Parvej Alam

Facile tuning of the aggregation-induced emission wavelength in a common framework of a cyclometalated iridium(III) complex: micellar encapsulated probe in cellular imaging

A simple synthetic protocol involving two steps was developed for the syntheses of a series of monocyclometalated iridium(III) complexes. Initially, an intermediate, [IrHCl[(o-C6H3X)P(Ar)x−(PArxRy)2] [A (i, j, k, l)], six-coordinated iridium(III) complex involving a 4-membered chelate was isolated. Then, it was transformed into a monocyclometalated iridium(III) complex, [(C^N)Ir(PArx−1Ry)2(Cl(H)] (1–12), by the replacement of the 4-membered chelates with 5-membered cyclometalates. The intermediates and the complexes were structurally characterized by FTIR, 1H, 13C and 31P NMR spectroscopies. Octahedral coordination for Ir(III) in 2, 8 and 9 was established by single crystal X-ray diffraction. Photo-physical experiments and quantum chemical calculations revealed a mixed LC/MLCT/LLCT nature for the lowest excited states of all these complexes that emit bright light in the solid state. Fine tuning of the emission wavelength throughout the visible range was achieved by suitable combinations of chromophoric cyclometalates and non-chromophoric aryl phosphine ligands. More interestingly, all the studied complexes were found to be aggregation-induced emission (AIE) active. One of these AIE active materials (6) was encapsulated inside polymeric micelles that inhibit the macroscopic precipitation of the aggregated complex, <200 nm water-soluble particle exhibiting a strong emission. These colloidal luminescent particles were used as a potential non-toxic bio-imaging probe.

Highly sensitive explosive sensing by “aggregation induced phosphorescence” active cyclometalated iridium(III) complexes

Two phosphorescent complexes [Ir(o-CHOppy)(PPh3)2(H)Cl] (1) and [Ir(ppy)(PPh3)2(H)Cl] (2) exhibiting ‘aggregation induced phosphorescent emission (AIPE)’ properties have been found to be very sensitive to the detection of picric acid (PA). The detection limit for PA has been checked and was found to be 264 nM and 65 nM for complexes 1 and 2, respectively.

Rare observation of ‘aggregation induced emission’ in cyclometalated platinum(II) complexes and their biological activities

Three strong solid state emissive cyclometalated platinum(II) complexes [Pt(C⁁N) (CH⁁N) (Cl)] (1) (C⁁N/CH⁁N = 2-phenylpyridine, C⁁N = bidentate and CH⁁N = monodentate), [Pt(C⁁N) (P⁁P)]Cl [P⁁P = bis(diphenylphosphino)ethane (2) and cis-1,2-bis(diphenylphosphino)ethene (3)] were reported. These were identified as ‘Aggregation Induced Emission (AIE)’ active complexes based on controlled experiments. Cytotoxicity and cell imaging have been studied for the complex 2.

‘Aggregation induced emission’ active iridium(III) complexes with applications in mitochondrial staining

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.

Simple ratiometric push–pull with an ‘aggregation induced enhanced emission’ active pyrene derivative: a multifunctional and highly sensitive fluorescent sensor

A simple ratiometric push–pull and ‘aggregation-induced emission enhancement (AIEE)’ active pyrene based compound, 2-(pyren-1-yl)pyridine (L), was synthesized and characterized by 1H NMR, HRMS and SXRD. The synthesized compound was established as a highly selective and sensitive multi-functional sensor that exhibits a ratiometric fluorescent response, detecting picric acid, H+ and Al3+ [observed sensitivity: 56 nM (12.82 ppb) for picric acid; 2.4 nM (0.27 ppb) for trifluroacetic acid; 2.3 nM (0.86 ppb) for Al3+]. Both L and LH+ have shown emission tuning ability on varying their concentration in solution. Computational calculations (DFT and TD-DFT) have been correlated with the experimental spectroscopic properties.

Dual emission and multi-stimuli-response in iridium(III) complexes with aggregation-induced enhanced emission: applications for quantitative CO2 detection

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.

Induced Aggregation of AIE‐Active Mono‐Cyclometalated Ir(III) Complex into Supramolecular Branched Wires for Light‐Emitting Diodes

Aggregation-induced emission (AIE) is commonly observed in irregular bulk form. Herein, unique aggregation properties of an AIE-active complex into branched supramolecular wires are reported for the first time. Mono-cyclometalated Ir(III) complex shows in-plane J-aggregation at the air-water interface owing to the restriction of intramolecular vibration of bidentate phenylpyridinato and intramolecular rotations of monodentate triphenylphosphine ligands at air-water interface. As a consequence, a large enhancement of luminescence comparable to the solid state is obtained from the monolayers of supramolecular wires. This unique feature is utilized for the fabrication of light-emitting diodes with low threshold voltage using supramolecular wires as active layer. This study opens up the need of ordered assembly of AIE complexes to achieve optimal luminescence characteristics.

Encapsulation of multi-stimuli AIE active platinum(II) complex: a facile and dry approach for luminescent mesoporous silica

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.

‘Aggregation induced phosphorescence’ active iridium(III) complexes for integrated sensing and inhibition of bacterial growth in aqueous solution

The present study attempts to develop a sensitive method to utilize ‘aggregation induced phosphorescence (AIP)’ active iridium(III) complexes as potential agents for “integrated” sensing and inhibition of bacterial growth in aqueous systems. The utilization of iridium(III) complexes for microbial detection in bodies of water has been demonstrated using Escherichia coli (E. coli) as a representative bacterial strain. The tested iridium(III) complexes also exhibited antibacterial properties against representative Gram positive and Gram negative bacterial strains with minimum inhibitory concentration (MIC) values of 4 and 8 μg mL−1, respectively. Microscopic observations indicated that these complexes could penetrate into the bacterial cells and result in subsequent cell death. Preliminary mechanistic studies showed that the DNA binding ability of the iridium(III) complexes is responsible for their antibacterial properties. The observed “dual” role in detection as well as inhibition of bacterial growth makes this study highly promising and encouraging for the exploration of the applicability of other less expensive metal complexes for monitoring and controlling the bacterial levels in drinking and sea water systems at a commercial level.