AIE active polymers for biological applications.

The discovery of aggregation-induced emission (AIE) phenomenon, significantly altered the understanding of the scientific world about the luminophore aggregation. Polymers with AIE features have recently emerged as promising materials with wide range of applications in optoelectronics devices, chemosensors, bioimaging, cancer theranostics and drug delivery. By introducing the AIE active molecule into the polymer structure, novel materials encompassing the characteristics properties of both the functional materials such as excellent brightness, versatile structure modification, high biocompatibility, exceptional stability and facile processability are achieved. This chapter presents the advances in synthetic design as well as potential biological applications of AIE active polymers, beginning with a brief introduction to the AIE phenomenon. The versatile synthetic route, easier functionalization, and light up feature of the AIE active polymers offer direct visualization of the physiological processes within or outside the living organisms. This chapter also precisely describes the photodynamic therapy/photothermal therapy (PDT/PTT) with up-to-date advancement of AIE active polymer and their emerging applications in biomedical field. The AIE active Photosensitizers (PSs) are much more efficient in singlet oxygen (1O2) production than their small molecule AIE active PSs due to their enhanced inter system crossing (ISC) process and improved light-harvesting ability. Additionally, the present chapter aims to focus on all recent AIE active polymers for drug screening and drug delivery. The AIE active polymer often shows decent drug loading capacity, high stability and good biocompatibility comprising image guided drug monitoring features. Lastly, the concluding discussion reveals the future prospective of the AIE active polymers.

Effects of incorporating regioisomers and flexible rotors to direct aggregation induced emission to achieve stimuli-responsive luminogens, security inks and chemical warfare agent sensors.

Efficient transformation of ACQ materials to AIE luminogens using simple design principles of positional isomerization and C-C bond exclusion is presented here. Consequently, the bond link, position and packing influence the photophysical properties that can be utilized in erasable secret inks, pressure sensors and chemical warfare sensors.

Stepwise elucidation of fluorescence based sensing mechanisms considering picric acid as a model analyte.

In most of the sensing systems, specific detection mechanisms are involved during the detection process for a certain analyte irrespective of probes. However, unlike that of various sensing analytes, the detection of the highly toxic and explosive picric acid (PA) analyte was found to involve significant types of distinct sensing mechanisms depending on the nature of probes. Moreover, in the past five years, apart from the plethora of fluorescent probes designed, a number of unique organic small molecules and polymers have been strategically developed at our laboratory for the detection of PA, wherein the involvement of several diverse mechanisms along with a few new mechanisms depending on the electronic and photophysical properties of the probes has been unveiled. This involvement of several distinct mechanisms for the detection of PA motivated us to compile a step-by-step guide for the elucidation of the fluorescence sensing mechanism by taking PA as a model analyte. This "tutorial review" summarizes all the common sensing mechanisms involved for the detection of PA hitherto and provides a step-by-step guide to design experiments for the elucidation of sensing mechanisms for any newly designed sensing system. In addition to the appropriate classification of mechanisms involved for the fluorescence sensing of PA using various fluorescent systems developed at our laboratory, this tutorial review also includes most other possible mechanistic approaches studied previously. The present tutorial also provides a very unique method of a flow chart, which could help readers to elucidate the likely sensing mechanism via stepwise experimental and theoretical studies. Apart from the elucidation of the sensing mechanism for PA, this review presents an easy and distinct approach for the identification of all the involved mechanisms that would be of primary concern in the detection process of any analyte and could accurately help researchers in the easy and quick elucidation of sensing mechanisms in any kind of fluorophore-analyte system.

Inner Filter Effect and Resonance Energy Transfer Based Attogram Level Detection of Nitroexplosive Picric Acid Using Dual Emitting Cationic Conjugated Polyfluorene.

A novel conjugated cationic polyfluorene (polyelectrolyte) derivative, PFBT, was developed by means of simple and cost-effective oxidative coupling polymerization method. PFBT displayed dual state emission in dimethyl sulfoxide (DMSO) as well as in water, a characteristic phenomenon of polyfluorene homopolymers, and tested for nitroexplosive analytes detection to observe a remarkable fluorescence quenching response for picric acid (PA) in the both solvents. The polymer PFBT demonstrated substantial selectivity and ultrasensitivity toward nitroexplosive PA in both the solvents (DMSO and H2O) with exceptional quenching constant values of 2.69 × 104 and 2.18 × 105 M-1 and a ultralow limit of detection of 92.7 nM (21.23 ppb) and 0.19 nM (43.53 ppt) in respective solvents. Furthermore, economical portable test strip devices were prepared for easy and fast on-site PA sensing, which can detect up to 0.22 ag level of PA. PA sensing in vapor phase was also established, that could detect up to 42.6 ppb level of PA vapors. Interestingly, the mechanism of sensing in DMSO solvent was attributed to substantial inner filter effect and photoinduced electron transfer, while in H2O the sensing occurs via possible resonance energy transfer and photoinduced electron transfer, which is exceptional and not reported earlier for a single probe.

Receptor-Free Detection of Picric Acid: A New Structural Approach for Designing Aggregation-Induced Emission Probes.

A pristine aggregation-induced enhanced emission (AIEE) active monomer 2,5-bis(( E)-4-bromostyryl)-3,4-diphenylthiophene (TPBZ) and its copolymer (PFTPBZ) with 9,9-dioctylfluorene-2,7-diboronic acid bis(1,3-propandiol) ester have been synthesized via Suzuki coupling polymerization. PFTPBZ that is devoid of any receptor showed AIEE property and demonstrated excellent and selective fluorometric recognition of 2,4,6-trinitrotoluene (TNT) in aggregated state (aqueous medium) and picric acid (PA) in aggregated state and solution state (organic solvent) as well as in vapor phase via PFTPBZ dip-coated Whatman filter paper on a solid-phase platform in 1.86 ng level (naked eye). Limit of detection (LOD) for TNT in 95% water fraction ( fw) was 53.74 × 10-6 M, and at 40% fw, it was 14.26 × 10-7 M. PA detection in tetrahydrofuran solution was possible with a LOD of 28.16 × 10-7 M, 95% fw with LOD of 10.47 × 10-6 M, and in 40% fw with LOD of 47.39 × 10-8 M. As a unique example of structural design, the probe PFTPBZ surprisingly possesses no receptor, yet remarkably high selectivity was achieved via Förster resonance energy transfer (FRET) and photoinduced electron transfer from the copolymer PFTPBZ to PA and TNT. Detection of PA in the presence of various metal analytes and inorganic acids in real water samples (lakes, rivers, and sea water) was also demonstrated using this concept of receptor-free conjugated polymer probe.