An Isothiazolanthrone-Based Self-Assembling Anticancer Color-Changing Dye for Concurrent Imaging and Monitoring of Cell Viability.

We report the photophysical properties, self-assembly and biological evaluation of an isothiazolanthrone-based dye, 7-amino-6H-anthra[9,1-cd]isothiazol-6-one (AAT), which reveals anticancer properties and can be potentially used as dye for monitoring cell viability. The solvent-dependent photophysical studies suggest that the emission of AAT is sensitive to environment polarity due to which interesting changes in the colored emission may be observed owing to the charge transfer (CT) processes. AAT also self-assembles to tree-like branched morphologies and produce, a greenish emission inside the cells when imaged after short interval (15 mins) of incubation while a red fluorescence could be noted after 24 h. Interestingly, AAT also produce differential emission inside mouse normal cells as compared to its cancer cell lines since it possess anticancer activity. The experimental observations were also validated theoretically via computational modeling.

A new aggregation induced emission enhancement (AIEE) dye which self-assembles to panchromatic fluorescent flowers and has application in sensing dichromate ions.

We report for the very first time the crystal structure and self-assembly of a new aggregation-induced emission enhancement (AIEE) dye 4-(5-methoxythiazolo[4,5-b]pyridin-2-yl)-N,N-dimethylaniline (TPA) and its application in sensing dichromate ions. TPA reveals cyan blue emission under UV and visible light. The self-assembly properties of TPA were studied extensively by scanning electron microscopy (SEM) which revealed the formation of beautiful flower-like morphologies. These structures revealed both green and red fluorescence under FITC and rhodamine filters respectively when observed through fluorescence microscopy connoting the panchromatic emission properties of TPA from blue to red. The interactions which cause self-assembled structure formation in TPA were also validated theoretically using density functional theory (DFT) calculations. Crystal and molecular structure analysis of TPA was carried out via single-crystal X-ray diffraction to visualize the intermolecular interactions occurring in the solid-state and to study the structure-photophysical property relationship in the aggregated state. The photophysical properties of TPA were also studied extensively by UV-visible and fluorescence spectroscopy and its quantum yield and fluorescence lifetime were calculated by time-correlated single-photon counting (TCSPC). Interestingly, TPA could efficiently sense dichromate (Cr2O72-) ions in an acidic medium and an interesting morphological transition from a fluorescent flower to non-fluorescent disassembled structures could also be observed. The limit of detection of TPA for Cr2O72- ions was found to be as low as 5.5 nM, suggesting its exceptional sensitivity. More importantly, TPA could selectively sense Cr2O72- ions in real water samples even in the presence of other metal ions routinely present in polluted water, hence making it practically useful for water quality monitoring.

Introduction to aggregation induced emission (AIE) materials.

Idea of introducing aggregation-induced emission (AIE) fundamentally altered the scientific community's perception of classical photophysical processes. Many exciting new possibilities have been coming into light due to the emergence of AIE, such as ability of rapid detection and in analyzing variety of bioactive substances required to monitor the complexed biological processes. This also became a handy tool in elucidating the essential physiological and pathological behaviors of organisms. AIE luminogens (AIEgens) are luminous substances that are either weakly or non-emissive in organic solvents or hydrophobic environment alone, but it gives strong emissive when aggregated along with transforming polarities upon aggregation. Owing to the their outstanding advantages such as rapid turn on/off of high brightness emission, big Stokes shift, excellent photostability, and strong biocompatibility AIEgens have become first choice among bio-inspired probes in biomedicine. In the view of providing basic information on AIE, this chapter give a brief overview of aggregation-caused quenching (ACQ) phenomenon, approaches to transform ACQ to AIE phenomenon, photo-physics of AIE phenomenon, followed by known and reportedly novel AIE active molecules and their biomedical applications.

A hybrid upconversion nanoprobe for ratiometric detection of aliphatic biogenic amines in aqueous medium.

We fabricated an inorganic-organic hybrid upconversion nanoprobe for the ratiometric detection of aliphatic biogenic amines in water. The hybrid nanoprobe comprises a thiophene-based acceptor-π-donor-π-acceptor organic fluorescent dye, TDPM, and near-infrared light-absorbing upconversion nanoparticles (UCNPs). The organic dye was loaded into a mesoporous silica-coated UCNP (UCNP@mSiO2) matrix to circumvent the issues of water insolubility and higher energy excitation. Yb3+ and Tm3+-doped UCNPs exhibited dual emission bands at 475 and 645 nm upon excitation with a 980 nm laser. The significant spectral overlap between the absorption and the emission bands of TDPM and UCNPs, respectively, at 475 nm led to resonance energy transfer (RET) from the UCNPs to TDPM resulting in the quenching of the UCNP emission. In contrast, 'turn-on' emission was noticeable with the addition of aliphatic biogenic amines due to an inhibition of the RET. The emission at 645 nm remained unaffected during the energy transfer process making the hybrid probe a versatile platform for the ratiometric detection of different aliphatic biogenic amines. Furthermore, we explored the sensing of aliphatic biogenic amines in adulterated milk and rotten fish. The unique material attributes demonstrated in the current study hold promise for further development of real-time sensors and switches based on hybrid upconversion nanoprobes.

Morphological and Optical Engineering for High-Performance Polymer Solar Cells.

We demonstrate morphological and optical engineering by using processing additives and optical spacers for polymer solar cells. Among various processing additives, introduction of diphenyl ether (DPE) into the active layer results in the smoothest surface roughness with uniform and well-distributed donor/acceptor domains, and the device with DPE shows the highest device efficiency of 10.22% due to enhanced charge collection efficiency and minimized recombination loss. Additional ZnO optical spacers on the active layer controls the distribution of the electric field in the whole device and enhances the light absorption within the active layer, thereby improving device efficiency up to 10.81%.

A smart photosensitizer based on a red emitting solution processable porous polymer: generation of reactive oxygen species.

A novel approach for the fabrication of a solution processable conjugated porous organic polymer (CzBDP) involving a flexible core composed of carbazole and boron dipyrromethene was developed. The red emitting soluble polymer was found to be an excellent probe for the generation of both singlet oxygen and superoxide anion radicals under visible light irradiation.

Redox-active, pyrene-based pristine porous organic polymers for efficient energy storage with exceptional cyclic stability.

A novel class of pyrene-based conjugated porous organic polymers having an N-containing network was developed by employing Buchwald-Hartwig coupling for supercapacitor energy storage. The pristine polymer was found to exhibit a specific capacitance of 456 F g-1 at 0.5 A g-1 current density with excellent long-term cyclic stability.

Microporous organic polymers involving thiadiazolopyridine for high and selective uptake of greenhouse gases at low pressure.

A new core of [1,2,5]-thiadiazolo-[3,4-c]-pyridine was employed for the fabrication of microporous organic polymers exhibiting a very high CO2 uptake of 5.8 mmol g-1 (25.5 wt%) at 273 K and 1 bar. The presence of CO2-philic active sites and microporosity confer the high uptake and superior selectivity (61) towards CO2 over N2.

A soluble conjugated porous organic polymer: efficient white light emission in solution, nanoparticles, gel and transparent thin film.

A tetraphenylcyclopentadiene based multifunctional, solution processable, fluorescent, ultramicroporous polymer exhibiting high hydrogen uptake was employed for encapsulation of dyes to obtain enhanced white light emission in solution, nanoparticles, gel and transparent thin film. Hybrid nanoparticles showed a quantum yield of 35% with a high color rendering index.

Multifunctional Porous Organic Polymers: Tuning of Porosity, CO2, and H2 Storage and Visible-Light-Driven Photocatalysis.

A series of porous organic polymers (POPs) were fabricated based on a boron dipyrromethene (BODIPY) core. The variation of the substituents in the BODIPY core and the fine-tuning of the Sonogashira polycondenzation reaction with 1,3,5-triethynylbenzene led to the formation of POPs with a wide range of surface area and porosity. A 10-fold increase in surface area from 73 m2 g-1 in BDT1a polymer to 1010 m2 g-1 in BDT3 was obtained. Simultaneously, the porosity was changed from mesoporous to ultramicroporous. The surface area of BDT3 turned out to be the highest reported so far for BODIPY-based POPs. Molecular dynamics simulation coupled with Grand Canonical Monte Carlo simulations revealed the effect of substituents alkyl groups and rigidity of the core structures on the surface properties of the POPs. Detailed gas adsorption studies of the polymers revealed a high uptake of CO2 and H2. The highest uptake capacity of 16.5 wt % for CO2 at 273 K and 2.2 wt % for H2 at 77 K was observed for BDT3 at 1 bar pressure. The isosteric heat of adsorption (Qst) of BDT3 for CO2 was found to be as high as 30.6 kJ mol-1. Electron paramagnetic resonance studies revealed the generation of singlet oxygen upon photoexcitation of these polymers. The BODIPY-based POPs turned out to be excellent catalysts for visible-light-driven photo-oxidation of thioanisole. The present study establishes BODIPY-based POPs as a new class of multifunctional materials.

Conjugated Polymer Nanoparticle-Triplet Emitter Hybrids in Aqueous Dispersion: Fabrication and Fluorescence Quenching Behavior.

Conjugated polymer nanoparticles based on poly[9,9-bis(2-ethylhexyl)fluorene] and poly[N-(2,4,6-trimethylphenyl)-N,N-diphenylamine)-4,4'-diyl] are fabricated using anionic surfactant sodium dodecylsulphate in water by miniemulsion technique. Average diameters of polyfluorene and polytriarylamine nanoparticles range from 70 to 100 and 100 to 140 nm, respectively. The surface of the nanoparticles is decorated with triplet emitting dye, tris(2,2'-bipyridyl)ruthenium(II) chloride. Intriguing photophysics of aqueous dispersions of these hybrid nanoparticles is investigated. Nearly 50% quenching of fluorescence is observed in the case of dye-coated polyfluorene nanoparticles; excitation energy transfer is found to be the dominant quenching mechanism. On the other hand, nearly complete quenching of emission is noticed in polytriarylamine nanoparticle-dye hybrids. It is proposed that the excited state electron transfer from the electron-rich polytriarylamine donor polymer to Ru complex leads to the complete quenching of emission of polytriarylamine nanoparticles. The current study offers promising avenues for developing aqueous solution processed-electroluminescent devices involving a conjugated polymer nanoparticle host and Ru or Ir-based triplet emitting dye as the guest.