Browsing by Author "Laskar, Inamur Rahaman"

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A 1D thiocyanato bridge nickel(II) system: crystal structure and magnetic property
(Elsiever, 2001-04) Laskar, Inamur Rahaman
A one-dimensional coordination polymer of nickel(II), [(μN,S-NCS)2{Ni(ampy)}]n (ampy=1-(2-aminoethyl)pyrrolidine) has been synthesized and characterized by X-ray single crystal analysis. Structure analysis reveals that each nickel(II) center is coordinated in a distorted octahedral fashion with four bridging thiocyanato ligands and one mesocyclic diamine ligand. The low temperature (300–18 K) magnetic measurement shows that the system is ferromagnetically coupled. The magnetic data are fitted to the de Neef equation, giving the parameters J=1.4 cm−1 and g=2.08.
Aggregation induced emission’ active iridium(iii) complexes with applications in mitochondrial staining
(RSC, 2017) Chowdhury, Rajdeep; Laskar, Inamur Rahaman
Two new bis-cyclometalated iridium(III) complexes, [Ir(F2ppy)2(L)] and [Ir(ppy)2(L)], where F2ppy = 2-(2′,4′-difluoro)phenylpyridine, ppy = 2-phenylpyridine and L = 1,2-((pyridin-2-ylimino)methyl)phenol, have been designed and synthesized by a convenient route. We have univocally characterized their structure by 1H NMR, 19F NMR, HRMS and SXRD. Both complexes exhibit strong ‘Aggregation Induced Emission (AIE)’ activity, which has been investigated using spectroscopy measurements, ab initio quantum chemical calculations and by analysing their crystal packing. One of the complexes has been shown to have a potential application as a non-toxic bio-imaging probe for mitochondrial staining.
Aggregation induced phosphorescence” active “rollover” iridium(iii) complex as a multi-stimuli-responsive luminescence material
(RSC, 2015) Laskar, Inamur Rahaman
On reaction of 2,2′-bipyridine with iridium(III), an “aggregation induced phosphorescence (AIP)” active “rollover” complex, [Ir(PPh3)2(bipy-H)(Cl)(H)] (bipy-H = κ2-N,C-2,2′-bipyridine) or [Ir(bipy-H)], is obtained. The emission colour changes from bluish-green to yellowish-orange and vice versa after repeated protonation and deprotonation of [Ir(bipy-H)], respectively, which unequivocally supports its reversible nature. [Ir(bipy-H)] is sensitive to acids with different pKa values. Tuning of the emission properties can be achieved in the presence of acids with different pKas. This behaviour allows the complex, [Ir(bipy-H)], to function as a phosphorescent acid sensor in both solution and the solid state, as well as a chemosensor for detecting acidic and basic organic vapours. The protonated form, [Ir(bipy-H)H+], which is generated after protonation of [Ir(bipy-H)] can be used as a solvatochromic probe for oxygen containing solvents, and also shows vapochromic properties. The emission, absorption and 1H NMR spectra of [Ir(bipy-H)] under acidic and basic conditions demonstrate its reversible nature. DFT based calculations suggest that changes in the electron affinity of the pyridinyl rings are responsible for all these processes.
Aggregation-induced emission” of transition metal compounds: Design, mechanistic insights, and applications
(Elsiever, 2019-12) Laskar, Inamur Rahaman
In the last decades, compounds with ‘Aggregation-Induced Emission’ (AIE), which are weakly or non-emissive at all in solution but exhibit a strong luminescence in aggregated states, have emerged as an extraordinary breakthrough in the field of luminescent materials, allowing to circumvent ‘Aggregation Caused Quenching’ (ACQ), which in many cases prevents the development of efficient solid-state materials for optoelectronic applications.
Aggregation-induced emission” of transition metal compounds: Design, mechanistic insights, and applications
(Elsiever, 2019-12) Laskar, Inamur Rahaman
In the last decades, compounds with ‘Aggregation-Induced Emission’ (AIE), which are weakly or non-emissive at all in solution but exhibit a strong luminescence in aggregated states, have emerged as an extraordinary breakthrough in the field of luminescent materials, allowing to circumvent ‘Aggregation Caused Quenching’ (ACQ), which in many cases prevents the development of efficient solid-state materials for optoelectronic applications.
Aggregation-induced emission” of transition metal compounds: Design, mechanistic insights, and applications
(Elsiever, 2019-12) Laskar, Inamur Rahaman
In the last decades, compounds with ‘Aggregation-Induced Emission’ (AIE), which are weakly or non-emissive at all in solution but exhibit a strong luminescence in aggregated states, have emerged as an extraordinary breakthrough in the field of luminescent materials, allowing to circumvent ‘Aggregation Caused Quenching’ (ACQ), which in many cases prevents the development of efficient solid-state materials for optoelectronic applications.
Aggregation-Induced Enhanced Emission (AIEE)-Active Conjugated Mesoporous Oligomers (CMOs) with Improved Quantum Yield and Low-Cost Detection of a Trace Amount of Nitroaromatic Explosives
(ACS, 2020-06) Laskar, Inamur Rahaman
The article reports a straightforward strategy for the design and synthesis of highly luminescent conjugated mesoporous oligomers (CMOs) with an “aggregation-induced enhanced emission” (AIEE) feature through Wittig polymerization of a molecular rotor. Typical molecular rotors such as triphenylamine (TPA) and tetraphenylethene (TPE) as B2-, and A4- and A3-type nodes have been used to construct AIEE-active CMOs, namely, CMO1 and CMO2. The quick dissipation of the excited photons is successfully controlled by the restriction of rotation of the phenyl units through the formation of a mesoporous network scaffold in a solid/thin film, which provides high quantum yields for the interlocked CMO system. Both the CMOs are sensitive and selective to the various nitroaromatic explosives, whereas CMO1 is more sensitive (Ksv = 2.6 × 106 M–1) toward picric acid. The increased quenching constant for CMO1 is due to its increased quantum yield and high energy-transfer efficiency. The mechanism for sensing has been studied in detail. The larger pore size and pore density in the mesoporous network of CMO1 are found to be responsible for the greater extent of energy transfer from CMO1 to picric acid. Furthermore, CMO1 has been employed for low-cost
Cis–trans isomerism in nickel(II)–diamine nitrite: synthesis and single crystal structure of an unusual cis-dinitronickel(II) complex, [NiL2(NO2)2] (L=1,2-diamino-2-methylpropane)
(Elsiever, 2000-04-30) Laskar, Inamur Rahaman
The complexes [NiL3](NO2)2·2H2O (violet, 1) and cis-[NiL2(NO2)2]·0.5H2O (pink, 1b) (L=1,2-diamino-2-methylpropane) have been synthesized from solution. The X-ray single crystal structure analysis of compound 1b has been carried out, but the presence of a water molecule cannot be detected. Upon heating, complex 1b undergoes dehydration followed by an endothermic phase transition to produce trans-[NiL2(NO2)2] (1d). The violet species (1) also undergoes dehydration upon heating with deamination resulting (1d).
Development of a Multifunctional Aggregation-Induced Emission-Active White Light-Emissive Organic Sensor: A Combined Theoretical and Experimental Approach
(ACS, 2022-07) Laskar, Inamur Rahaman; Roy, Ram Kinkar
A far-red to near-infrared (NIR) “aggregation-enhanced emission” (AEE)-active donor–acceptor (D–A)-type probe (denoted as IMZ-CN) is designed and synthesized. The probe IMZ-CN is designed rationally using the quantum mechanical gap tuning (highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) energy gap, i.e., ΔEg) approach. The probe is tethered with two different functionalities, i.e., dicyanovinyl (DCV) and benzimidazole (IMZ), which effectively lower the value of ΔEg and cause emission in the far-red to near-infrared region. Furthermore, it selectively detects cyanide (CN–) and fluoride (F–) ions by turn-on emission in pure water without interference between each other. Apart from CN–/F– sensing, the probe (IMZ-CN) is also sensitive toward the acidic environment due to the presence of potential basic nitrogen on the benzimidazole unit. The binding of CN–/F– induces a blue shift in the electronic spectra of IMZ-CN, whereas an acidic environment (e.g., the change in pH from 7 to 2.3) causes red-shifted emission (∼60 nm). Interestingly, IMZ-CN displays a nearly pure white emission during the course of the aggregation-enhanced emission (AEE) mechanism study in the PEG–water binary mixture (99%) with CIE coordinates (0.30, 0.33). The mechanisms behind the emission of white light and the anion-binding/sensing applications (photophysical properties of the probe) are supported by quantum mechanical calculations [using “frontier molecular orbitals” (FMO), “time-dependent density functional theory” (TD-DFT), and “natural transition orbital” (NTO) calculations]. As this multifunctional probe IMZ-CN interacts with CN–, F–, H+, etc., the reactivity parameters [e.g., global chemical hardness (η), global electrophilicity (ω), etc.] were calculated by applying the concept of “density functional reactivity theory” (DFRT) to validate its reactivity.
Dual emission and multi-stimuli-response in iridium(iii) complexes with aggregation-induced enhanced emission: applications for quantitative CO2 detection
(RSC, 2017) Laskar, Inamur Rahaman
Four new Ir(III) complexes with the general formula [IrHCl(C^N)(PPh3)2] containing different conjugated Schiff base ligands (C^N) have been synthesized and characterized by 1H, 13C, and 31P NMR, HRMS, and IR spectra and one of them by single crystal X-ray diffraction. Their photophysical properties in solution and in the solid state have been analyzed and three main practical results have been obtained: (i) a dual fluorescent and phosphorescent emissive complex in solution, (ii) successful acid/base sensing in the solid state and (iii) quantitative CO2 detection. Quantum chemical calculations have been employed to assign the character of the lowest excited states. A plausible explanation for the observed aggregation induced enhanced emission (AIEE) is given, based on the restriction of intramolecular motions due to the effect of intermolecular C–H⋯π and C–H⋯Cl type interactions upon aggregation.
Dual-emissive iridium(iii) complex with aggregation-induced emission: mechanistic insights into electron transfer for enhanced hypoxia detection in 3D tumor models
(ACS, 2025-01) Roy, Aniruddha; Laskar, Inamur Rahaman
Accurate oxygen detection and measurement of its concentration is vital in biological and industrial applications, necessitating highly sensitive and reliable sensors. Optical sensors, valued for their real-time monitoring, nondestructive analysis, and exceptional sensitivity, are particularly suited for precise oxygen measurements. Here, we report a dual-emissive iridium(III) complex, IrNPh2, featuring “aggregation-induced emission” (AIE) properties and used for sensitive oxygen sensing. IrNPh2 exhibits dual emissions at 450 and 515 nm, with 515 nm triplet-state emission demonstrating remarkable oxygen sensitivity due to its long-lived excited state (12.12 μs) and high quantum yield (68%). Stern–Volmer analysis reveals a notable quenching constant (Ksv = 12.44%–1) and an ultralow detection limit of 0.0397%, emphasizing its superior performance. The oxygen quenching mechanism is driven by electron transfer (ET), supported by computational studies showing the lowest-unoccupied molecular orbital (LUMO) alignment of IrNPh2 with the πg* orbitals of triplet oxygen, leading to superoxide radical (O2•–) formation. Electron paramagnetic resonance (EPR) studies further confirm this pathway. Biological evaluations using a three-dimensional (3D) U87-MG glioma spheroid model highlight the ability of IrNPh2 to detect hypoxic regions, with significant fluorescence enhancement under hypoxia and minimal cytotoxicity (>80% viability at 100 μM). With high sensitivity, low detection limits, and biocompatibility, IrNPh2 emerges as a promising candidate for oxygen sensing in environmental and biomedical applications, especially tumor hypoxia detection.
Electrochemiluminescence studies of the cyclometalated iridium(III) complexes with substituted 2-phenylbenzothiazole ligands
(Elsiever, 2004-08) Laskar, Inamur Rahaman
Electrogenerated chemiluminescence (ECL) studies have been performed for the iridium(III) cyclometalated L2Ir(acac) complexes with substituted 2-phenylbenzothiazole ligand L. Electron transfer (ET) generation of the excited 3*L2Ir(acac) has been studied using a triple-potential-step technique in acetonitrile–dioxane (1:1) solutions containing 0.1 M (n-C4H9)4NPF6 as the supporting electrolyte. ET reactions between electrochemically generated L2Ir(acac)+ and A− (radical anions of aromatic nitriles) species lead to very efficient generation of ECL emission. Extremely high ECL efficiencies (up to 0.40) close to the excited 3*L2Ir(acac) luminescence yields have been found.
Electronic substitution effect on esipt-driven ph and amine sensing: exploring mechanism
(Wiley, 2025-01) Laskar, Inamur Rahaman
It is required to have a more straightforward and easier way to check the quality of food to ensure the safety of the public health. The decomposition of meat protein results in ammonia and biogenic amines (BAs). Consequently, to evaluate the safety and quality of meat products throughout the storage, transit, and consumption depends on the sensitive detection of the released BAs. Here, we have designed and synthesized three luminescent-based probe molecules, which originated from 2-(2-hydroxyphenyl) benzothiazole (HBT) derivatives and showed the excited state-induced proton transfer (ESIPT) phenomenon. The two substituents (OMe and NO2) were used rationally at the para position of HBT, and the electronic properties were evaluated using Hammett substituent constants. The proton donating ability of the O−H to the acceptor is largely facilitated by the presence of a strong electron-withdrawing group, which in this case is NO2. The proton transfer rate can be controlled, and in this case, to a slower rate with the influence of the electron donating group OMe. The controllability of proton transfer led us to use it in pH sensing. A prominent and multi-color change with pH variation was observed in the case of the OMe substituted compound. These probes were further employed for amine sensing, and the limit of detection (LOD) was determined to be 28.6 μM and 61.34 nM for ammonia and hydrazine, respectively. In addition, strip-based detection of spoilage of chicken meat was studied for real-world applications via both contact and non-contact modes.
Encapsulation of multi-stimuli AIE active platinum(ii) complex: a facile and dry approach for luminescent mesoporous silica
(RSC, 2016) Roy, Ram Kinkar; Laskar, Inamur Rahaman
Luminescent materials have great potential in diverse applications in their solid state. Because these materials are subject to the aggregation-caused quenching (ACQ) effect, increasing attention is focused on synthesizing aggregation-induced emission (AIE) active materials to avoid the ACQ effect. Herein a new class of AIE active, excimeric platinum(II) complex, [Pt(C^N)(L1)(Cl)], 3 [C^N = 2-phenylpyridine; L1 = N1-tritylethane-1,2-diamine] is reported. The complex 3 exhibited mechanofluorochromism (MFC) and thereby transformed into an orange-emitting complex, 3a, upon grinding. Crushing of 3 (or 3a) with meso-structured silica produced a luminescent composite material, 3b, and thereby the AIE Pt(II) complex moved into the mesopores and the process signaled with a drastic change of emission color (yellow → green). The solid-state luminescent behaviour of these complexes was thoroughly studied. The photophysical properties were also supported by TD-DFT based theoretical study.
Engineering a light-driven cyanine based molecular rotor to enhance the sensitivity towards a viscous medium
(RSC, 2021) Chowdhury, Rajdeep; Laskar, Inamur Rahaman; Majumder, Syamantak; Mukherjee, Sudeshna
This article describes the enhanced sensitivity to a viscous medium by a molecular rotor based fluorophore (RBF), TPSI I. The TPSI I molecule is designed in such a way that it consists of a rotor and a fluorophore with a π-rich bridge between them. TPSI I is a light-responsive material in solution as well as in the solid state. The structural design of the molecule allows flexible rotation and photo-induced cis–trans isomerization both in the solid state as well as in solution. These combined attributes of TPSI I are responsible for the ultrasensitive viscosity response of the new material, which was verified through the Förster–Hoffmann equation. According to this equation, the derived ‘x’ value is 1.02 (x is related to the sensitivity) which is the highest among the contemporary reports for RBFs. The facts were evidenced both by experimental as well as theoretical data. The ultrasensitivity towards viscosity was further analyzed in in vitro studies by detecting the subtle changes in the alteration of intracellular viscosity in normal and cancerous cells. An alteration of intracellular viscosity in cells treated with viscosity modulators was also confirmed using a previously well-established viscosity measurement technique, dynamic measurement through the piezoelectric patch. Our research offers a detailed mechanism to improve viscosity sensors and an efficient probe for detecting minute changes in intracellular viscosity.
Enhanced phosphorescence and electroluminescence in triplet emitters by doping gold into cadmium selenide/zinc sulfide nanoparticles
(Elsiever, 2005-10) Laskar, Inamur Rahaman
Gold–cadmium selenide/zinc sulfide (Au–CdSe/ZnS) nanocomposites (NCs) were synthesized and characterized by transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, ultraviolet–visible (UV–visible) absorption and photoluminescence (PL) emission spectroscopy. The PL intensity in the Au–CdSe/ZnS NCs system was found to be much greater than that of CdSe/ZnS nanoparticles (NPs) alone, because of the surface-enhanced Raman scattering of Au NPs. Adding Au–CdSe/ZnS NCs to the cyclometalated iridium(III) complex (Ir-complex) greatly enhanced the PL intensity of a triplet emitter. Three double-layered electroluminescence (EL) devices were fabricated where the emitting zone contains the definite mixture of Ir-complex and the NCs [molar concentration of Ir-complex/NCs = 1:0 (Blank, D-1), 1:1 (D-2) and 1:3 (D-3)] and the device D-2 exhibited optimal EL performances.
Enhanced TNT vapor detection via a donor–acceptor-based imine cross-conjugated aggregation-induced enhanced emission active porous polymer
(ACS, 2025-09) Laskar, Inamur Rahaman
The development of sensitive and selective probes for the detection of nitro explosives is critical for ensuring public safety and environmental monitoring. Among various detection strategies, porous materials offer significant advantages for vapor-phase detection due to their high surface area and analyte-trapping capability. In this study, we report the design and synthesis of an electron-rich system with a donor–acceptor (D–A)-based organic porous polymer (P1), incorporating triphenylamine as the electron-donating unit and imine-conjugated sulfone (SO2) functionalities as electron acceptors. The resulting aggregation-induced enhanced emissive (AIEE) porous network exhibits selective fluorescence quenching in the presence of nitro explosives, particularly picric acid (PA) and 2,4,6-trinitrotoluene (TNT) in aqueous media. Notably, in the vapor phase, P1 demonstrates a strong and selective response to TNT vapors with a detection limit of 50 ppb, attributed to its higher vapor pressure compared to PA. Experimental and density functional theory (DFT) mechanistic investigations revealed distinct sensing pathways: Förster resonance energy transfer governs PA detection, while photoinduced electron transfer is responsible for TNT sensing. The high porosity of the polymer, confirmed through FESEM imaging and BET surface area analysis, facilitates efficient analyte capture, contributing to its superior vapor-phase sensitivity.
Enhanced TNT vapor sensing through a PMMA-mediated AIPE-active monocyclometalated iridium(III) complex: a leap towards real-time monitoring
(RSC, 2024-02) Laskar, Inamur Rahaman
Based on the explosive nature and harmful effects of nitro-based explosive materials on living beings and the environment, it is extremely important to develop luminescence-based probe molecules for their detection with excellent selectivity and sensitivity. Two AIPE (aggregation-induced phosphorescence emission)-active iridium(III) complexes (M1 and M2) were developed for the sensitive detection of TNT in both contact and non-contact modes. The aggregate solutions of both complexes (M1 and M2 in THF/H2O, 1/9 by volume) detected TNT at the pico-molar (pM) level. These complexes showed greatly enhanced emission intensity while embedded in a PMMA(polymethyl methacrylate) matrix film. The amplified quantum efficiency, improved phosphorescence lifetime, and enhanced porous network of M2-PMMA composite helps to improve the sesitivity of TNT vapor detection. Interestingly, the sensitivity of the detection of TNT by the M2 complex was significantly improved (5-fold) in a PMMA-incorporated complex (CP) with an observed limit of detection (LOD) of 12.8 ppb. From the BET analysis of CP, it was observed that the mesoporous network of CP has an average pore diameter of 8.52 nm and a surface area of 2.03 m2 g−1. The porous network of CP assists in trapping TNT vapor in a polymeric network containing an electron-rich probe (iridium(III) complex, M2), which helps to effectively trap TNT, thus enhancing electronic communication. As a result, significant emission quenching was observed
Evaluation of novel platinum(ii) based AIE compound-encapsulated mesoporous silica nanoparticles for cancer theranostic application
(RSC, 2018) Chowdhury, Rajdeep; Laskar, Inamur Rahaman
Advanced biomedical research has established that cancer is a multifactorial disorder which is highly heterogeneous in nature and responds differently to different treatment modalities, due to which constant monitoring of therapy response is becoming extremely important. To accomplish this, different theranostic formulations have been evaluated. However, most of them are found to suffer from several limitations extending from poor resolution, radiation damage, to high costs. In order to develop a better theranostic modality, we have designed and synthesized a novel platinum(II)-based ‘aggregation induced emission’ (AIE) molecule (named BMPP-Pt) which showed strong intra-cellular fluorescence and also simultaneously exhibited potent cytotoxic activity. Due to this dual functionality, we wanted to explore the possibility of using this compound as a single molecule based theranostic modality. This compound was characterized using elemental analysis, NMR and IR spectroscopy, mass spectrometry and single crystal X-ray structure determination. BMPP-Pt was found to exhibit a high AIE property with emission maxima at 497 nm. For more efficient cancer cell targeting, BMPP-Pt was encapsulated into mesoporous silica nanoparticles (Pt-MSNPs) and the MSNPs were further surface modified with an anti-EpCAM aptamer (Pt-MSNP-E). Pt-MSNPs exhibited higher intracellular fluorescence compared to free BMPP-Pt, though both of them induced a similar degree of cell death via the apoptosis pathway, possibly via cell cycle arrest in the G1 phase. Anti-EpCAM aptamer modification was found to increase both cytotoxicity and intracellular fluorescence compared to unmodified MSNPs. Our study showed that EpCAM functionalized BMPP-Pt loaded MSNPs can efficiently internalize and induce apoptosis of cancer cells as well as show strong intracellular fluorescence. This study provides clues towards the development of a potential single compound based theranostic modality in future.
Evaluation of novel platinum(II) based AIE compound-encapsulated mesoporous silica nanoparticles for cancer theranostic application
(RSC, 2018) Chowdhury, Rajdeep; Laskar, Inamur Rahaman; Roy, Aniruddha
Advanced biomedical research has established that cancer is a multifactorial disorder which is highly heterogeneous in nature and responds differently to different treatment modalities, due to which constant monitoring of therapy response is becoming extremely important. To accomplish this, different theranostic formulations have been evaluated. However, most of them are found to suffer from several limitations extending from poor resolution, radiation damage, to high costs. In order to develop a better theranostic modality, we have designed and synthesized a novel platinum(II)-based ‘aggregation induced emission’ (AIE) molecule (named BMPP-Pt) which showed strong intra-cellular fluorescence and also simultaneously exhibited potent cytotoxic activity. Due to this dual functionality, we wanted to explore the possibility of using this compound as a single molecule based theranostic modality. This compound was characterized using elemental analysis, NMR and IR spectroscopy, mass spectrometry and single crystal X-ray structure determination. BMPP-Pt was found to exhibit a high AIE property with emission maxima at 497 nm. For more efficient cancer cell targeting, BMPP-Pt was encapsulated into mesoporous silica nanoparticles (Pt-MSNPs) and the MSNPs were further surface modified with an anti-EpCAM aptamer (Pt-MSNP-E). Pt-MSNPs exhibited higher intracellular fluorescence compared to free BMPP-Pt, though both of them induced a similar degree of cell death via the apoptosis pathway, possibly via cell cycle arrest in the G1 phase. Anti-EpCAM aptamer modification was found to increase both cytotoxicity and intracellular fluorescence compared to unmodified MSNPs. Our study showed that EpCAM functionalized BMPP-Pt loaded MSNPs can efficiently internalize and induce apoptosis of cancer cells as well as show strong intracellular fluorescence. This study provides clues towards the development of a potential single compound based theranostic modality in future.