Light Emission Properties Research Articles

Pentacyclic fused diborepinium ions with carbene- and carbone-mediated deep-blue to red emission.

Designing molecules that can undergo late-stage modifications resulting in specific optical properties is useful for developing structure-function trends in materials, which ultimately advance optoelectronic applications. Herein, we report a series of fused diborepinium ions stabilized by carbene and carbone ligands (diamino-N-heterocyclic carbenes, cyclic(alkyl)(amino) carbenes, carbodicarbenes, and carbodiphosphoranes), including a detailed bonding analysis. These are the first structurally confirmed examples of diborepin dications and we detail how distortions in the core of the pentacyclic fused system impact aromaticity, stability, and their light-emitting properties. Using the same fused diborepin scaffold, coordinating ligands were used to dramatically shift the emission profile, which exhibit colors ranging from blue to red (358-643 nm). Notably, these diborepinium ions access expanded regions of the visible spectrum compared to known examples of borepins, with quantum yields up to 60%. Carbones were determined to be superior stabilizing ligands, resulting in improved stability in the solution and solid states. Density functional theory was used to provide insight into the bonding as well as the specific transitions that result in the observed photophysical properties.

Preparation of seven-coordinated hypervalent tin(IV)-fused azobenzene and applications for stimuli-responsive π-conjugated polymer films.

Heavy atoms can form highly coordinated states, and their optical properties have attracted much attention. Recently, we have demonstrated that a reversible coordination-number shift of hypervalent tin(IV) from five to six can provide predictable hypsochromic shifts in light absorption and emission properties in small molecules and a π-conjugated polymer film. Herein, we show the preparation of seven-coordinated tin and reveal that the binding constant of the seven coordination with ethylenediamine (EDA, K = 2900 M-1) is 200 times higher than that of six coordination with propylamine (PA, K = 14 M-1) owing to the chelate effect. Moreover, reversible vapochromism of the π-conjugated polymer film was observed upon exposure (λabs = 598 nm and λPL = 697 nm) and desorption (λabs = 641 nm and λPL = 702 nm) of EDA vapor. Furthermore, as a unique demonstration, the thermochromic film was prepared by fixing the seven coordination as the initial state using 1,10-phenanthroline. These optical variations are predictable by quantum chemical calculations. Our findings are valuable for the development of designable and controllable stimuli-responsive materials focusing on the inherent properties of the elements.

Quantum engineering of the radiative properties of a nanoscale mesoscopic system.

Despite the recent advances in quantum technology, the problem of controlling the light emission properties of quantum emitters used in numerous applications remains: a large spectral width, low intensity, blinking, photodegradation, biocompatibility, etc. In this work, we present the theoretical and experimental investigation of quantum light sources - mesoscopic systems consisting of fluorescent molecules in a thin polydopamine layer coupled with metallic or dielectric nanoparticles. Polydopamines possess many attractive adhesive and optical properties that promise their use as host media for dye molecules. However, numerous attempts to incorporate fluorescent molecules into polydopamines have failed, as polydopamine has been shown to be a very efficient fluorescence quencher through Förster resonance energy transfer and/or photoinduced electron transfer. Using the system as an example, we demonstrate new insights into the interactions between molecules and electromagnetic fields by carefully shaping its energy levels through strong matter-wave coupling of molecules to metallic nanoparticles. We show that the strong coupling effectively suppresses the quenching of fluorescent molecules in polydopamine, opening new possibilities for imaging.

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.

Azacoumarin-based "turn-on" fluorescent probe for the detection and imaging of hydrogen peroxide in living cells.

Azacoumarins are a relatively unexplored group of coumarin fluorophores, despite their excellent light-emitting properties. In this report, we detail the creation and production of a fluorescent probe (PYCB) based on azacoumarin for detecting H2O2. The probe utilizes a carboxy benzyl boronic pinacol ester as the recognition unit and displays a turn-on fluorescence response at 460 nm upon exposure to H2O2. The probe shows excellent sensitivity and selectivity to H2O2, with a detection limit of 0.385 μM. PYCB also exhibited strong pH stability and selectivity for H2O2 over other reactive oxygen species (ROS). Additionally, MTT assay results demonstrated the excellent biocompatibility of PYCB in MCF-7 cell lines. Fluorescence imaging of PYCB-treated MCF-7 cells revealed enhanced blue fluorescence corresponding to varying concentrations of exogenous H2O2.

Optical gain and entanglement through dielectric confinement and electric field in InP quantum dots.

Quantum dots are widely recognized for their advantageous light-emitting properties. Their excitonic fine structure along with the high quantum yields offers a wide range of possibilities for technological applications. However, especially for the case of colloidal QDs, there are still characteristics and properties which are not adequately controlled and downgrade their performance for applications which go far beyond the simple light emission. Such a challenging task is the ability to manipulate the energetic ordering of exciton and biexciton emission and subsequently control phenomena such as Auger recombination, optical gain and photon entanglement. In the present work we attempt to engineer this ordering for the case of InP QDs embedded in polymer matrix, by means of their size, the dielectric confinement and external electric fields. We employ well tested, state of the art theoretical methods, in order to explore the conditions under which the exciton-biexciton configuration creates the desired conditions either for optical gain or photon entanglement. Indeed, this appears to be feasible for QDs with small diameters (1 nm, 1.5 nm) embedded in a host material with high dielectric constant and additional external electric fields. These findings offer a new design principle which might be complementary to the well-established type II core-shell QDs approach for achieving electron-hole separation.

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

Light emission from group-IV based nanostructures has been attracting much attention in the field of Si-based photonics because of its potential to combine photonic processing with electronic processing on a single chip [1]. Among various Fe-silicides, semiconducting β-FeSi2 shows light emission in the near-infrared region [2, 3] and is one of promising materials in optoelectronic application from viewpoints of tuning emission energy and improving luminous efficiency by means of quantized structures. In this work, we focus on low temperature formation of β-FeSi2 nanodots (NDs) over ~1011 cm-2 in areal density on SiO2 and the characterization of light emission properties of β–FeSi2 NDs.After conventional wet-chemical cleaning steps of p-type Si(100) substrates, a ~300-nm-thick SiO2 layer was grown at 1000°C in dry O2 and followed by dipping shortly in a dilute HF solution to make uniform surface termination with Si-OH bonds. After that, Fe films in the thickness range from 1.0 to 3.0 nm were formed on the OH-terminate SiO2 layer by electron beam evaporation without any extra heating. And then, the Fe–films were exposed to remote plasma of pure H2 (H2-RP) at 400°C to form highly-dense Fe-NDs [4]. Subsequently, so-prepared Fe-NDs were exposed to pure SiH4 at 400°C while controlling the amount of SiH4 exposure by duration and pressure.AFM images taken after exposure of Fe-films to H2-RP confirm the high-density formation of well-defined NDs. In the cases of H2-RP exposure of 1.3-nm-thick and 3.0-nm-thick Fe-films, the areal dot densities as high as ~1.1 × 1011 and ~1.3 × 1011 cm−2 were obtained, respectively, in which the average dot-heights of self-assembled Fe-NDs were determined to be ~5.3 and ~10.9 nm, respectively, by fitting a log-normal function to each measured size distribution. Notice that AFM images taken after SiH4 exposure show almost no change in the areal dot density while a slight increase in the average dot height. From cross-sectional transmission electron microscope images, we have also verified the formation of distorted-spherical shape NDs with a lattice spacing of ~0.18 nm associated with β-FeSi2. And the result is well consistent with the chemical composition of NDs after SiH4 exposure as evaluated by x-ray photoelectron spectroscopy. In addition, with 976 nm light excitation using a semiconductor laser, the NDs after the SiH4 exposure show stable photoluminescence (PL) signals in the energy region from ~0.7 to ~0.9 eV even at room temperature. On the other hand, no PL signals were detected from the NDs before the SiH4 exposure and after Ar anneal at 400°C. Also, when the size of the Fe-silicide NDs was increased from ~5.3 to ~10.9 nm in average dot height by increasing the initial Fe-film thickness, a distinct red-shift in PL was clearly observed. Thus, the observed PL can be interpreted in terms of radiative recombination of photogenerated carriers through quantized states of β-FeSi2 NDs. These results indicate that SiH4 exposure to Fe-NDs formed on SiO2 is a very promising technique for the low-temperature fabrication of luminescent FeSi2 NDs.AcknowledgementThis work was supported in part by Grant-in-Aid for Scientific Research (A) 21H04559 of MEXT Japan, and the Cooperative Research Project Program of the Research Institute of Electrical Communication, Tohoku University.

Green approach for the fabrication of dual-functional S/N doped graphene tagged ZnO nanograins for in vitro bioimaging and water pollutant remediation

Dual-functional S/N (sulfur and nitrogen) doped graphene-tagged zinc oxide nanograins were synthesized for bioimaging applications and light-dependent photocatalytic activity. Applying the green synthesis approach, graphene was synthesized from kimchi cabbage through a hydrothermal process followed by tagging it with synthesized zinc oxide nanoparticles (ZnO-NPs). The 2D/0D heterostructure prepared by combining both exhibited exceptional advantages. Comprehensive characterizations such as TEM, SEM, XRD, FTIR, XPS, and UV–Vis spectra have been performed to confirm the structures and explore the properties of the synthesized nanocomposite. The graphene/ZnO-NP composite produced exhibited more intense fluorescence, greater chemical stability and biocompatibility, lower cytotoxicity, and better durability than ZnO NPs conferring them with potential applications in cellular imaging. While tagging the ZnO NPs with carbon derived from a natural source containing hydroxyl, sulfur, and nitrogen-containing functional group, the S/N doped graphene/ZnO heterostructure evidences the high photocatalytic activity under UV and visible irradiation which is 3.2 and 3.8 times higher than the as-prepared ZnO-NPs. It also demonstrated significant antibacterial activity which confers its application in removing pathogenic contaminant bacteria in water bodies. In addition, the composite had better optical properties and biocompatibility, and lower toxicity than ZnO NPs. Our findings indicate that the synthesized nanocomposite will be suitable for various biomedical and pollutant remediation due to its bright light-emitting properties and stable fluorescence.

Blue emitting exciplex for yellow and white organic light-emitting diodes

White organic light-emitting diodes (WOLEDs) have several desirable features, but their commercialization is hindered by the poor stability of blue light emitters and high production costs due to complicated device structures. Herein, we investigate a standard blue emitting hole transporting material (HTM) N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)benzidine (NPB) and its exciplex emission upon combining with a suitable electron transporting material (ETM), 3-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole (TAZ). Blue and yellow OLEDs with simple device structures are developed by using a blend layer, NPB:TAZ, as a blue emitter as well as a host for yellow phosphorescent dopant iridium (III) bis(4-phenylthieno[3,2-c]pyridinato-N,C2')acetylacetonate (PO-01). Strategic device design then exploits the ambipolar charge transport properties of tetracene as a spacer layer to connect these blue and yellow emitting units. The tetracene-linked device demonstrates more promising results compared to those using a conventional charge generation layer (CGL). Judicious choice of the spacer prevents exciton diffusion from the blue emitter unit, yet facilitates charge carrier transport to the yellow emitter unit to enable additional exciplex formation. This complementary behavior of the spacer improves the blue emission properties concomitantly yielding reasonable yellow emission. The overall white light emission properties are enhanced, achieving CIE coordinates (0.36, 0.39) and color temperature (4643 K) similar to daylight. Employing intermolecular exciplex emission in OLEDs simplifies the device architecture via its dual functionality as a host and as an emitter.Graphical abstract

Enhancing Multiexcitonic Emission in Metal-Halide Perovskites by Quantum Confinement.

Semiconductor metal halide perovskite nanocrystals have been under intense investigation for their promise in a variety of optoelectronic applications, which arises from their remarkable properties of defect tolerance and efficient light emission. Recently, quantum dot versions of perovskite nanocrystals have been available, enabling investigation of how quantum size effects control optical function and performance in these quantum dots (QD), past their well-known covalent II-VI analogues. We perform time-resolved photoluminescence (t-PL) experiments on CsPbBr3 perovskite nanocrystals spanning in diameter from 5.8 nm strongly confined quantum dots to 18 nm weakly confined quantum dots. Experiments are performed with sufficient time resolution of 3 ps to observe the interaction energies and recombination kinetics from excitons to multiexcitons. Comparing the same sized QD reveals that perovskite QD have a larger radiative rate constant for emission from X than CdSe QD due to a larger oscillator strength. The multiexciton (MX) regime reveals that perovskite QD emit brightly and with more focused bandwidth than equivalent sized CdSe QD enabling more spectrally pure brightness. The MX kinetics reveals that the perovskite QD maintain efficient radiative decay, effectively competing with Auger recombination. These experiments reveal that the strongly confined QD of perovskites can be efficient multiexcitonic emitters, such as in high brightness light emitting diodes, especially in the blue.

Sensitive Detection of Trace Explosives by a Self-Assembled Monolayer Sensor.

Fluorescence probe technology holds great promise in the application of trace explosive detection due to its high sensitivity, fast response speed, good selectivity, and low cost. In this work, a designed approach has been employed to prepare the TPE-PA-8 molecule, utilizing the classic aggregation-induced emission (AIE) property of 1,1,2,2-tetraphenylethene (TPE), for the development of self-assembled monolayers (SAMs) targeting the detection of trace nitroaromatic compound (NAC) explosives. The phosphoric acid acts as an anchoring unit, connecting to TPE through an alkyl chain of eight molecules, which has been found to play a crucial role in promoting the aggregation of TPE luminogens, leading to the enhanced light-emission property and sensing performance of SAMs. The SAMs assembled on Al2O3-deposited fiber film exhibit remarkable detection performances, with detection limits of 0.68 ppm, 1.68 ppm, and 2.5 ppm for trinitrotoluene, dinitrotoluene, and nitrobenzene, respectively. This work provides a candidate for the design and fabrication of flexible sensors possessing the high-performance and user-friendly detection of trace NACs.

Dipolar 1,3,6,8-tetrasubstituted pyrene-based emitters containing hole- and electron-transporting moieties: Syntheses, structures, optical properties, electrochemistry and electroluminescence

A series of dipolar 1,3,6,8-tetrasubstituted pyrene-based compounds (PyTPA, PyCaZ and Py3CaZ) with a D-π-A configuration were designed and synthesized. The characteristic of these report compounds is that the pyrene core possesses two electron-transporting benzimidazole moieties at 1,8-positions and two hole-transporting arylamine segments at 3,6-sites. These compounds were structurally characterized and their photoelectric properties were investigated by spectroscopy, electrochemical and theoretical studies. The intermolecular π-π interactions successfully suppressed in these polysubstituted pyrenes, which leads to relatively high absolute fluorescence quantum efficiencies in film state (73.89–85.74 %). These three compounds exhibit high thermal stability with their decomposition temperature up to 520 °C. Two types of solution-processing devices were fabricated using compounds PyTPA and Py3CaZ as representatives to investigate their electron-transporting, hole-transporting and light-emitting properties. The single layer device based on PyTPA exhibits a current efficiency of 8.02 cd/A and a maximum brightness of 24439 cd/m2 at 7.8 V.

Crystal Structure, Quantum Chemical, Hirshfeld Surface and Molecular Docking of Organic Molecular Salt: 2‐Amino‐5‐Chloropyridinium‐2,4‐Dihydroxybenzoate

AbstractAn organic molecular salt, 2‐amino‐5‐chloropyridinium‐2,4‐dihydroxybenzoate (ACP‐DHB) is synthesized by the slurry method followed by crystallization from methanol. The formation of molecular salt is initially confirmed by 1H and 13C nuclear magnetic resonance (NMR) spectral data. Single crystal X‐ray diffraction (XRD) analysis shows that the crystal belongs to the monoclinic crystal system with space group, P21/n. Further, the supramolecular assembly involved the extensive network of N+−H···O− and N−H···O hydrogen bonds as well as C‐Cl···O halogen bond. Using UV‐Visible spectral data, the optical band gap is calculated and found to be 4.21 eV. Photoluminescence studies indicate the crystal has blue light emission properties. TG/DTA analysis shows that ACP‐DHB is thermally stable up to 162 °C. The quantum chemical calculations and natural bond analysis (NBO) are performed at B3LYP/6‐311G++ (d,p) basis set using Gaussian 09 software. The relative contributions of various intermolecular connections are discussed using Hirshfeld surface analysis and fingerprint plot illustration. The antibacterial and antifungal activity exhibits better inhibitory capacity against pathogens. Molecular docking revealed that ACP‐DHB efficiently binds with the 1UAG and 5KEE targets and has strong binding ability to the proteins. ADMET factors and Lipinski's rule of five are used to predict drug likeness property.

Manipulating Lone-Pair-Driven Luminescence in 0D Tin Halides by Pressure-Tuned Stereochemical Activity from Static to Dynamic.

The excellent luminescence properties and structural dynamics driven by the stereoactivity of the lone pair in a variety of low-dimensional ns2 metal halides have attracted growing investigations for optoelectronic applications. However, the structural and photophysical aspects of the excited state associated with the lone pair expression are currently open questions. Herein, zero-dimensional Sn-based halides with static stereoactive 5 s2 lone pairs are selected as a model system to understand the correlations between the distinctive lone pair expression and the excited-state structural relaxation and charge carrier dynamics by continuous lattice manipulation. Lattice compression drives 5 s2 lone pair active switching and self-trapped exciton (STE) redistribution by suppressing excited-state structural deformation of the isolated SnBr4 2- units. Our results demonstrate that the static expression of the 5 s2 lone pair results in a red broadband triplet STE emission with a large Stokes shift, while its dynamic expression creates a sky-blue narrowband emission dominated by the radiative recombination of singlet STEs. Our findings and the photophysical mechanism proposed highlight the stereochemical effects of lone pair expression in controlling light emission properties and offer constructive guidelines for tuning the optoelectronic properties in diverse ns2 metal halides.

Asymmetrical liquid crystals synthesis for effective sensing: Fluorescence investigations

Currently, a new set of asymmetrical dimeric molecules with a Schiff-base at one end and a chalcone alkali substitution by di-ether are made and their liquid crystal and fluorescence properties are investigated. The proposed chemical structure was confirmed by routine analytical methods using FT-IR and NMR spectroscopy. Additionally, polarized optical microscopy (POM); was used to assess the pointed compounds' liquid crystalline characteristics, while differential scanning calorimetry (DSC); was employed to confirm the compounds' transitions. The results report the length of the alkali chain at one end of the molecule is critical to the creation of the mesophase type. Compounds with medium-length chains exhibit nematic mesophases with moderate transition temperatures. The fluorescence of compounds was analyzed, with blue-emitting results indicating the presence of blue-light-emitting features. The 10a had higher ɛ; as well as red-shifted λmax; and Fmax; compared to the others and has blue light emission properties. Eventually; the expanding range of possible uses to include OLED material and fluorescent probes for sensing applications.

Manipulating Lone‐Pair‐Driven Luminescence in 0D Tin Halides by Pressure‐Tuned Stereochemical Activity from Static to Dynamic

AbstractThe excellent luminescence properties and structural dynamics driven by the stereoactivity of the lone pair in a variety of low‐dimensional ns2 metal halides have attracted growing investigations for optoelectronic applications. However, the structural and photophysical aspects of the excited state associated with the lone pair expression are currently open questions. Herein, zero‐dimensional Sn‐based halides with static stereoactive 5 s2 lone pairs are selected as a model system to understand the correlations between the distinctive lone pair expression and the excited‐state structural relaxation and charge carrier dynamics by continuous lattice manipulation. Lattice compression drives 5 s2 lone pair active switching and self‐trapped exciton (STE) redistribution by suppressing excited‐state structural deformation of the isolated SnBr42− units. Our results demonstrate that the static expression of the 5 s2 lone pair results in a red broadband triplet STE emission with a large Stokes shift, while its dynamic expression creates a sky‐blue narrowband emission dominated by the radiative recombination of singlet STEs. Our findings and the photophysical mechanism proposed highlight the stereochemical effects of lone pair expression in controlling light emission properties and offer constructive guidelines for tuning the optoelectronic properties in diverse ns2 metal halides.

Aggregation-induced electrochemiluminescence enhancement of Ag-MOG for amyloid β 42 sensing

This study aimed to introduce an immunosensor for measuring amyloid β 42 (Aβ42) levels by aggregation-induced enhanced electrochemiluminescence (ECL). Metal–organic gels (MOGs) are novel soft materials with advantages such as high gel stability, good light-emitting properties, and easy preparation. This study used silver nanoparticle metal–organic gel (Ag-MOG) as a substrate to connect Aβ42-Ab2 and the cathodoluminescent probe. Potassium persulfate was used as a co-reactant that could emit a high ECL signal. CuS@Au had the benefits of a relatively large surface area with excellent carrier function; therefore, it was used as a substrate to load a large amount of Aβ42-Ab1, significantly improving the immunosensor sensitivity. The ECL intensity of Aβ42 was linear in the range of 0.01 pg/mL to 250 ng/mL with a detection limit of 2.2 fg/mL (S/N = 3) under optimized detection conditions. This ECL immunosensor has been successfully applied to detect Aβ42 in human serum with the advantages of excellent stability and high selectivity. This method not only expands the potential applications of ECL immunosensors based on biological testing and clinical diagnosis but also provides a viable approach to basic clinical testing.

Characterization of YAG:Ce ceramics with graphene oxide

Yttrium-aluminum garnet (Y3Al5O12) is an optical material that shows great potential due to its favorable light-emitting and mechanical properties, as well as its chemical stability and thermal resistance. It is commonly utilized in laser technology, optical instruments, and solid-state light sources as a result of its activation by transition metal or rare earth element ions. In this work, experiments were carried out on the procedure for compacting samples of luminescent ceramics Y3Al5O12:Ce3+, by single-base pressing followed by sintering. Comprehensive studies of the influence of graphene oxide of variable concentration (x=0.1;0.5; 1 wt.%) on the radiative characteristics of ceramic samples. It was found that the addition of graphene oxide in an amount from 0.1 to 1 wt. % affects the density and luminescent properties of YAG:Ce ceramics. There is a decrease in the value of the density parameter at concentrations of graphene oxide 0.1-1 wt. % before annealing, after annealing, the relative density value increases to ~99 %. The luminescence spectrum when excited by a blue LED chip appears as a wide band in the spectral range 460-750, the nature of which is associated with radiative transitions in the cerium ion. It has been established that the light-emitting characteristics have a downward trend when activated by graphene oxide. The integral luminescence intensity decreases from 27.1 % to 19 % with an increase in the concentration of graphene oxide.

(Invited) Coupled Quantum Emitters in Carbon Nanotubes

The development of covalent diazonium functionalization of carbon nanotubes brings unique opportunities in terms of original quantum sources of light. In particular, it should be possible to create a linear ensemble of closely packed single-photon sources along the carbon nanotube backbone. The physical proximity of several dopants would make it possible to couple them simultaneous to a resonant cavity mode and to induce original dynamics and light emission properties. Here, we investigate experimentally the case of a series of four quantum emitters attached to the same carbon nanotube coupled to a high finesse fiber cavity. We explore their properties through PLE, polarization and super-localization measurements and their light emission properties using time-correlation techniques and photo-luminescence decay measurements. We show that two pairs show qualitatively different behaviors in terms of spectral diffusion and luminescence saturation, which we interpret using two models of electronically coupled or uncoupled two-level systems.

(Invited) Effect of Cu Doping on the Energy Structure of Dumbbell-Shaped ZnS-AgInS2 Nanocrystals

Colloidal semiconductor nanocrystals (NCs) have been intensively developed for applications in photovoltaics, light-emitting diodes, electroluminescent devices, and biological markers, due to their tunable light absorption and excellent light emission properties. Among them, group I-III-VI-based multinary semiconductor NCs, such as CuInS2, CuInSe2 and AgInS2, have received significant attention for the application to solar energy conversion systems because of their large absorption coefficient and low toxicity. Recently, we have successfully prepared ZnS-AgInS2 solid solution (ZAIS) NCs and optimized their photocatalytic activity for hydrogen production by tuning their chemical composition, size and particle morphology.1-3 The photocatalytic activity of ZAIS NCs was further enhanced by the formation of a dumbbell structure that had a type-II heterojunction at the interface between the tip and rod parts of the NCs.4 In this study, to further improve the photocatalytic activity of dumbbell-shaped ZAIS NCs, we attempted to tune the energy structure of the heterojunction by Cu doping in tip parts for effective charge separation. Rod-shaped ZAIS NCs with sizes of 4.0 × 23 nm were prepared by the previously reported method.3 The crystal growth of tip parts was carried out by heating a mixture of rod-shaped ZAIS NCs, Cu(OAc), Ag(OAc), In(OAc)3, and thiourea in an organic solvent, in which rod-shaped ZAIS NCs acted as a nucleus to form tip parts composed of (Cu y Ag(1-y)In) x Zn2(1-x)S2 solid solution. Thus-obtained dumbbell-shaped NCs were isolated from the resulting solution via size-selective precipitation. The amount of Cu doping in tip parts was controlled by changing the Cu content in metal precursors. TEM observations showed that obtained NCs had a dumbbell structure regardless of the Cu content in the metal precursor. Ellipsoidal NCs with sizes of 5.6 × 11 nm were deposited on both tips of rod-shaped ZAIS NCs. The absorption onset of the dumbbell-shaped NCs were red-shifted from 650 nm to 850 nm with an increase in the Cu fraction from y = 0 to 0.75. The photoelectron yield spectroscopy revealed that the conduction band minimum level was constant at ca. -3.2 eV, while the valence band maximum level was gradually shifted from -5.1 eV to -4.8 eV as the Cu fraction in tip parts increased from y = 0 to 0.75. Thus, it is concluded that the absorption property of dumbbell-shaped ZAIS NCs could be successfully extended from the visible to the near-IR region without changing the energy of photogenerated electrons, simply by modulating the degree of Cu doping in the tip parts. This tunability is useful for constructing efficient solar-light-driven photocatalysts for H2 evolution. T. Torimoto, T. Adachi, K. Okazaki, M. Sakuraoka, T. Shibayama, B. Ohtani, A. Kudo, S. Kuwabata, J. Am. Chem. Soc., 129 (2007) 12388-12389.T. Kameyama, T. Takahashi, T. Machida, Y. Kamiya, T. Yamamoto, S. Kuwabata, T. Torimoto, J. Phys. Chem. C, 119 (2015) 24740-24749.T. Torimoto, Y. Kamiya, T. Kameyama, H. Nishi, T. Uematsu, S. Kuwabata, T. Shibayama, ACS Appl. Mater. Inter., 8, (2016) 27151-27161.T. Kameyama, S. Koyama, T. Yamamoto, S. Kuwabata, T. Torimoto, J. Phys. Chem. C, 122 (2018) 13705-13715.