Photochromism and single-component white light emission from a metalloviologen complex based on 1,5-naphthyridine

Metalloviologens, as emerging electron-transfer photochromic compounds, have shown intriguing properties such as radiochromism, photochromism and photoconductance. However, only a limited number of them have been reported so far. Exploration of new metalloviologens is strongly desired. Herein, we report a new solvothermally synthesized metalloviologen complex [CdCl2(ND)2]n (1, ND = 1,5-naphthalenes) that exhibits photochromic and intrinsic white light emission properties. Density functional theory calculation results reveal that the photochromism could be assigned to photoinduced electron transfer from chlorine atoms to ND molecules. The photoinduced charge-separated states are heat/air stable, attributed to the delocalization of ND and strong intermolecular π-π interactions. Besides, complex 1 consistently emits intrinsic white light when excited with 340-370 nm UV light, achieving high color rendering index (CRI) values (82.54-94.04). By adjusting the excitation wavelength, both "warm" and "cold" white light emission can be produced, making it suitable for the application of a white light emitting diode (WLED). Thus, this work demonstrates that the ND-based metalloviologen is not only helpful in producing photochromism, but also beneficial for creating white-light emission.

Realization of white-light-emitting diodes from a high-brightness zirconium-based metal-organic gel driven by the AIE effect

Developing luminescent materials with suitable correlated color temperature (CCT) and sufficient color-rendering index (CRI) is a challenging problem in the field of commercialized warm white LED lighting. Herein, a novel metal-organic gel (MOG) material named YTU-G-1(SE) was synthesized, consisting of zirconium metal coordinated with 1,1,2,2-tetrakis(4-carboxyphenyl) ethylene. YTU-G-1(SE) exhibits strong fluorescent properties with an aggregation-induced emission (AIE) effect, emitting yellow-green fluorescence at 515 nm. The internal and external quantum efficiencies (IQE/EQE) of YTU-G-1(SE) are close to unity, with values of 95.74 ± 0.5% and 88.67 ± 0.5%, respectively. Finally, we combined YTU-G-1(SE) with a commercial blue chip and a commercial red phosphor (Sr,Ca)AlSiN3:Eu2+ to fabricate a warm white light LED with a color temperature of 3736 K, a color-rendering index Ra of 88.2, and a lumen efficiency of 79.42 lm W-1. This work provides a new approach to regulating the emission of AIE and offers a novel idea for developing high-performance warm-white pc-WLEDs.

Tuning the Emission of Homometallic DyIII, TbIII, and EuIII 1-D Coordination Polymers with 2,6-Di(1H-1,2,4-triazole-1-yl-methyl)-4-R-phenoxo Ligands: Sensitization through the Singlet State

This work reports the structural characterization and photophysical properties of DyIII, TbIII, and EuIII coordination polymers with two phenoxo-triazole-based ligands [2,6-di(1H-1,2,4-triazole-1-yl-methyl)-4-R-phenoxo, LRTr (R = CH3; Cl)]. These ligands permitted us to obtain isostructural polymers, described as a 1D double chain, with LnIII being nona-coordinated. The energies of the ligand triplet (T1) states were estimated using low-temperature time-resolved emission spectra of YIII analogues. Compounds with LClTr present higher emission intensity than those with LMeTr. The emission of TbIII compounds was not affected by the different excitation wavelengths used and was emitted in the pure green region. In contrast, DyLMeTr emits in the blue-to-white region, while the luminescence of DyLClTr remains in the white region for all excitation wavelengths. On the other hand, EuIII compounds emit in the blue (ligand) or red region (EuIII) depending on the substituent of the phenoxo moiety and excitation wavelength. Theoretical calculations were employed to determine the excited states of the ligands by using time-dependent density functional theory. These calculations aided in modeling the intramolecular energy transfer and rationalizing the optical properties and demonstrated that the sensitization of the LnIII ions is driven via S1 → LnIII, a process that is less common as compared to T1 → LnIII.

Efficient manipulation of Förster resonance energy transfer through host-guest interaction enables tunable white-light emission and devices in heterotopic bisnanohoops

In this study, we synthesized and reported the heterotopic bisnanohoops P5-[8,10]CPPs containing cycloparaphenylenes (CPPs) and a pillar[5]arene unit, which act not only as energy donors but also as a host for binding energy acceptors. We demonstrated that a series of elegant FRET systems could be constructed successfully through self-assembly between donors P5-[8,10]CPPs and acceptors with different emissions via host-guest interaction. These FRET systems further allow us to finely adjust the donors P5-[8,10]CPPs and acceptors (BODIPY-Br and Rh-Br) for achieving multiple color-tunable emissions, particularly white-light emission. More importantly, these host-guest complexes were successfully utilized in the fabrication of white-light fluorescent films and further integrated with a 365 nm LED lamp to create white LED devices. The findings highlight a new application of carbon nanorings in white-light emission materials, beyond the common recognition of π-conjugated molecules.

Single-Component White Light Emission from a Metal-Coordinated Cyclotriveratrylene-Based Coordination Polymer

A coordination polymer, namely, [Cd₃L(H₂O)₃]·DMA·4H₂O (1) (DMA = N,N-dimethylacetamide), was prepared by the solvothermal reaction of cyclotriveratrylene-based ligand 5,6,12,13,19,20-hexacarboxy-methoxy-cyclotriveratrylene (H₆L) and Cd(NO₃)₂·4H₂O. In 1, a two-dimensional structure was constructed by the connection of hexanuclear Cd-O clusters and L^6- anions. Photoluminescence measurements indicated that 1 displayed tunable photoluminescence through the variation of the excitation wavelength. Significantly, the white light emission of 1 can be observed with a broad excitation wavelength range from 320 to 385 nm. When 1 is excited by 385 nm light, its chromatic coordinate is (0.29, 0.34), which is located very close to the pure white light region (0.33, 0.33). Meanwhile, the color temperature (CCT) is 7994 K, which corresponds well to "cold" white light.

Pillararene-Induced Intramolecular Through-Space Charge Transfer and Single-Molecule White-Light Emission

The fabrication of single-molecule white-light emission (SMWLE) materials has become a highly studied topic in recent years and through-space charge transfer (TSCT) is emerging as an important concept in this field. However, the preparation of ideal TSCT-based SMWLE materials is still a big challenge. Herein, we report a bifunctional pillar[5]arene (TPCN-P5-TPA) with a linear donor-spacer-acceptor structure and aggregation-induced emission (AIE) property. The bulky pillar[5]arene between the donor and acceptor induces a twisted conformation and a non-conjugated structure, resulting in intramolecular TSCT. In addition, the AIE feature and pillar[5]arene cavity endow TPCN-P5-TPA with responsiveness to viscosity and polar guests, by which the TSCT emission is triggered. The combination of blue locally-excited state emission and yellow TSCT emission of TPCN-P5-TPA generates SMWLE. Therefore, we provide a new and versatile strategy for the construction of TSCT-based SMWLE materials.

Self-Propelled Motion Sensitive to the Chemical Structure of Amphiphilic Molecular Layer on an Aqueous Phase

Two novel amphiphiles, N-(3-nitrophenyl)stearamide (MANA) and N,N′-(4-nitro-1,3-phenylene)distearamide (OPANA), were synthesized by reacting nitroanilines with one or two equivalents of stearic acid. We investigated how the molecular structures of these compounds influenced the characteristics of a self-propelled camphor disk placed on a monolayer of the synthesized amphiphiles. Three types of motion were observed at different surface pressures (Π): continuous motion (Π < 4 mN m⁻¹), deceleration (4 mN ≤ Π ≤ 20 mN m⁻¹), and no motion (Π > 20 mN m⁻¹). The speed of the motion of the camphor disks was inversely related to Π for both MANA and OPANA at the temperatures tested, when Π increased in the respective molecular layers under compression. The spectroscopic evidence from UV-Vis, NMR, and ESI-TOF-MS revealed that the dependence of the speed of the motion on Π originates from the intermolecular interactions that are present in the monolayers. This study suggests that it is possible to control the self-propelled motion by manipulating contributing factors at the molecular level.

Single-Molecule White-Light-Emitting Starburst Donor-Acceptor Triphenylamine Derivatives and Their Application as Ratiometric Luminescent Molecular Thermometers

White-light emission (WLE) from a single molecule is a highly desirable alternative to a complex mixture of complementary colour emitters, which suffers from poor stability and reproducibility for potential use in organic electronic devices and lighting applications. We report single-molecule WLE both in solution and thin films by judiciously controlled π-electron delocalisation between the triarylamine subchromophoric units. Triphenylamine (TPA) forms the central core, and the phenyl rings are substituted with the electron-deficient acceptor 3-ethylrhodanine (Rh) and electron-rich donors triphenylamine or carbazole. The enforced biphenyl configuration of the TPA core and the other donors renders the π-conjugation across the entire chromophore poor, thus the individual subchromophoric units retain their individual emission characteristics, which cover all three primary colour emissions, that is, red, green and blue (RGB). TPA-Rh units exhibit broad fluorescence in the green-red region originating from the local excited (LE) state and intramolecular charge transfer state (ICT), strongly influenced by the solvent, water, and temperature. Different fluorescence parameters, including spectral maxima, ratiometric changes in ICT emission at the expense of blue emission from terminal donor units, and changes in lifetime, have a linear relationship with temperature between 180-330 K, thus the molecules can function as a multiparameter luminescent molecular thermometer. A temperature coefficient of 0.19 K^-1 in ratiometric fluorescence changes along with a spectral shift of 0.3 nm K^-1 and their workability over the wide temperature makes these molecules promising materials for potential applications. At lower temperatures, individual subchromophoric properties subside because of the reduced dihedral angle of biphenyl, and fluorescence from the whole molecule becomes dominant.

Combining Dual-Light Emissions to Achieve Efficient Broadband Yellowish-Green Luminescence in One-Dimensional Hybrid Lead Halides

In recent years, low-dimensional lead halides have emerged as some of most attractive photoelectric materials due to their intrinsic broadband emissions with a potential application in white-light emitting diodes. To achieve the desired performance, tremendous research has emphasized the modulation of inorganic components as optical centers; however, less work has paid attention to the direct contribution of the organic components. Herein, we successfully assembled two new hybrid lead halides of [H₂BPP]Pb₂X₆ (X = Br, 1, and Cl, 2) containing one-dimensional double [Pb₂X₆]^2- chains using optically active 1,3-bis(4-pyridyl)-propane (BPP) as an organic cation. Under UV-light excitation, compounds 1 and 2 exhibit broadband yellowish-green emissions, which were verified by promising photoluminescence quantum efficiencies (PLQEs) of 8.10% and 4.84%, respectively. The broadband light emissions are derived from the combination of dual higher-energy blue and lower-energy yellow light spectra, which can be attributed to the individual contributions of the organic and inorganic components, respectively, according to the time-resolved and temperature-dependent emission spectra as well as theoretical calculations. This work proves the great contribution of organic components to the photophysical properties and provides a new design strategy to realize broadband light emission by rationally combining the dual-emitting properties of different assembly blocks.

Expanded benzofuran-decorated twistacene derivatives: synthesis, characterization and single-component white electroluminescence

Two novel phenanthro[9,10-b]benzofuran and pyreno[4,5-b]benzofuran modified twistacene derivatives, 9 and 10, have been successfully synthesized via Suzuki coupling and then characterized. The photophysical properties were examined and DFT calculations were carried out in a comparative manner, and both molecules emitted strong blue light in organic solvents and in the solid state. Impressively, fabricated electroluminescent devices based on these single emitters radiate pure white light.

Single-Molecular White-Light Emitters and Their Potential WOLED Applications

White organic light-emitting diodes (WOLEDs) are superior to traditional incandescent light bulbs and compact fluorescent lamps in terms of their merits in ensuring pure white-light emission, low-energy consumption, large-area thin-film fabrication, etc. Unfortunately, WOLEDs based on multilayered or multicomponent (red, green, and blue (RGB)) emissive layers can suffer from some remarkable disadvantages, such as intricate device fabrication and voltage-dependent emission color, etc. Single molecules, which can emit white light, can be used to replace multiple emitters, leading to a simplified fabrication process, stable and reproducible WOLEDs. Recently, the performance of WOLEDs by using single molecules is catching up with that of the state-of-the-art devices fabricated by multicomponent emitters. Therefore, an increasing attention has been paid on single white-light-emitting materials for efficient WOLEDs. In this review, different mechanisms of white-light emission from a single molecule and the performance of single-molecule-based WOLEDs are collected and expounded, hoping to light up the interesting subject on single-molecule white-light-emitting materials, which have great potential as white-light emitters for illumination and lighting applications in the world.

Heat-resistant Pb(ii)-based X-ray scintillating metal–organic frameworks for sensitive dosage detection via an aggregation-induced luminescent chromophore

Unusual X-aggregation induced luminescent chromophores in heat-resistant Pb(ii)-based metal–organic frameworks facilitate excellent scintillation for X-ray dosage detection.

Excitation Wavelength-Dependent Nearly Pure White Light-Emitting Crystals from a Single Gold(I)-Containing Complex

A gold(I) complex is reported. Interestingly, crystals of the gold(I) complex exhibit an excellent excitation wavelength-dependent emission effect at room temperature. Notably, a nearly pure white emission with Commission Internationale de L'Eclairage (CIE) 1931 chromaticity coordinates of (0.32, 0.33) is obtained upon excitation with 406 nm light.

Energy transfer-mediated white light emission from Nile red-doped 9,10-diphenylanthracene nanoaggregates upon excitation with near UV light

The low cost, ease of preparation, colour tunability and wide application range garnered huge research interest on organic light emitting diode materials (OLED). The development of white light-emitting organic diode materials is mostly targeted for this. Anthracene derivatives have recently emerged as low-cost and efficient blue light-emitting diodes. However, developing efficient organic diode materials that cover the entire visible spectrum is very challenging. Herein, we demonstrated that Nile red (NR)-doped 9,10-diphenylanthracene (DPA) nanoaggregates provided strong white light emission upon excitation with near UV light. The dual emissions of the DPA nanoaggregates covering the blue and green regions were exploited and combined with the controlled red emission of the properly doped NR dye to cover the full visible spectrum, rendering white light emission with a quantum yield of >0.4. The fluorescence spectra of the DPA nanoaggregates doped with NR at various concentrations were monitored and their CIE coordinates were followed to evaluate the proper doping ratio for equal-energy white-light emission. Concurrent time-resolved emission studies provided mechanistic insights into the energy transfer from the exciton and excimer states of DPA to NR. It was revealed that the energy transfer from the singlet excitonic state of DPA followed the diffusion-assisted resonance energy transfer (RET) model. On the other hand, the excimer state showed negligible diffusion and energy transfer from this state found to follow the single-step Förster resonance energy transfer mechanism. The observation of efficient white light emission in the doped DPA nanoaggregates was proposed to have prospective applications in OLED devices, given the fact that triplet excitons may be exploited for emission through the efficient triplet-triplet annihilation contribution to fluorescence enhancement.

Broadband white-light emission from supramolecular piperazinium-based lead halide perovskites linked by hydrogen bonds

We demonstrate white-light emission using lead halide perovskites: (pip)2PbBr6 (pip = piperazine), (pip)2Pb4Cl12, (1mpz)2PbBr6 (1mpz = 1-methylpiperazine), and (2,5-dmpz)0.5PbBr3·2((CH3)2SO) (2,5-dmpz = trans-2,5-dimethylpiperazine, abbreviated as (2,5-dmpz)0.5PbBr3), in which the inorganic frameworks were connected by piperazinium dications through hydrogen bonds, forming a three-dimensional supramolecular network. From single-crystal X-ray diffraction measurements and Raman spectroscopy, we identified the crystal structures and local environmental vibrational modes in the inorganic framework, finding that (pip)2PbBr6 crystallized in the centrosymmetric orthorhombic space group Pnnm, whereas (pip)2Pb4Cl12 crystallized in the trigonal/rhombohedral space group R3. The zero-dimensional (1mpz)2PbBr6 structure crystallized in the centrosymmetric monoclinic space group P2/n, whereas the [PbBr6]4- octahedron was separated by a 1-methylpiperazine dication. (2,5-dmpz)0.5PbBr3·2((CH3)2SO) contained half a cation, which was completed by inversion symmetry, along with two dimethyl sulfoxide solvent molecules that crystallized in the monoclinic space group P21/c. Among the perovskites, (2,5-dmpz)0.5PbBr3·2((CH3)2SO) exhibited the longest carrier lifetime (42 ns), the lowest band gap (2.34 eV), and the highest photoluminescence quantum yield (58.02%). This is because it forms a 1D corner-sharing structure and has localized electronic states near the conduction band minimum, which contributes to the high photoluminescence quantum yield and white-light emission.

White-Light Emission from a Semi-Conductive Borate-Stannate

In response to ever-increasing application requirements in lighting and displays, a tremendous emphasis is being placed on single-component white-light emission. Single-component inorganic borates doped with rare earth metal ions have shown prominent achievements in white-light emission. The first environmentally friendly defect-induced white-light emitting crystalline inorganic borate, Ba₂ [Sn(OH)₆ ][B(OH)₄ ]₂ , has been prepared. Additionally, it is the first borate-stannate without a Sn-O-B linkage. Notably, Ba₂ [Sn(OH)₆ ][B(OH)₄ ]₂ shows Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of (0.42, 0.38), an ultrahigh color rendering index (CRI) of 94.1, and an appropriate correlated color temperature (CCT) of 3083 K. Such a promising material will provide a new approach in the development of white-light emitting applications.

White Light Emission from a Simple Mixture of Fluorescent Organic Compounds

Three fluorescent organic compounds—furocoumarin (FC), dansyl aniline (DA), and 7-hydroxycoumarin-3-carboxylic acid (CC)—are mixed to produce almost pure white light emission (WLE). This novel mixture is immobilised in silica aerogel and applied as a coating to a UV LED to demonstrate its applicability as a low-cost, organic coating for WLE via simultaneous emission. In ethanol solution and when immobilised in silica aerogel, the mixture exhibits a Commission Internationale d’Eclairage (CIE) chromaticity index of (0.27, 0.33). It was observed that a broadband and simultaneous emission involving coumarin carboxylic acid, furocoumarin and dansyl aniline played a vital role in obtaining a CIE index close to that of pure white light.

Photoresponsive sulfone-based molecules: photoinduced electron transfer and heat/air-stable radicals in the solid state

Photoinduced electron transfer (PET) of two sulfone-based molecules with the formation of stable radicals was observed for the first time in the solid state.

Utilizing an effective framework to dye energy transfer in a carbazole-based metal–organic framework for high performance white light emission tuning

By introducing dyes into a MOF, a white-light-emitting luminophor was obtained based on effective framework to dye energy transfer mechanism.