Shift Of Photoluminescence Research Articles

Halochromism of 2-indolinone fluorophore based on the deprotonation of an acidic C–H bond

Abstract We disclosed a new halochromic fluorescent dye based on the deprotonation from an acidic C–H bond. The dye consisting of a 2-indolinone skeleton and a benzothiazole ring exhibited an obvious red shift in its photoluminescence spectra in response to the presence of bases. Structural analyses with 1H NMR measurements and theoretical calculations suggested that the π-conjugated system of the dye was expanded by the deprotonation of the acidic C–H bond on the 2-indolinone skeleton. This structural change contributes to the red shift of photoluminescence and accelerates the radiative decay from the excited state.

Design and synthesis of dicyanoethylene derivatives functionalized with carbazole possessing the properties of obvious aggregation-induced emission and reversible high-contrast mechanofluorochromism

This study devotes to the design, preparation, and examination of two novel D-A structured molecules, designated as CCEDBF and BCCEDBF, which are derived from carbazole unit, dicyanoethylene segment, and dibenzofuran unit. The distinctive D-A molecular architectures and highly twisted spatial configurations of these compounds facilitate pronounced intramolecular charge transfer (ICT) while also imparting robust solid-state luminescence, exhibiting emission efficiencies of 0.518 and 0.739, respectively, and notable aggregation-induced emission (AIE) with AIE factors of 43 and 30. Significantly, both CCEDBF and BCCEDBF demonstrate reversible mechanofluorochromic (MFC) behavior characterized by high fluorescence contrast. Mechanical grinding of the initial powders results in a shift in their emission colors, transitioning from green and yellow-green to yellow and orange-red, respectively, alongside a corresponding shift in emission peaks from 525 nm to 536 nm–558 nm and 597 nm. Powder X-ray diffraction (PXRD) examination of the initially synthesized, mechanically processed, and vaporized samples reveals that the observed fluorescence color change is due to a structural transformation between ordered crystalline and disordered amorphous configurations induced by the application of the external force. The red shift in photoluminescence (PL) spectra post-grinding is attributed to a reduced band gap, driven by factors such as extended π-conjugation length, enhanced planar intramolecular charge transfer (PICT) effect, strengthened π-π interactions and exciton coupling, as well as the increase in the orbitals overlap between neighboring molecular. Moreover, the presence or absence of tert-butyl substituents attaching to the 3- and 6-positions of the carbazole units significantly impacts the photophysical properties of these materials.

Reversible photoluminescence shift in imidazolium l-tartrate crystal triggered by acoustic shock waves

Abstract Imidazolium l-tartrate crystal has been grown by employing the slow evaporation technique using de-ionized water as the solvent. An impact study on the exposure of shock pulses on the surface of the material has been carried out and the influence of shock waves on its photo luminance has been investigated. In the present work, in order to carry out the experiment, a shock wave of Mach number 1.5 has been utilized which has been generated by a semi-automated Reddy Tube. Imidazolium tartrate crystal is made into a fine powder and split into four identical parts to be used for further characterization. A series of shock waves such as 25, 50, and 75 are impacted on the respective samples while keeping one of the samples as the control. The powder X-ray diffraction analysis reveals that the observed increase in peak intensity and peak shifting is due to the increase in the number of shock pulses from 25 to 75. FTIR is performed to analyze the presence of functional groups in the material before and after shock exposure. Photoluminescence measurements are also carried out for the pre- and post-shocked samples to determine the nature of optical emission with respect to various shock pulse counts. The above experimental analyzes confirm that the title sample undergoes a reversible photoluminescence shift induced by shock waves.

Wide-Range and Multistate Work Functions of Organometallic Halide Perovskite Films Regulated by Ferroelectric Substrates.

Work function of organometallic halide perovskite (OHP) films is one of the most crucial photoelectric properties, which dominates the carrier dynamics in OHP-based devices. Despite surface treatments by additives being widely used to promote crystallization and passivate defects in OHP films, these chemical strategies for modulation of work functions face two trade-offs: homogeneity on the surface versus along the thickness; the range versus the accuracy of modulation. Herein, by using ferroelectric substrates of uniform polarization and subnanometer roughness, homogeneous CH3NH3PbI3 films are fabricated with five states of work functions with large spanning (∼0.8 eV) and high precision (sd ∼ 0.01 eV). We reveal that the ferroelectric polarizations and the smooth surfaces regulate CH3NH3+ orientations and suppress distortions of PbI6 octahedrons. The wide-range and multistate work functions originate from the ordered CH3NH3+ orientations and PbI6 octahedrons, which result in intensity enhancements and wavelength shifts in photoluminescence with a 30-fold increase of photoexcited carrier lifetime.

Effects of donor substituents on the conformational heterogeneity, photophysical, mechanochromic and electroluminescent properties of the donor-substituted fluorine-containing triphenylpyrimidines

Three derivatives of fluorinated triphenylpyrimidine with the attached carbazole, phenothiazine, or acridan donor moieties are synthesized by Buchwald-Hartwig reactions. The impact of the donor units on emissive and other properties of the compounds is reported. The compounds exhibit excellent thermal stability, competitive photophysical phenomena such as room temperature phosphorescence (RTP) appearing when compounds are molecularly dispersed in the rigid polymer matrix and thermally activated delayed fluorescence (TADF). The compounds with carbazole and phenothiazine donor moieties show the manifestation of triplet–triplet annihilation in the electroluminescence when used as emitters in organic light-emitting diodes (OLEDs). The phenothiazine-containing compound exhibit dual photoluminescence with the blue-shifted peak corresponding to the quasi-axial conformer and a red-shifted peak to the quasi-equatorial conformer. This derivative shows reversible shifts of emission spectra exceeding 100 nm due to the stable (at least 4 cycles) mechanochromic luminescence under the application of external stimuli. After grinding the emission intensity maximum is observed at 555 nm, after fuming at. ca 448 nm and after melting at 555 nm. The photoluminescence shifts and ON/OFF delayed fluorescence of the phenothiazine-based emitter occur due to the alteration between the crystalline and amorphous states. Optimization of the device structure allows to control the charge balance resulting in external quantum efficiency of up to 5.7 % observed for the OLED based on the phenothiazine-based emitter. This compound also shows the biggest response to the presence of oxygen acting as the quencher of triplet excited energy. The film of the compound doped in rigid Zeonex shows an 8.4-fold increase in emission intensity after evacuation. The optical sensor fabricated using the derivative of fluorinated triphenylpyrimidine and phenothiazine is characterized by the Stern-Volmer constant 1.37 × 10-4 ppm−1.

Photocycloaddition of Zero-Dimensional Metal Halide Hybrids with Reversible Photochromism.

In this work, two zero-dimensional (0D) metal halide hybrids L2ZnBr4 [1, L = (E)-4-(2-(1H-pyrrol-3-yl)vinyl)-1-methylpyridin-1-ium] and L6Pb3Br12 (2) were prepared, which demonstrated photochromism and photoinduced cracking. Upon irradiation at 450 nm, a single crystal-to-single crystal transformation occurred as a result of the [2 + 2] photocycloaddition of L. Interestingly, compared to the complete photocycloaddition of L in 1, only two-thirds of L monomers could be photodimerized in 2 because of the difference in L orientation. 1 shows reversible photochromic behavior including rapid response time, few cracks, high conversion rate, and good reaction reversibility, while 2 exhibits no significant color change but distinct photoinduced cracking because of the large local lattice strain induced by inhomogeneous and anisotropic deformation. Moreover, the photocycloaddition of L results in the distinct shift of photoluminescence of 1 and 2, attributed to the variation in conjugation of π electrons and distortion of metal halide clusters. As a proof-of-concept, reversible optical writing is demonstrated for 1. These findings provide new insights into the design of stimuli-responsive multifunctional materials.

Pentacenequinone-Modulated 2D GdSn-PQ Nanosheets as a Fluorescent Probe for the Detection of Enrofloxacin in Biological and Environmental Samples.

The fate and effects of fluoroquinolone antibacterial (FQ) on the environment are important since there appears to be a surge in FQ resistance like enrofloxacin (ENR) in both environmental and clinical organisms. Numerous reports indicate that the sensing capabilities of these antibiotics need to be improved. Here, we have investigated the interaction of ENR with our synthesized pentacenequinone-modulated gadolinium-tin (GdSn-PQ) nanosheets and the formation of intermolecular interactions that caused the occurrence of aggregation-induced emission enhancement. The concept for designing hybrid metallic nanosheets comes from the unique features inherited from the parent organic precursor. Due to the distinct interaction between ENR and GdSn-PQ, the interstate conversion (ISC) between GdSn-PQ and ENR induces a significant wavelength shift in photoluminescence (PL), improving reliability, selectivity, and visibility compared to quenching- or AIEE-based methods without peak shifts, allowing for highly sensitive and visually detectable analyses. The fluorescence signal of GdSn-PQ exhibited a linear relationship (R2 = 0.9911), with the added ENR concentrations ranging from 5 to 90 nM, with a detection limit of 0.10 nM. We have demonstrated its potential and wide use in the detection of ENR in biological samples (human urine and blood serum) and environmental samples (tap water and seawater) with a recovery rate of 98- 108%. The current approach has demonstrated that the 2D GdSn-PQ nanosheet is a novel and powerful platform for future biological and environmental studies.

Circularly Polarized Photoluminescence in Chiral Hybrid Organic–Inorganic Manganese Halide Perovskites: From Bulk Materials to Exfoliated Flakes

AbstractLayered hybrid organic–inorganic metal‐halide perovskites (HOIPs) can acquire chirality from molecules incorporated into their structure showing exciting possibilities in optoelectronics and spintronics. However, researchers have focused their attention on the study of bulk compounds, namely unstable and toxic Pb HOIPs. Herein, the chiroptical properties of R‐ and S‐β‐methylphenethylammonium Mn chloride HOIPs are reported in both the bulk and the few‐layer limit as exfoliated flakes. Red photoluminescence (PL) emission originating from the octahedrally coordinated Mn2+ is observed, with a PL shift to longer wavelengths when passing from bulk to flakes. Circular dichroism and circularly polarized PL mirrored‐signals for enantiomers are found in bulk samples, while in flakes, a degree of circularly polarized emission (P) of up to 17% at 80 K is achieved, comparable to Pb‐based HOIPs. Moreover, angle‐resolved PL measurements on flakes show that the PL emission and P are isotropic. These findings highlight the potential of these HOIPs from bulk to flakes for spin‐optoelectronic applications.

Iodo-bridged dicopper(I) complex containing a benzothienobenzothiophene unit: structure, characterization, and crystal-packing effects on solid-state photoluminescence

Abstract The title complex was newly synthesized by straightforward ligand substitution of a parent complex having a N2P2 set. The present complex had a deformed rhomboidal {Cu2I2} core with shortened Cu···Cu and prolonged I···I diagonals compared with those of the parent complex and formed one-dimensional channels filled with solvent molecules in crystals. The complex exhibited unusual red shift in solid-state photoluminescence assigned to halogen/metal-to-ligand charge transfer, indicating association of the unique crystal packing containing intramolecular electronic coupling between benzothienobenzothiophene moieties.

Red Photoluminescence from Fe-Doped MgAl2O4 Crystals

The influence of variations in composition (x = MgO/Al2O3 = 0.3–1.0), Fe2O3 concentrations (0.05 mol%–2.0 mol%), and O2 concentrations (100 vol% and 0 vol%) in the atmosphere on the PL characteristics of Fe-doped MgAl2O4 crystals were investigated using single phase spinel crystals grown by FZ technique. The peak wavelength shift of photoluminescence at around 730 nm are observed depending on the Fe2O3 concentration and composition. Concentration quenching of red PL occurred at Fe2O3 concentration above 0.1 mol%. PL intensity was higher in samples grown in 100 vol% O2 compared to those grown in 100 vol% Ar. PL intensity from Fe-doped MgAl2O4 increased with increasing compositions x from 0.3 to 1.0. MgAl2O4 doped with 0.1 mol% Fe2O3, and a stoichiometric composition (x = 1.0) grown in 100 vol% O2, demonstrated strong red PL with ultraviolet-C (UVC) lights excitation.

Effect of Lattice Disorder on Exciton Dynamics in Copper-Doped InP/ZnSexS1-x Core/Shell Quantum Dots.

InP/ZnSexS1-x core/shell quantum dots (QDs) with varying Cu concentrations were synthesized by a one-pot hot-injection method. X-ray diffraction and high-resolution transmission electron microscopy results indicate that Cu doping did not alter the crystal structure or particle size of the QDs. The optical shifts in UV-visible absorption and photoluminescence (PL) suggest changes in the electronic structure and induction of lattice disorder due to Cu doping. Ultrafast transient absorption spectroscopy (TAS) reveled that a higher Cu-doping level leads to faster charge carrier recombination, likely due to increased nonradiative decay from defect states. Time-resolved PL (TRPL) studies show longer average lifetimes of charge carriers with increased Cu doping. These findings informed the development of a kinetic model to better understand how Cu-induced disorder affects charge carrier dynamics in the QDs, which is important for emerging applications of Cu-doped InP/ZnSexS1-x QDs in optoelectronics.

Programming sp3 Quantum Defects along Carbon Nanotubes with Halogenated DNA.

Atomic defect color centers in solid-state systems hold immense potential to advance various quantum technologies. However, the fabrication of high-quality, densely packed defects presents a significant challenge. Herein we introduce a DNA-programmable photochemical approach for creating organic color-center quantum defects on semiconducting single-walled carbon nanotubes (SWCNTs). Key to this precision defect chemistry is the strategic substitution of thymine with halogenated uracil in DNA strands that are orderly wrapped around the nanotube. Photochemical activation of the reactive uracil initiates the formation of sp3 defects along the nanotube as deep exciton traps, with a pronounced photoluminescence shift from the nanotube band gap emission (by 191 meV for (6,5)-SWCNTs). Furthermore, by altering the DNA spacers, we achieve systematic control over the defect placements along the nanotube. This method, bridging advanced molecular chemistry with quantum materials science, marks a crucial step in crafting quantum defects for critical applications in quantum information science, imaging, and sensing.

Increasing the Structural Rigidity and Quantum Yield of Highly Emissive Hybrid Antimony Chlorides Using a Diverse Set of Solvent Guests

Abstract0D organic–inorganic antimony halides have attracted increasing attention due to the non‐toxicity, high stability, and superior photoluminescence quantum yield (PLQY). Here, a series of hybrid antimony chlorides with the same organic cation ethyltriphenylphosphonium (Ph3EtP+), including non‐emissive (Ph3EtP)2Sb2Cl8 and nine (Ph3EtP)2SbCl5‐based emissive compounds, are synthesized and characterized. These emissive compounds are namely, the guest‐free (Ph3EtP)2SbCl5 and (Ph3EtP)2SbCl5·guest (guest = glycol, acetic acid, methanol, ethanol, n‐propanol, i‐propanol, acetone, and acetonitrile). The solvent used can alter the coordination mode of Sb because the solvation effect affects the reactivity of the anions ([SbCl4]− and Cl−), leading to the formation of either A2Sb2Cl8 or A2SbCl5. The solvents can be even incorporated into the crystal structure, where stronger interaction with [SbCl5]2− leads to higher temperature of the escape of the solvent. The guest molecules could increase the structural rigidity of [SbCl5]2− via hydrogen bonding and dipole–dipole interactions, which tends to reduce the room‐temperature photoluminescence (PL) Stokes shift and temperature‐dependent PL shift by decreasing the [SbCl5]2− deformability, along with enhanced PLQY from 81% in guest‐free to near‐unity in (Ph3EtP)2SbCl5·glycol. This work shows that targeted synthesis and diversified choices of solvents provide an efficient tool to generate steady variations in hybrid emissive materials for optoelectronics.

Time-resolved study of laser-induced phase separation in CsPb(IxBr1−x)3 perovskite under high pressure

Mixed-halide perovskites have attracted extensive interest with their broadly tunable bandgap and optoelectronic properties, which makes them ideal candidates for various solar cells and light-emitting diodes. However, the mixed-halide perovskites often encounter phase separation and degradation under light illumination, which prevents them from many optoelectronic applications. The study on the underlying mechanism and the controlling of the phase separation is crucial to improve the tailored properties for practical applications. Here, we report our systematical investigations of the time-resolved photoluminescence shift and crystal structure evolution on the nanocrystalline CsPb(IxBr1−x)3 perovskite under intense laser illumination and found the increasing contribution of bromine-rich phase over time. Furthermore, we subject the nanocrystalline CsPb(IxBr1−x)3 perovskite to a quasi-hydrostatic pressure environment and observed that the phase separation slows down quickly with increasing pressure and can be totally suppressed at a rather mild pressure below 0.2 GPa. These findings suggest the light-induced separation of the crystalline structure, and their optoelectronic properties can be largely suppressed, which provides a useful approach to overcome the problem caused by the intense light applications.

Thermally activated delayed fluorescence emitters showing wide-range near-infrared piezochromism and their use in deep-red OLEDs.

Organic small molecules exhibiting both thermally activated delayed fluorescence (TADF) and wide-ranging piezochromism (Δλ > 150 nm) in the near-infrared region have rarely been reported in the literature. We present three emitters MeTPA-BQ, tBuTPA-BQ and TPPA-BQ based on a hybrid acceptor, benzo[g]quinoxaline-5,10-dione, that emit via TADF, having photoluminescence quantum yields, ΦPL, of 39-42% at photoluminescence (PL) maxima, λPL, of 625-670 nm in 2 wt% doped films in 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP). Despite their similar chemical structures, the PL properties in the crystalline states of MeTPA-BQ (λem = 735 nm, ΦPL = 2%) and tBuTPA-BQ (λem = 657 nm, ΦPL = 11%) are significantly different. Further, compounds tBuTPA-BQ and TPPA-BQ showed a significant PL shift of ∼98 and ∼165 nm upon grinding of the crystalline samples, respectively. Deep-red organic light-emitting diodes with MeTPA-BQ and tBuTPA-BQ were also fabricated, which showed maximum external quantum efficiencies, EQEmax, of 10.1% (λEL = 650 nm) and 8.5% (λEL = 670 nm), respectively.

Regulation of aggregation-induced emission and reversible remarkable mechanofluorochromism by substitution position of the carbazole unit in D-A type carbazole-functionalized dicyanoethylene π-systems

In this study, two twisted D-A type dibenzothiophene- and carbazole-functionalized dicyanoethylene derivatives were formulated and synthesized. They were labeled as 2-substituted carbazole (BT-CE-C2) and 3-substituted carbazole (BT-CE-C3), respectively. Furthermore, an investigation into the correlation between the molecular structure of these derivates and their photophysical properties was conducted. The characteristic D-A structures and the highly distorted spatial conformations of the two fluorophores led to the emergence of a unique intramolecular charge transfer (ICT) effect and remarkable aggregation-induced emission (AIE) behavior. Notably, the position of substitution of the carbazole unit regulated the reversible high-contrast mechanofluorochromic (MFC) properties demonstrated by BT-CE-C2 and BT-CE-C3. The as-prepared solid powders of BT-CE-C2 and BT-CE-C3 produce blue-green and orange-yellow emissions at 508 and 567 nm, respectively. However, their ground powders emitted orange (at 589 nm) and orange-red (at 619 nm) lights. Notably, BT-CE-C2 exhibited enhanced fluorescence upon external stimulation, increasing its solid-state luminescence efficiency from 0.035 to 0.189. In contrast, the BT-CE-C3 exhibited a decrease in fluorescence, causing its solid-state luminescence efficiency to change from 0.426 to 0.348. The fluorescence lifetimes, powder X-ray diffraction (PXRD), and spectral analysis collectively identified the phase transition between the crystalline and amorphous states as the underlying cause of the MFC behavior observed in BT-CE-C2 and BT-CE-C3. Additionally, the red shift in photoluminescence (PL) spectra under external stimulus can be attributed to planarized-induced charge transfer (PICT), exciton coupling, increased π-π interactions, and enhanced orbital overlap between adjacent molecules. This combination of factors led to the observed MFC properties of these compounds.

(Invited) Formation and Characterization of Fe-Silicide Nanodots for Optoelectronic Application

We have demonstrated the formation of high areal-density β-FeSi2nanodots (NDs) on SiO2 by remote H2-plasma induced self-assembly of Fe-NDs and subsequent SiH4-exposure at 400°C. Under either 976- or 514.5-nm light excitation of NDs after the SiH4-exposure, stable photoluminescence (PL) signals, being characteristic of the semiconducting phase as β-FeSi2, were observed even at room temperature in the energy region over the indirect bandgap of bulk β-FeSi2 (~0.7 eV). The temperature dependence of PL was confirmed to be weak significantly in comparison to that of bulk bandgap, implying light emission from tightly confined NDs. And also, with a decrease in the average dot size by controlling the initial Fe-film thickness, a clear blue shift in PL was observed. The results are associated with quantum size effect in radiative recombination of photoexcited electron-hole pairs.

ZnO nanorods on conductive substrates. Technology and features

For obtaining ZnO nanorods (NRs) on the surface of highly conductive brass substrates, the technology of surface oxidation in argon plasma ion flows was developed that allows the formation of NRs by high-frequency helicon discharge at temperatures T ≤ 550 °C. A physical mechanism for the formation of ZnO NRs on the brass substrate is considered. The morphological, structural and physical properties of the NR samples were investigated using standard methods of research: scanning electron microscopy, energy dispersion analysis, X-ray diffraction analysis, Raman scattering, photoluminescence and optical reflectance spectra. The features of the ZnO NRs’ optical reflectance properties in terms of the location of the Restrahlen band are discussed. The quality of such nanorods is confirmed by fine details in photoluminescence and Raman shift data.

Thermostimulated luminescence analysis of oxygen vacancies in HfO[formula omitted] nanoparticles

Hafnia has already been established in CMOS technologies as a high-k metal gate material, however, recently it has also become a promising material in ferroelectric applications. In this study we have investigated intrinsic defects such as oxygen vacancies in undoped and 5at%Eu HfO2 synthesized by sol-gel, combustion, auto-ignition combustion, hydrothermal and precipitation methods. All samples were of monoclinic phase with crystallite sizes of 16–40 nm. Photoluminescence (PL), thermostimulated luminescence (TSL) both below and above room temperature as well as XRD and TEM methods were used to identify potential VO3+1, VO3+2, VO4+1 and VO4+2 defects. Activation energies were determined for the oxygen vacancies and grain boundary effects were studied. Both PL and TSL wavelength peak spectra shift to higher energies with the increase of temperature was observed.

Synthesis and Application of Carbon Quantum Dots Derived from Carbon Black in Bioimaging.

Carbon quantum dots (CQDs) are a new type of fluorescent QDs that consists mainly of carbon atoms. In this research, CQDs were synthesized through harsh oxidizing conditions applied on carbon black and subsequent N-doping using hexamethylenetetramine (Hexamine) and polyethyleneimine (PEI). The synthesized CQDs were characterized using FTIR, AFM, UV-Visible spectroscopy, photoluminescence (PL) spectroscopy, and fluorescence imaging respectively. The AFM images showed that the dots are in the range of 2-8nm. N-doping of the CQDs increased the PL intensity. The PL enhancement for the CQDs that were N-doped with PEI was higher compared to those N-doped with hexamine. The shift in PL by changing the excitation wavelength has been attributed to the nano-size of the CQDs, functional groups, defect traps, and quantum confinement effect. The in vitro fluorescence imaging revealed that N-doped CQDs can internalize into the cells and be used for fluorescent cell imaging.