The development of aggregation-induced emission enhancement (AIEE) active nanoprobes without any synthetic complication for solution-state and organic thin-film transistor (OTFT)-based sensory applications is still a challenging task. In this study, the novel pyrene-incorporated Schiff base (5-phenyl-4-((pyren-1-ylmethylene)amino)-4H-1,2,4-triazole-3-thiol; PT2) with an AIEE property was synthesized via a one-pot reaction and was reported for detecting Zn 2+ and tyrosine in the solution state and OTFT. In the AIEE studies of PT2 (in CH 3 CN) at various water fractions (f w : 0− 97.5%), the existence of J-aggregation, crystalline changes, and nanofibers formation was confirmed by ultraviolet absorption/photoluminescence (UV/PL) spectroscopy, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and dynamiclight scattering (DLS) techniques. Similarly, PT2-based Zn 2+ detection and sensory reversibility with tyrosine were demonstrated by UV/PL studies with evidence related to crystalline/nanolevel changes in PXRD, SEM, TEM, AFM, and DLS data. Distinct decay profiles associated with the AIEE and sensory responses of PT2 were observed in time-resolved photoluminescence spectra. From the standard deviation and linear fittings of PL titrations, detection limits (LODs) of the Zn 2+ with PT2 and the tyrosine with PT2-Zn 2+ were estimated as 0.79 and 45 nM, respectively. High-resolution mass and 1 H NMR results confirmed 2:1 and 1:1 stoichiometry and binding sites of PT2-Zn 2+ -PT2* and tyrosine-Zn 2+ complexes. Moreover, the values of association constants determined by linear fittings were 4.205 × 10 −7 and 1.73 × 10 −8 M −2 , correspondingly. Optimization via the density functional theory disclosed the binding sites and suppression of twisted intramolecular charge transfer/photoinduced electron transfer (TICT/ PET) as well as the involvement of restricted intramolecular rotation in the AIEE and PET "ON-OFF-ON" mechanisms in the Zn 2+ and tyrosine sensors. Results from the B16−F10 cellular and zebrafish imaging of AIEE, Zn 2+ , and tyrosine sensors further attested the applicability of PT2 in biological samples. Finally, the PT2 and pentacene-incorporated OTFT devices were fabricated. The devices displayed more than 90% change in drain-source current when reacted with Zn 2+ with an LOD of 5.46 μM but showed no response to tyrosine, thereby confirming the reversibility. Moreover, the OTFT devices also demonstrated Zn 2+ ion detection in tap water and lake water samples.

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Temperature-dependent electroabsorption (E-A) spectra of methylammonium lead tri-iodide (MAPbI3) solid film, which result from the quadratic Stark effect of the exciton absorption band, have been analyzed with an integral method. The change in the electric dipole moment (Δμ) and polarizability (Δα) following exciton absorption was determined at each temperature; the absorption profile was separated into an exciton band and a continuum band caused by a transition from the valence band to the conduction band, and the position and the linewidth of the exciton absorption band were determined at each temperature. As the temperature decreased, a phase transition occurred from a tetragonal phase to an orthorhombic phase; the temperature dependence of Δμ and Δα differed greatly between the two phases. We have evaluated the exciton binding energy (E B) of MAPbI3 polycrystalline film with the following three methods: (1) fitting the temperature-dependent absorption profile; (2) fitting the temperature-dependent linewidth of the exciton absorption profile; and (3) fitting the photoluminescence intensity as a function of temperature. The E B values thus determined for samples fabricated with the same procedure are compared. Our estimated binding energies for an exciton of a MAPbI3 nanocrystalline film are also compared with those reported in the literature.

Electroabsorption (E-A) spectra of lead halide perovskites, that is, CH3NH3PbI3–x Br x (x = 0–3), which show large spectral shift depending on the ratio between iodine and bromide, have been measured. By analyzing E-A spectra with the integral method, spectral shape of the absorption spectra for the first exciton band and binding energy of exciton have been determined. Magnitudes of the change in electric dipole moment and molecular polarizability following excitation into the exciton state have been also evaluated in these perovskites. The binding energy of electron and hole in exciton of these materials as well as the magnitude of change in electric dipole moment following exciton absorption is roughly the same, suggesting that the difference of the photoenergy conversion in photovoltaic cells using these materials comes from the difference in light harvesting effect and difference in carrier mobility, not from the difference in carrier generation efficiency. The frequency-dependent third-order nonlinear susceptibility χ(3) has also been calculated, based on the E-A spectra.

Organic–inorganic lead halide perovskite nanocrystals have attracted much attention as promising materials for the development of solid-state light-emitting devices, but the existence of free or bound excitons or the formation of trap states remains under debate. We recorded the temperature-dependent electroabsorption (E-A) and electrophotoluminescence (E-PL) spectra, that is, electric-field-induced change in absorption and photoluminescence spectra, for methylammonium lead tribromide (MAPbBr3) colloidal perovskite nanocrystals, that is, quantum dots (QD), doped in a poly­(methyl methacrylate) film in the temperature range of 40–290 K. Based on the results, the binding energy of the exciton (electron–hole pair) was estimated. The exciton binding energy of QD of MAPbBr3 estimated from the absorption and E-A spectra (∼17 meV) is nearly the same as that of a MAPbBr3 polycrystalline thin solid film, while the exciton binding energy estimated from the temperature-dependent PL spectra (∼70 meV) is much greater than that estimated from the absorption profile. The frequency dependence of the E-A intensity observed at 40 and 290 K for the modulated applied electric field indicates a slow ion migration in nanocrystals, which follows the modulation of the applied electric field at a frequency less than 500 Hz. The observed E-A spectra were analyzed with an integral method on assuming the Stark effect; the magnitudes of the changes in electric dipole moment and polarizability following photoexcitation were determined at each temperature from 40 to 290 K. E-PL spectra show that the PL of QD of MAPbBr3 is quenched on the application of an external electric field; the extent of quenching is much greater for trap emission than for exciton emission. Exciton–phonon scattering, which is responsible for the line broadening of the PL spectra, is also discussed based on the temperature-dependent PL spectra.

In this work we demonstrate time-gated confocal fluorescence imaging on live cancer cells immunostained by antibody-conjugated silicon quantum dot nanoparticles (SiQD-NPs) and organic dyes, for simultaneous detection of two biological targets and removal of background autofluorescence. With almost all radiative recombinations occurring through oxide-related defect states located on the SiQD surface, the SiQD-NPs have very long photoluminescence lifetimes of about 25 μs, in contrast to the nanosecondrange lifetimes of other commonly used biological fluorophores. This drastic lifetime difference enables a time-gated imaging method here, in which the time-resolved photon distribution of each pixel of a fluorescence image is measured by using a time-correlated single-photon counting technique. Then, by integrating the photon histogram of each pixel over respective time windows, the long-lived component of the fluorescence image comprising only the fluorescence emitted from the SiQD-NPs is separated from all other short-lived signals resulting from the organic dyes and the cell endogenous luminescence. For instance, the membrane and nucleus of a single cancer cell or two types of cancer cells, immunostained with the SiQD-NPs and the organic dyes, respectively, can be clearly distinguished from each other by time-gating, which otherwise cannot be accomplished by conventional multiplexing due to spectral overlap in the wavelength domain.

Development of luminescent and nontoxic Pb-free perovskite quantum dots (PQDs) for quantification of toxic/nontoxic heavy metal ions has attracted much attention recently. In this paper, blue emissive Pb-free bare and poly(ethylenimine), oleic acid stabilized methylammonium tin tribromide quantum dots (MASnBr 3 QDs and PEI-OA-MASnBr 3 QDs) are developed via modified synthetic routes with fluorescent quantum yields of (Φ f ) of 8.7 and 14.6%, respectively. The particle size, structures, diffraction patterns, and surface potential of PQDs are investigated using a high-resolution transmission electron microscope (HR-TEM), powder X-ray diffraction (PXRD), dynamic light scattering (DLS), and zeta potential techniques. Photoluminescence (PL) investigations demonstrate agglomeration-mediated energy transfer at various precursor concentrations and water sensitivity of PQDs. At 20 μL precursor concentration in DMSO, both QDs exhibit diverse fluorescent quenching to Fe 3+ and Cr 6+ with linear regression between 1−500 μM and nanomolar detection limits (LODs). Estimated Stern−Volmer quenching constant values are on the order of 10 3 −10 4 M −1 higher than those of other ions. PL and time-resolved PL studies confirm involvement of dynamic and static quenching in quantification of Fe 3+ /Cr 6+ for MASnBr 3 QDs and PEI-OA-MASnBr 3 QDs, respectively. Agglomeration of PQDs, Sn 2+ /MA + cationic displacement by Fe 3+ /Cr 6+ , and the existence of metal-oxide/hydroxide layer above the surface of QDs are confirmed by HR-TEM, DLS, zeta potential, X-ray photoelectron spectroscopy, and energy-dispersive spectroscopy investigations and supported by the density functional theory optimization. Biocompatibility of PQDs is authenticated by the methyl thiazolyl tetrazolium assay and IC 50 interrogations with supporting results from time-dependent cellular imaging of Fe 3+ and Cr 6+ ions. Individual titrations of PQDs with Fe 3+ and Cr 6+ in tap, lake, and seawater samples display linear behavior with micro/nanomolar LODs. Fe 3+ and Cr 6+ in spiked real water sample experiments show exceptional PL recoveries (>100%), which agree with the inductively coupled plasma-mass analysis.

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