The time dependent density functional theory (TDDFT) and TDDFT/similarity transformed EOM domain-based local pair natural orbital CCSD (STEOM-DLPNO-CCSD) calculations were explored to estimate their ...validity in predicting the excited-state properties of multi-resonant thermally activated delayed fluorescence (MR-TADF) materials. Obviously, it was demonstrated that TDDFT calculation is inadequate to provide the quantitative prediction of the lowest singlet excited-state (S1), the lowest triplet excited-state (T1), and ΔEST. On the other hand, TDDFT/STEOM-DNLPNO-CCSD calculation reveals the superior prediction of S1, T1, and ΔEST that are in quantitative agreement with experiments. More importantly, it was found that TD-LC-⎤*HPBE/STEOM-DLPNO-CCSD calculation provides the most accurate prediction of S1, T1, and ΔEST. Accordingly, we suggest that TD-LC-⎤*HPBE/STEOM-DLPNO-CCSD calculation should be utilized to compute the excited-states properties of MR-TADF materials accurately.
•The pure TDDFT calculation is inadequate to calculate the S1, T1, and ⊗EST of MR-TADF materials quantitatively.•TDDFT/STEOM-DLPNO-CCSD calculation is advantageous to compute the S1, T1, and ⊗EST of MR-TADF materials quantitatively.•Particularly, TD-LC −⎤HPBE/STEOM-DLPNO-CCSD calculation reveals the most accurate prediction of S1, T1, and ⊗EST of MR-TADF materials rather than other TDDFT/STEOM-DLPNO-CCSD calculation.
We have studied the electrochemical and thermodynamic stability of Au(25)(SR)(18)(-), Au(38)(SR)(24), and Au(102)(SR)(44), R = CH(3), C(6)H(13), CH(2)CH(2)Ph, Ph, PhF, and PhCOOH, in order to examine ...ligand effects on the stability of thiol-stabilized gold nanoclusters, Au(m)(SR)(n). Aliphatic thiols, in general, have higher electrochemical and thermodynamic stability than aromatic thiols, and the -SCH(2)CH(2)Ph thiol is particularly appealing because of its high electrochemical and thermodynamic stability. The stabilization of Au(m) by nSR for Au(m)(SR)(n) can be rationalized by the stabilization of an Au atom by an SR for the simple molecule AuSR, regardless of interligand interaction and system size and shape. Thiol moieties play a strong role in the electron oxidation and reduction of Au(m)(SR)(n). Accounting for the characteristics of thiol ligands is essential for understanding the electronic and thermodynamic stability of thiol-stabilized gold nanoclusters.
Unusual stepwise increases of efficiency in fluorescent organic light-emitting diodes (OLEDs) was reported, which has not been observed in phosphorescent devices. However, the root cause of this ...phenomenon is unclear. Herein, we investigate the correlation between non-linear efficiency characteristics and the leakage current in conjunction with exciton formation in the electron blocking layer (EBL) as a function of voltage. Hole and electron transporting layers with different injection characteristics were selected to control the leakage current into the EBL. It was revealed that a significant amount of excitons were formed in the EBL. It was discovered that the degree of variation in the efficiency curve was directly related to the amount of leakage electrons from the emitting layer (EML) and the number of excitons in the EBL. Moreover, the exciton formation zone (EFZ) gradually shifted from the EBL into the EML as the voltage increased. After device degradation, the stepwise shape of the efficiency curves was significantly deformed, strongly implying that contributions to efficiency by excitons in the EBL vanished. Thus, the unusual stepwise increase in efficiency can be fully attributed to exciton formation in the EBL and shifting of the EFZ from the EBL to the EML.
A series of M-quinolate complexes were theoretically investigated to understand the effect of metal ions on electronic and charge transport properties by employing density functional theory ...simulation. It was found that both electronic and carrier transport properties in M-quinolate materials significantly depend on singly oxidized metal ions. In particular, Csq apparently showed an excellent advantage over other M-quinolate materials (M = Li, Na, K, Rb, Cs, Cu, Ag, and Au) in terms of electron mobility and injection. In addition, the dimerization and vertical detachment energies of all M-quinolate materials were compared to understand self-aggregation effect on carrier transport. As a result, it is expected that Csq is not only likely to be present in dimer form, but also reduce the density of electron traps in electron transporting materials.
Understanding the deterioration of the charge generation layer (CGL) is an uprising issue for efficient and stable tandem organic light-emitting diodes. Here, we comprehensively investigated the ...change in the electrical characteristics of Li-doped CGLs according to different stress conditions and compared the stability of Li diffusion in two phenanthroline-based electron transport materials. Through current density–voltage and capacitance-frequency measurements, it was revealed that electrical stress and thermal stress affect CGL’s electrical properties differently. Moreover, the exponential trap distribution model analysis informed that the Li diffusion is expedited toward narrowing depletion width in the CGL. Diffusion of Li and thermal effect to the diffusion was experimentally observed by X-ray photoelectron spectroscopy (XPS) depth profiling. We also evaluated variations in the operating voltage of tandem devices that differed only in nCGL. Overall, Li diffusion occurs more favorably in sparse Bphen film with weak binding energy rather than closely packed BPPB film with strong binding energy, which highlights that atomic geometry and morphological characteristics are crucial for the stability of tandem devices.
Highly efficient deep‐blue fluorescent materials based on phenylquinoline–carbazole derivatives (PhQ‐CVz, MeO‐PhQ‐CVz, and CN‐PhQ‐CVz) are synthesized for organic light‐emitting diodes (OLEDs). The ...materials form high‐quality amorphous thin films by thermal evaporation and the energy levels can be easily adjusted by the introduction of different electron‐donating and electron‐withdrawing groups on carbazoylphenylquinoline. Non‐doped deep‐blue OLEDs that use PhQ‐CVz as the emitter show bright emission (Commission Internationale de L'Éclairage (CIE) coordinates, x = 0.156, y = 0.093) with an external quantum efficiency of 2.45%. Furthermore, the material works as an excellent host material for 4,4′‐bis(9‐ethyl‐3‐carbazovinylene)‐1,1′‐biphenyl dopant to get high‐performance OLEDs with excellent deep‐blue CIE coordinates (x = 0.155, y = 0.157), high power efficiency (5.98 lm W−1), and high external quantum efficiency (5.22%).
Deep‐blue light‐emitting organic materials are still rare. Here, deep‐blue fluorescent emitters based on phenylquinoline–carbazole derivatives are synthesized for organic light‐emitting diodes (OLEDs). Multilayered OLEDs are fabricated with these materials as the emitting layer (non‐doped OLEDs) or as the host for BCzVBi dopant (doped OLEDs). The devices exhibit deep‐blue emission with high efficiencies (see figure).
There is an ongoing need for explosive detection strategies to uncover threats to human security including illegal transport and terrorist activities. The widespread military use of the explosive ...trinitrotoluene (TNT) for landmines poses another particular threat to human health in the form of contamination of the surrounding environment and groundwater. The detection of explosives, particularly at low picogram levels, by using a molecular sensor is seen as an important challenge. Herein, we report on the use of a fluorescent metal–organic framework hydrogel that exhibits a higher detection capability for TNT in the gel state compared with that in the solution state. A portable sensor prepared from filter paper coated by the hydrogel was able to detect TNT at the picogram level with a detection limit of 1.82 ppt (parts per trillon). Our results present a simple and new means to provide selective detection of TNT on a surface or in aqueous solution, as afforded by the unique molecular packing through the metal–organic framework structure in the gel formation and the associated photophysical properties. Furthermore, the rheological properties of the MOF‐based gel were similar to those of a typical hydrogel.
Sense and sensitivity on paper: A fluorescent metal–organic framework hydrogel exhibits greater detection capability for TNT in the gel state compared with that in the solution state. A portable sensor prepared from filter paper coated by the hydrogel was able to detect TNT at the picogram level with a detection limit of 1.82 ppt (parts per trillon; see figure).
Blue fluorescent materials based on silicone end‐capped 2‐diphenylaminofluorene derivatives are synthesized and characterized. These materials are doped into a 2‐methyl‐9,10‐di‐2‐naphthylanthracene ...host as blue dopant materials in the emitting layer of organic light‐emitting diode devices bearing a structure of ITO/DNTPD (60 nm)/NPB (30 nm)/emitting layer (30 nm)/Alq3 (20 nm)/LiF (1.0 nm)/Al (200 nm). All devices exhibit highly efficient blue electroluminescence with high external quantum efficiencies (3.47%–7.34% at 20 mA cm−2). The best luminous efficiency of 11.2 cd A−1 and highest quantum efficiency of 7.34% at 20 mA cm−2 are obtained in a device with CIE coordinates (0.15, 0.25). A deep‐blue OLED with CIE coordinates (0.15, 0.14) exhibits a luminous efficiency of 3.70 cd A−1 and quantum efficiency of 3.47% at 20 mA cm−2.
Highly efficient blue organic light‐emitting diodes are developed using dopant materials based on a 2‐diphenylaminofluoren‐7‐yl‐vinylarene core with various silicon‐substituted end‐capping groups. The best luminous efficiency of 11.2 cd A−1 and highest quantum efficiency of 7.34% at 20 mA cm−2 are obtained in a device with CIE coordinates (0.15, 0.25). A deep‐blue OLED with CIE coordinates (0.15, 0.14) exhibits a luminous efficiency of 3.70 cd A−1 and a quantum efficiency of 3.47% at 20 mA cm−2.
A new chromogenic chemosensor based on lysine-functionalized silver nanoparticles 1 was prepared and characterized by transmission electron microscopy (TEM), Fourier transform Raman, and ...ultraviolet−visible (UV−vis) spectroscopy. The color changes of nanoparticles 1 in the absence and the presence of metal ion were observed upon addition of various amino acids and proteins in aqueous solution. Among the various amino acids, the sensor 1 in the absence of metal ion shows a novel colorimetric sensor with capability to probe histidine and histidine-tagged proteins. On the other hand, the color changes of 1 in the presence of metal ions such as KCl or NiCl2 did not occur with any amino acids. Therefore, the sensor 1 in the absence of metal ion responds selectively to histidine, a response which can be attributed to its aggregation induced by histidine with high numbers of electrostatic interactions. This highly selective sensor 1 allows a rapid quantitative assay of histidine to concentrations as low as 5.0 μM, providing a new tool for the direct measurement of histidine and histidine-tagged proteins in vitro system. Furthermore, we examined the effect of pH on absorbance (A 520) of 1 in the presence of histidine (pH 4−12). The absorbance under basic conditions was higher than that under acidic or neutral conditions, in accord with the stronger aggregation of 1 with histidine by electrostatic interaction between the carboxylate anion of 1 and ammonium protons of histidine under basic conditions.
A series of new blue-emitting materials: 2-(10-(naphthalen-2-yl)anthracen-9-yl)pyridine (
1); 1-(10-(naphthalen-2-yl)anthracen-9-yl)isoquinoline (
2); ...9-(3-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl)-9H-carbazole (
3); 9-(4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl)-9H-carbazole (
4); 9-(4-(10-(naphthalen-1-yl)anthracen-9-yl)phenyl)-9H-carbazole (
5); 9-(4′-(10-(naphthalen-2-yl)anthracen-9-yl)biphenyl-4-yl)-9H-carbazole (
6); and 9-(4′-(10-(naphthalen-1-yl)anthracen-9-yl)biphenyl-4-yl)-9H-carbazole (
7) were designed and synthesized
via the Suzuki cross-coupling reaction. To explore the electroluminescent properties of these materials, multilayer OLEDs were fabricated in the following sequence: ITO/4,4′-bis(
N-(1-naphthyl)-N-phenylamino)biphenyl (NPB) (50
nm)/blue-emitting materials (
1–7) (30
nm) /4,7-diphenyl-1,10-phenanthroline (Bphen) (30
nm)/lithium quinolate (Liq) (2
nm)/Al (100
nm). Among those, a device using
6 as an emitter exhibited a high external quantum efficiency of 3.83% (3.20% at 20
mA/cm
2) with CIE coordinates of (0.152,
0.114). In order to improve EL efficiency,
1–7 were used as blue host materials for blue dopant materials 4′-2-(2-diphenylamino-9,9-diethyl-9H-fluoren-7-yl)vinyl-
p-terphenyl (
PFVtPh) and 3-(
N-phenylcarbazol)vinyl-
p-terphenyl (
PCVtPh). Using
1 as a host material for blue dopant material
PFVtPh, the resultant device showed high EL efficiencies with 10.35
cd/A, 8.77
lm/W, and 5.70% (10.24
cd/A, 6.06
lm/W, and 5.66% at 20
mA/cm
2). Furthermore, using
4 as a host for the
PCVtPh blue dopant, device
4c exhibited efficient deep-blue emissions with a maximum external quantum efficiency of 2.96% and CIE coordinates of (0.154,
0.087), very close to the NTSC blue standard of (0.14,
0.08).
