Aggregation-induced Enhanced Emission Properties Research Articles

Aggregation-induced enhanced fluorescence emission of chiral Zn(II) complexes coordinated by Schiff-base type binaphthyl ligands.

A pair of novel chiral Zn(II) complexes coordinated by Schiff-base type ligands derived from BINOL (1,1'-bi-2-naphthol), R-/S-Zn, were synthesized. X-ray crystallography revealed the presence of two crystallographically independent complexes; one has a distorted trigonal-bipyramidal structure coordinated by two binaphthyl ligands and one disordered methanol molecule (molecule A), while the other has a distorted tetrahedral structure coordinated by two binaphthyl ligands (molecule B). Numerous CH⋯π and CH⋯O interactions were identified, contributing to the formation of a 3-dimensional rigid network structure. Both R-/S-Zn exhibited fluorescence in both CH2Cl2 solutions and powder samples, with the photoluminescence quantum yields (PLQYs) of powder samples being twice as large as those in solutions, indicating aggregation-induced enhanced emission (AIEE). The AIEE properties were attributed to the restraint of the molecular motion arising from the 3-dimensional intermolecular interactions. CD and CPL spectra were observed for R-/S-Zn in both solutions and powders. The dissymmetry factors, gabs and gCPL values, were within the order of 10-3 to 10-4 magnitudes, comparable to those reported for chiral Zn(II) complexes in previous studies.

Color tunable benzothiadiazole-based small molecules for lightening applications

Abstract 2,1,3-Benzothiadiazole (BTD) is a key motif for the chemistry of photoluminescence molecules and its application in lightening technology as well as cell imagining. Evaluating the characteristics and reaction mechanisms of the BTD derivatives in molecular is critical for molecular designing. Research has been turned to BTD-extended derivatives owing to their possible usage in organic photovoltaics, organic light-emitting diodes, liquid crystal devices, dye-sensitized solar cells, and many other applications. Herein, three small molecules with a BTD core, 4,7-di-m-tolylbenzo[c][1,2,5]thiadiazole (NK1), 4,7-bis(3,4,5-trifluorophenyl)benzo[c][1,2,5]thiadiazole (NK2), and 4,7-bis(5-(m-tolyl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (NK3), were designed and synthesized and their molecular structures were elucidated. Additionally, their photophysical and electrochemical behaviors as well as the aggregation-induced enhanced emission properties were examined to investigate their possible usage in cell imaging and organic electronic applications. The HOMO energy level of molecules has been found as −5.96, −5.58, and −5.60 eV, respectively. In the emission spectra, it was seen that molecules showed green, blue, and red emission, respectively.

Paper-based device for nanomolar detection of Cd2+ using AIEE-active imidazolium ionic liquid functionalized phenothiazine based Schiff-Base

A highly green fluorescent phenothiazine-based imidazolium ionic liquid (IL) [PTZ-SB][Br] was synthesized and its structure was thoroughly elucidated by 1H, 13C NMR, FT-IR, UV–visible spectroscopy and Mass spectrometry. Furthermore, thermal resilience of the IL was established by TGA and DSC investigations. The novel molecule revealed a distinct recognition for Cd2+ ions over eleven other transition metal ions. Moreover, the promising results obtained in the solution phase interested us to embed [PTZ-SB][Br] on paper strips to create a paper-based fluorescent sensor, which was examined by a portable UV light source for the on-site Cd2+ detection. Interestingly, the device demonstrated exceptional fluorescence sensing behavior towards Cd2+ with a limit of detection (LOD) of 0.16 nM. Thus, the probe has noteworthy distinct and sensitive detection ability towards Cd2+, which might find practical and on-spot applications. Noticeably, [PTZ-SB][Br] demonstrated aggregation-induced enhanced emission (AIEE) phenomenon. In fact, an incredible 38.1-fold increase in fluorescence intensity was observed for 10:90 ratio of THF:water mixture as compared that for pure THF solution of [PTZ-SB][Br]. AIEE property was further supported by DLS studies. A paper-based device for Cd2+ sensing by applying an Ionic Liquid based Schiff base is reported herein for the first time.

A novel pyrene-based aggregation induced enhanced emission active Schiff base fluorophore as a selective “turn-on” sensor for Sn2+ ions and its application in lung adenocarcinoma cells

Schiff bases are an important class of compounds that are highly instrumental in complex formation as well as act as sensors for various metal ions. Herein, 1-aminopyrene was reacted with 5-bromo-2-thiophene carboxaldehyde to synthesize a designed Schiff base, PY-SB (N-((5-bromothiophen-2-yl) methylene) pyrene-2-amine) as a condensation product. The authenticity of the synthesized Schiff base compound was established using 1H NMR, 13C NMR, IR and HRMS techniques. Among the optoelectronic investigations, the AIEE (Aggregation Induced enhanced emission) property of PY-SB was explored and it showed 24 folds enhancement in fluorescence intensity in tetrahydrofuran (THF) and water mixtures (50:50). AIEE results were further supported by DLS (Dynamic Light scattering) study. In addition, PY-SB was found to be a highly selective and sensitive tool for the “turn-on” detection of Sn2+ ion. The turn–on fluorescence of PY-SB is due to the PET-OFF process. The electron transfer from nitrogen to the pyrene ring is completely blocked due to the formation of a complex of PY-SB with insitu generated Sn2 species(PY-SB + Sn2), which causes PET-OFF. The detection limit and binding constant of PY-SB towards Sn2+ ion were found to be 5.4 µM, and 2 × 104 M−1, respectively. The stoichiometric study through Job’s plot reveals the development of 2:1 ratio (Sn2: PY-SB) of complexation which is further confirmed by DFT, ES-MS, 1H NMR and 13C NMR, SEM-EDX. To verify the sensing behavior of PY-SB in a biological system, in vitro studies on lung adenocarcinoma cells were successfully carried out and they showed similar behavior as seen in the cuvette study.

Protonation induced redshift in the fluorescence of a pyridine derivative as a potential anti-counterfeiting agent.

A simple pyridine-based compound, i.e. (2,4,6-tris(4-(hexyloxy)phenyl)pyridine), was synthesized and exhibited excellent solubility in various organic solvents owing to the presence of three 4-n-hexyloxy chains in its molecular structure. Further, we studied the effect of various solvents on its absorption and emission properties. We observed a greater extent of redshift in the chloroform solvent compared to the rest of the solvents. In fact, the observed redshift was attributed to protonation of the pyridine moiety by HCl (present due to the oxidative photo-decomposition of chloroform) in the solvent. Therefore, we also studied the acidochromic properties of the compound using acetic acid (AA), trifluoroacetic acid (TFA), and hydrochloric acid (HCl). We found that the compound sensed the HCl vapor much more efficiently than the TFA and AA vapours. Additionally, DFT analysis suggested a narrow theoretical bandgap for the protonated molecule when compared to the neutral molecule, explaining the redshift in the absorption and emission spectra of the protonated molecule. Furthermore, the compound exhibited a good level of aggregation induced enhanced emission (AIEE) in the THF-water system. In fact, compounds showing both AIEE and acidochromism are rarely reported in the literature. Finally, we employed it as an anti-counterfeiting agent based on its acid-base vapour sensing capability.

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.

Aggregation-induced enhanced emission of a carbazole derivative with asymmetric group

A novel carbazole-based compound (L) has been synthesized with an asymmetric group, which possesses obviously intramolecular charge transfer (ICT) process that was confirmed from the positive solvatochromic photophysical properties in different polar solvents. The introduction of nitro unit into L structure led the weak fluorescence emission, caused from the strong electron accepting character of nitro unit. L also demonstrated to exhibit superior aggregation-induced enhanced emission (AIEE) properties. The torsion degree between C1-C18 bond and N19-C23 bond was 94.098°, the introduction of benzoimidazolylcarbazole attached to the carbazole core generated the torsion degree of the whole molecule, which prevented π-π stacking between adjacent molecules and brought about AIEE property. The results were verified by time dependent density functional theory (TD-DFT) calculations. The tortuosity of L molecule also brought about inferior planarity in whole molecule, then the molecules of L can organize through intermolecular interactions to form tiny crystals at nanosacle in water-medium solutions. The AIEE character of L was effectively applied in bioimaging of HepG2 cancer cells.

Tailoring the sensing behaviors to Zn2+ and AIEE properties of phenanthroline derivatives through isomer engineering

Three isomeric phenanthroline compounds, namely 2-DP, 3-DP and 5-DP, are constructed by incorporating 4-(2,2-diphenyl-vinyl)-phenyl unit into 2-, 3-, and 5-positions of phenanthroline. This approach functionalizes these compounds to exhibit different solvatochromism effects and metal-ion sensing abilities. 2-DP shows no obvious sensitivity for proton solvent and metal ions, but it's quite the opposite for 3-DP and 5-DP. Significantly, 3-DP possesses higher selectivity and sensitivity to Zn2+ than 5-DP to Zn2+, with a limit of detection down to 10−8 M. The density function theory calculations reveal that their different sensing behaviors are related to their steric hindrance and electronic effects. Moreover, 2-DP, 3-DP and 5-DP all exhibit aggregation-induced enhanced emission (AIEE), in which the photoluminescence (PL) enhancement of 2-DP is the biggest in aggregated state. It is thought that the molecule torsion degree is responsible for their different AIEE behaviors, which is supported by the X-ray structural analysis. The isomer engineering for phenanthroline provides a simple method to enhance the selectivity and sensitivity to metal ions, and to optimize solid-state luminescence properties.

High fluorescence of carbazole derivatives for bioimaging of endoplasmic reticulum and lysosome: the influence of molecular structure on optical properties and cell uptake

Three new carbazole derivatives (L1–L3) with different functional groups have been synthesized and characterized. L1 and L2 are connected through methylene unit to construct L3 with enhanced molecular distortion configuration. The compounds exhibit dependent aggregation-induced enhanced emission (AIEE) properties and cellar uptake region in HepG2 cells. It is demonstrated that L1 and L2 exhibit modest AIEE properties in THF–H2O mixtures, while L3 shows superior AIEE character with 13 times enhancement. This is because of the enhanced molecular distortion configuration of L3 and the related restriction of π–π stacking interactions between adjacent L3 molecules resulted from the introduction of methylene unit. Due to the unique structure of the compounds, the superior fluorescence emission of L1–L3 in aqueous media, further imaging studies demonstrated the suitability of probes L1–L3 for the biological applications in both human liver hepatocellular carcinoma cells (HepG2) and plant tissues of Arabidopsis seedlings. The imidazole unit in L2 leads selective target to lysosome of HepG2 cells through acid–base interactions, while L1 and L3 are inclined to act with endoplasmic reticulum.

Pyrene based chalcone materials as solid state luminogens with aggregation-induced enhanced emission properties

Abstract New series of pyrene based chalcone materials were synthesized by Claisen-Schmidt condensation exhibits dual characteristics such as aggregation-induced enhanced emission (AIEE) in solution as well as solid state luminescence. The photo-physical properties such as solvent effect, quantum yield and lifetime of materials were studied. They were demonstrated aggregation induced enhanced emission (AIEE) with broad colour changes from green to orange emission on different water fraction in THF/H 2 O mixture. The bulky group of pyrene attached to vinylene keto heterocyclic moiety disturbs the polarity of pyrene prevents π-π stacking and restriction of intramolecular rotation (RIR) in aggregated state is the possible cause for its emission enhancement. The significant unusual blue shift in aggregated state observed when water volume exceeds more than 80% in THF dependent on morphological changes from amorphous to crystalline state. The energy level of materials was derived from experimental as well as theoretical calculation. One of fascinating characteristics of chalcone is its low cost, trouble-free synthetic procedure, nontoxic and tuning emission properties. The obtained results are promising as organic luminescent as well as semiconducting materials.

A novel D-A-D-A-D type molecule based on substituted dihydroindolo [3, 2-b] carbazole with large two-photon absorption cross section and excellent aggregation-induced enhanced emission property

Two novel D-A-D-A-D type molecules T1 and T2 based on substituted dihydroindolo [3, 2-b] carbazole with large two-photon absorption (2PA) cross section and excellent aggregation-induced enhanced emission (AIEE) property have been synthesized and characterized. Both compounds emit weakly fluorescent in THF, while a significant AIEE property is observed in water/THF (v/v 50%/50%) for T1 and water/THF (v/v 90%/10%) for T2 with a sharp increase in fluorescence intensity. The solid fluorescence of T1 and T2 is located at 575 nm and 588 nm, and their quantum efficiencies are determined to be 3.2% and 5.8%, respectively. The corresponding 2PA cross section values for T1 and T2 at 800 nm are 867 GM and 1300 GM by the open-aperture Z-scan technique. These excellent performances of both compounds make them as attractive alternatives for biophotonic and optoelectronic applications.

White Light Emitting Polymers from a Luminogen with Local Polarity Induced Enhanced Emission

Aggregation induced enhanced emission (AIEE) is considered as an important tool to circumvent the aggregation caused quenching (ACQ) effect in organic light emitting diodes (OLEDs). Charge trapping and surplus long wavelength electroluminescence is a cause of concern in single polymer based white OLEDs. However, the potential of luminogens with AIEE property as a credible tool to offset the above problems in white light emitting single polymer is not properly explored. In this study design, synthesis and spectral characterization of a polymerizable luminogen, (2Z,2′Z)-6,6′-(2,7-dibromo-9H-fluorene-9,9-diyl)bis(hexane-6,1-diyl)bis(2-cyano-3-(10-hexyl-10H-phenothiazin-3-yl)acrylate(FCPA) with AIEE property and its copolymers is presented. Lippert-Mataga studies showed that reduced local polarity caused by aliphatic chains in condensed state of FCPA resulted in AIEE property. The copolymers P(FCPA-1) and P(FCPA-0.5) with 1% and 0.5% FCPA moieties showed white electroluminescence and enhanced thin film photol...

Synthesis of two novel indolo[3,2-b]carbazole derivatives with aggregation-enhanced emission property

Luminogenic materials with AIE (aggregation-induced emission) and AIEE (aggregation-induced enhanced emission) characteristics have attracted substantial research interest due to their potential applications in optics, electronics environmental and the biological sciences. Here, we successfully synthesized two novel indolo[3,2-b]carbazole derivatives (compounds 3 and 4) with strong symmetrical groups, which were demonstrated to exhibit superior AIEE properties. Both 3 and 4 contain the same π-conjugated core structure, but slightly differ in the cyano-substituted stilbene group, giving rise to a high charge mobility, similar optical properties and energy band-gaps. The bulky cyano group attached to a vinylene moiety generates intramolecular co-planarity and prevents π–π stacking, whereby the emission in the aggregates can be enhanced. In addition, it is found that the cyano group also plays an important role in the formation of J-type aggregation, which is advantageous to the appearance of AIE and/or AIEE properties. A slight modification of the terminal substituent group renders compounds 3 and 4 AIEE properties entirely. As revealed by crystallographic data, the multiple intermolecular hydrogen bonding in 4 restricts intramolecular vibration and rotation, which enables 4 to emit intensely in the solid state. Moreover, cyano groups endow 3 with an improved self-assembly ability under the proper conditions. The molecules of 3 self-organize into one-dimensional ordered microfibers and/or nanorods that show a significant optical waveguide with different water fractions, indicating that the aqueous suspension of microfibers favors fluorescence emission. Our results demonstrate that the AIEE properties of the novel indolo[3,2-b]carbazole derivatives are highly related to the molecular structure and aggregate packing.

Aggregation-induced enhanced emission materials for efficient white organic light-emitting devices

We demonstrated the first aggregation-induced enhanced emission (AIEE) materials for white organic light-emitting diodes (WOLEDs). AIEE properties of materials provide a possibility to turnaround the bad thermal effects to positive effects for device performance as WOLEDs working under the condition of the high brightness and high current density. The blue AIEE molecule TDPVBi shows high glass transition temperature ( T g ) and special applicability for OLEDs, ca. enhanced smoothness as annealing its film. Constructing WOLED by combining both AIEE materials ( TDPVBi and CN-DPASDB) results in devices with a maximum current efficiency of 7.9 cd A −1, a maximum power efficiency of 6.2 lm W −1 and a maximum luminance of 25350 cd m −2, respectively. The AIEE WOLED displays simplification in device fabrication and excellent color stability, which belongs to the best fluorescent WOLED reported.