/SCID mice models showed inhibition in tumor growth and significantly decreased tumor volume post photodynamic therapy (PDT) treatment. Our results validate that both DPR2a and DPR2b with iodine incorporation exhibit favorable and superior photophysical and photobiological aspects and demonstrate thereby their potential applications in imaging and PDT of cancer.

In this paper, we demonstrate the design and fabrication of an AlGaN/GaN High Electron Mobility Transistor (HEMT) as a bio sensing platform. Bio-compatible functionalization process with thioglycolic acid and antibody-antigen immobilization process with EDC-NHS chemistry is optimized, and the AlGaN/GaN HEMT biosensor is validated using recombinant C3G (RAPGEF1) protein and an indigenously developed mouse monoclonal antibody (clone 3F6mAb). The designed biosensor with its extended source-drain pads and inter-digital gate sensing design increases sensitivity of device to detect low concentration of biological samples. C3G protein is detected by antigen-antibody conjugation over extended functionalized sensing gate area which resulted in 36.2% change in drain current output and the corresponding antigen is detected up to 500 pg/ml. The biosensor shows a resolution in mA range, which is easily implementable by circuit due to low noise factor. It can therefore be adopted for use to detect antigens in very small biological samples, required in diagnostic assays of bio-medical applications.