An incisively designed notable aggregation-induced emission enhancement (AIEE) active fluorescence probe, 1-(2hydroxynaphthylmethylene)-2-(3-methoxy-2-hydroxybenzylidene) hydrazine (L), was synthesized via straightforward reaction from inexpensive reagents. It exhibited rapid response, superb selectivity, and swift sensitivity toward Zn 2+ based on its promising CHEF/AIEE feature. L not only can sense Zn 2+ through sharp colorimetric and selective turn-on fluorescence responses in DMF/H 2 O (9:1, v/v) medium, but also can distinguish between its significant AIEE activity in high water ratio and Zn 2+ triggered AIEE activity through individual emission signals. Intriguingly, the AIEE properties of L may improve its impact. The molecules of L are aggregated into ordered one-dimensional rod-shaped microcrystals that show an obvious optical waveguide effect. Job's plot from UV−vis absorption revealed the formation of L-Zn 2+ complex with 1:1 stoichiometry. When bound with Zn 2+ in 1:1 mode, enhanced turn-on emission was observed via chelation enhanced fluorescence through sensor complex (L-Zn) formation and excess addition of Zn 2+ , a vivid enhancement of fluorescence intensity over manifold through aggregate formation was observed. The entire process takes ∼5 s, i.e., faster response time. The probe can detect Zn 2+ as low as 1.1 × 10 −7 M. The AIEE mechanism of L and Zn 2+ triggered AIEE mechanism were well established from fluorescence anisotropy, DLS, SEM, optical fluorescence microscope, time-resolved photoluminescence, and fluorescence reversibility study by adding Zn 2+ and EDTA sequentially. Furthermore, the proposed analytical system with clear AIEE mechanism demonstrates a potential outlook for the on-site practical applications.

A pyrene based fluorescent probe, 3-methoxy-2-((pyren-2yl-imino)methyl)phenol (HL), was synthesized via simple one-pot reaction from inexpensive reagents. It exhibited high sensitivity and selectivity toward Al(3+) over other relevant metal ions and also displayed novel aggregation-induced emission enhancement (AIEE) characteristics in its aggregate/solid state. When bound with Al(3+) in 1:1 mode, a significant fluorescence enhancement with a turn-on ratio of over ∼200-fold was triggered via chelation-enhanced fluorescence through sensor complex (Al-L) formation, and amusingly excess addition of Al(3+), dramatic enhancement of fluorescence intensity over manifold through aggregate formation was observed. The 1:1 stoichiometry of the sensor complex (Al-L) was calculated from Job's plot based on UV-vis absorption titration. In addition, the binding site of sensor complex (Al-L) was well-established from the (1)H NMR titrations and also supported by the fluorescence reversibility by adding Al(3+) and EDTA sequentially. Intriguingly, the AIEE properties of HL may improve its impact and studied in CH3CN-H2O mixtures at high water content. To gain insight into the AIEE mechanism of the HL, the size and growth process of particles in different volume percentage of water and acetonitrile mixture were studied using time-resolved photoluminescence, dynamic light scattering, optical microscope, and scanning electron microscope. The molecules of HL are aggregated into ordered one-dimensional rod-shaped microcrystals that show obvious optical waveguide effect.

Optical emission from a luminogen in solid state is generally red shifted with respect to its solution phase emission. However, in our present study, we report exceptionally large blue shifted enhanced emission from aggregated hydrosol of 4,4'-bis(diethylamino)benzophenone (BZP) compared to its solution phase emission in any good solvent. This exceptional blue emission from aggregated structure of BZP arises from its locally excited states with the concomitant suppression of twisted intramolecular charge transfer (TICT) motion. This is known as aggregation induced locally excited (AILE) state emission. A broad red shifted emission is also observed in case of larger aggregated structure of BZP and it originates from the excited intramolecular charge transfer (ICT) state of planar BZP. Morphology of the aggregated BZP is also studied by scanning electron microscopy and optical microscopy. This AILE emission of the luminogen is used for sensing glucose in aqueous solution at very low concentration. The quenching of AILE in presence of glucose has been explained due to hydrogen bonded complexation between glucose and BZP molecule present at the surface of the aggregated structure and is responsible for crystal softening, i.e. loosening of crystal packing.

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Bathophenanthroline (BA) microstructures of various morphologies have been synthesized using a reprecipitation method. The morphologies of the particles are characterized using optical and scanning electron microscopy (SEM) methods. An aqueous dispersion of BA microstructures shows aggregation induced emission enhancement (AIEE) compared to BA in a good solvent, THF. This luminescent property of aggregated BA hydrosol is used for the selective detection of trace amounts of mercury ion (Hg(2+)) in water. It is observed that Hg(2+) ions can quench the photoluminescence (PL) intensity of BA aggregates even at very low concentrations, compared to other heavy metal ions e.g. nickel (Ni(2+)), manganese (Mn(2+)), cadmium (Cd(2+)), cobalt (Co(2+)), copper (Cu(2+)), ferrous (Fe(2+)) and zinc (Zn(2+)). This strong fluorescence quenching of aggregated BA in the presence of Hg(2+) ions has been explained as a complex interplay between the ground state complexation between BA and Hg(2+) ions and external heavy atom induced perturbation by Hg(2+) ions on the excited states of the fluorophore BA.