Debabrata Jana

Planar–rotor architecture based pyrene–vinyl–tetraphenylethylene conjugated systems: photophysical properties and aggregation behavior

Four pyrene-vinyl-tetraphenylethylene based conjugated materials were synthesized and characterized by FT-IR, NMR, and mass spectroscopy. The photophysical (including absorption, fluorescence, and fluorescence lifetime) and aggregation properties in tetrahydrofuran were investigated. The photophysical and aggregation behavior depends on the spacer, substituent, and also the architecture (mono or tetra-branched) of the molecule. The vinyl spacer mono-branched compound is aggregation induced emission (AIE) active (αAIE = ∼6). Vinyl spacer tetra-branched compounds are AIE inactive, but their emitting efficiency is good in both solution (Φfl = 63%) phase and in the aggregated state (Φfl = 43%). Phenylvinyl spacer tetra-branched compounds emit light strongly in solution (Φfl = 92%), but not in the aggregated state (Φfl = 8%). They are shown to be thermally stable and emit light in the green region (500-550 nm). The results of cyclic voltammetry measurements of these materials showed irreversible oxidation waves, and have high HOMO energy levels (-5.66 to -5.53 eV).

Functionalized chitosan with self-assembly induced and subcellular localization-dependent fluorescence ‘switch on’ property

Chitosan-based polymers are commonly used as drug delivery carriers and for functional modification of nanoparticle/polymers. Herein, we report a functional chitosan oligosaccharide with a self-assembly-induced fluorescence ‘switch on’ property, and that also exhibits a similar type fluorescence ‘off’ to ‘on’ state via subcellular localization. Specifically, chitosan oligosaccharide was conjugated with aggregation induced emission (AIE) active tetraphenylethene (TPE) and lipophilic–cationic triphenylphosphonium (TPP) molecules. The resultant functional chitosan self-assembles into 50–200 nm particles, whereby TPE offers a self-assembly induced fluorescence ‘switch on’ property and TPP offers cell uptake via lipophilic–cationic surface properties. The self-assembled chitosan nanoparticle enters into the cell predominately by lipid-raft endocytosis and exhibit a fluorescence ‘off’ to ‘on’ state upon localization at the lysozome. We have shown that adjustment of the number of TPP/TPE molecules bound to each chitosan is critical for the self-assembly induced fluorescence ‘switch on’ property and the subcellular localization-dependent fluorescence ‘off’ to ‘on’ state performance. Other fluorescence ‘switch on’ type sub-cellular imaging probe could be designed with appropriate functional modification of chitosan oligosaccharide or similar macromolecules.

Electron donating group stimulated aggregation induced emission enhancement of oligophenylenevinylene-cored luminogens†

Three new oligophenylenevinylene (OligoPV)-cored luminogens were synthesized by utilizing the Suzuki coupling/Buchwald–Hartwig amination reaction and their aggregation-induced emission properties have been studied. Out of three, two are aggregation-induced emission enhancement (AIEE)-active molecules: weakly fluorescent in solution, while highly emissive in the aggregation state. The presence of the OligoPV core has turned an aggregation-caused quenching (ACQ) luminophore into an AIEE one. They show excellent solubility in common organic solvents, emit light in the green region (500–516 nm) and have high thermal stability.