Introduction Of Tert-butyl Groups Research Articles

Towards Efficient Blue Delayed-Fluorescence Molecules by Modulating Torsion Angle Between Electron Donor and Acceptor

Towards Efficient Blue Delayed-Fluorescence Molecules by Modulating Torsion Angle Between Electron Donor and Acceptor

Realizing performance improvement of borylated TADF materials for OLEDs

A series of green to blue-emitting thermally activated delayed fluorescence (TADF) molecules (m-B-D series) centered on three-coordinated boron were designed and synthesized, denoted as m-B-PTZ, m-B-PXZ, m-B-DMAC, and m-B-SAC. Triarylborane was used as the acceptor and four different acridan derivatives were used as donors, i.e., phenothiazine, phenoxazine, dimethylacridine, and spiroacridine, to form a donor-acceptor configuration. The introduction of tert-butyl group with greater steric hindrance on the bridged benzene led to a more thermally stable architecture. In addition, the spatially constrained molecular design causes the electron donors and electron acceptors in the molecule to approach each other perpendicularly, resulting in a small energy gap between the singlet and triplet excited state. In addition, the additional tert-butyl group reduced the photoisomerization caused by the auxiliary donor, thereby preventing energy quenching and improving the photoluminescence quantum yield. Consequently, the devices obtained using m-B-DMAC as the TADF emitter exhibited an emission wavelength of 480 nm and the maximum external quantum efficiency (EQE) of 14.3%, as well as an extremely low turn-on voltage of 2.9 V. The blue-emitting devices obtained using m-B-SAC demonstrated an emission wavelength of 471 nm and the peak EQE of 12.2%. Furthermore, m-B-PTZ and m-B-PXZ both correspond to green-emitting devices, showing EQEs of 14.0 and 10.1%, respectively. This improvement in thermal stability, emission color, and efficiency indicates that our molecular designs are promising strategies for obtaining borylated TADF-organic light-emitting diodes with outstanding electroluminescent performances.

Synthesis of meso-Alkyl-Substituted Norcorrole-NiII Complexes and Conversion to 5-Oxaporphyrins(2.0.1.0).

The synthesis of antiaromatic NiII -norcorroles having primary, secondary, and tertiary alkyl groups at the reactive meso-positions was attempted. Reductive coupling of a NiII -dipyrrin precursor provided NiII -meso-dihexylnorcorrole, which underwent substantial degradation on silica gel. Introduction of tert-butyl groups was unsuccessful due to the difficult preparation of the corresponding dipyrrin precursor. Meanwhile, NiII -norcorroles with isopropyl and cyclohexyl groups were isolated as stable molecules under ambient conditions. Furthermore, we found that oxidation of NiII -meso-dialkylnorcorroles with hydrogen peroxide in the presence of sodium carbonate gave NiII -5-oxaporphyrins(2.0.1.0). In contrast, oxidation of NiII -meso-dimesitylnorcorrole under the same reaction conditions gave 10-oxaporphyrin(1.1.1.0). The contrasting reactivity can be attributed to the steric congestion around the meso-positions.

Synthesis and characterization of poly(pyridine–imide)s with tert-butyl substituents

The aromatic diamine monomer containing a pyridine heterocyclic group and a tert-butyl substituent, 4-[(4′- tert-butyl)phenyl]-2,6-bis(4-aminophenyl)pyridine (BPAP), was successfully synthesized by a modified Chichibabin reaction of 4-nitro-acetophenone and 4- tert-butyl benzaldehyde, followed by a reduction of the resulting dinitro compound 4-[(4′- tert-butyl)phenyl]-2,6-bis(4-nitrophenyl)pyridine with palladium/carbon and hydrazine monohydrate, successively. A series of poly(pyridine–imide)s were prepared from the diamine BPAP with the alicyclic anhydride 1,2,3,4-cyclobutanetetracarboxylic dianhydride, aromatic anhydride pyromelitic dianhydride, 3,3′,4,4′-biphenyl tetracarboxylic dianhydride, and 4,4′-oxydiphthalic anhydride in N, N-dimethylformamide (DMF) via the conventional two-step method and further chemical imidization to obtain poly(pyridine-imide) powders. Due to the introduction of tert-butyl group, the polyimides (PIs) derived from BPAP were amorphous and displayed good solubility in amine-type polar solvents, such as DMF, dimethyl sulfoxide, N, N-dimethylacetamide, and N-methyl-2-pyrrolidone. Because of the presence of rigid triphenylpyridine units and bulky substituents, the final PIs held a good thermal stability with 10% weight loss temperatures above 504°C and left more than 55% residue even at 700°C under nitrogen atmosphere. The effect of tert-butyl substituents on the properties of the PIs was studied by comparing with 4-phenyl-2,6-bis(4-nitrophenyl)pyridine. These PIs exhibited some fluorescent properties because of the triphenylpyridine units, and the chemical structure of dianhydrides took an effect on the fluorescent property of these PIs.

Organic Dyes Containing Carbazole as Donor and π-Linker: Optical, Electrochemical, and Photovoltaic Properties

A series of new metal free organic dyes containing carbazole as donor and π-linker have been synthesized and characterized as effective sensitizers for dye sensitized solar cells (DSSCs). The carbazole functionalized at C-2 and C-7 served as electron-rich bridge. The donor property of the carbazole is substantially enhanced on introduction of tert-butyl groups at C-3 and C-6 positions and the oxidation propensity of the dyes increased on insertion of thiophene unit in the conjugation pathway. These structural modifications fine-tuned the optical and electrochemical properties of the dyes. Additionally, the presence of tert-butyl groups on the carbazole nucleus minimized the intermolecular interactions which benefited the performance of DSSCs. The dyes served as efficient sensitizers in DSSCs owing to their promising optical and electrochemical properties. The efficiency of DSSCs utilizing these dyes as sensitizers ranged from 4.22 to 6.04%. The tert-butyl groups were found to suppress the recombination of injected electrons which contributed to the increment in the photocurrent generation (JSC) and open circuit voltage (VOC). A dye with carbazole donor functionalized with tert-butyl groups and the conjugation bridge composed of 2,7-disubstituted carbazole and thiophene fragments exhibited higher VOC value. However, the best device efficiency was observed for a dye with unsubstituted carbazole donor and the π-linker featuring carbazole and bithiophene units due to the high photocurrent generation arising from the facile injection of photogenerated electrons into the conduction band of titanium dioxide (TiO2) facilitated by the low-lying LUMO.

New efficient dyes containing tert-butyl in donor for dye-sensitized solar cells

A series of D–π–A organic sensitizers that contains two 4-tert-butylbenzene moieties in the donor part of triphenylamine group are designed and characterized. All these dyes comprise the same donor and acceptor units while the different aromatic units are introduced as linkers between the donor and acceptor units. It is found that the tuning of the HOMO and LUMO energy level can be conveniently achieved by alternating the conjugate bridge. The DSSCs based on LI-17 show the best light to electricity conversion efficiency of 5.35% (Jsc = 12.65 mA cm−2, Voc = 675 mV, ff = 0.63) under standard global AM 1.5 solar light conditions (100 mW cm−2), indicating that the introduction of tert-butyl groups may be able to play an anti-aggregation effect.

Stabilization of organic field-effect transistors by tert-butyl groups in dibenzotetrathiafulvalene derivatives

For a material for organic thin-film transistors, not only high mobility but also low threshold voltage and long-term stability are important requirements. In order to realize these properties, materials with relatively large oxidation potentials, namely weak donors, have been designed as p-channel organic semiconductors. Here we propose a different strategy; transistor properties of dibenzotetrathiafulvalene (DBTTF) are significantly improved by the introduction of tert-butyl groups. Although this chemical modification does not much change the ionization potential, small threshold voltage and stability over several months are attained together with the improved mobility, probably due to some kind of passivation effect of the bulky tert-butyl groups. In contrast, the systematic fluorine substitution rapidly diminishes the transistor performance. There are two kinds of herringbone structures with much different dihedral angles of about 50° and 130°, and the tert-butyl compound falls into the former category.

Mono- and dinuclear Pd(II) complexes of different salicylaldimine ligands as catalysts of transfer hydrogenation of nitrobenzene with cyclohexene and Suzuki–Miyaura coupling reactions

In this study, the synthesis, spectroscopic, catalytic, and electrochemical properties of salicylaldimine Schiff-base ligands ( L n ) and their dinuclear Pd(II) complexes for L 1 and L 2 ligands with mononuclear Pd(II) complexes for L 3 and L 4 ligands were investigated. The ligands and their mono- or dinuclear Pd(II) complexes were characterized by FT-IR, UV–Vis, 1H NMR and elemental analysis, as well as through magnetic susceptibility and spectroelectrochemical techniques. The catalytic studies showed that the introduction of tert butyl groups on the salicyl ring of the molecules increased the catalytic activity towards hydrogenation of nitrobenzene and cyclohexene in DMF at 25 and 45 °C. It was also observed that the steric hindered mono- and dinuclear Pd(II) complexes were thermally stable complexes and were not sensitive to air or the moisture. The complexes were easily prepared from cheap materials that could be used as versatile and efficient catalysts for different C–C coupling reactions (Suzuki–Miyaura reactions).

Total Synthesis of (±)‐Quadrangularin A

The key to successful coupling in the synthesis of (±)-quadrangularin A (1) was the introduction of tert-butyl groups in the precursor to block two reactive positions. Thus, the oxidative coupling of 3,5-di-(tert-butyl)resveratrol was carried out regioselectively in an efficient total synthesis of the natural product.

Novel Preorganized Hemispherands To Encapsulate Rare Earth Ions: Shielding and Ligand Deuteration for Prolonged Lifetimes of Excited Eu3+ Ions

Quenching of the luminescent excited state of Eu3+ ions by C-H high-vibrational modes was studied by deuteration of the encapsulating ligand and the solvent. Novel polydentate hemispherands providing nine donor atoms, which form overall neutral complexes with rare earth ions, were synthesized in nine steps, allowing the easy incorporation of deuterium atoms (11a-d·Eu3+). The introduction of tert-butyl groups at the aromatic rings of the ligand further increased the solubility of the complexes in organic solvents (29·Eu3+ and 34·Eu3+). Photophysical studies, viz., luminescence spectra and lifetime measurements, revealed that significant quenching of the Eu3+ excited state is induced by nearby C-H vibrational modes. Substitution of these quenching C-H modes for C-D bonds in the azacrown bridge leads to an enhancement of the luminescent lifetime by a factor of 1.5. C-H high-vibrational modes of the pendant arms which are at a larger distance to the Eu3+ ion than the azacrown bridge hydrogen atoms (determined from the MD calculations) are less efficient quenchers. The number of coordinating methanol molecules to 11a·Eu3+, 29·Eu3+, and 34·Eu3+ estimated by the Horrocks equation is 0.9, 1.2, and 1.9, respectively, as was predicted by MD calculations. Moreover, the experimental data show that quenching of the excited state of well-shielded Eu3+ ions by the C-H modes of the ligand is of the same order of magnitude as quenching by one O-H mode.

Relative stabilities of teramethoxycalix[4]arenes: combined NMR spectroscopy and molecular mechanics studies

Relative stabilities of four conformers and thermodynamic parameters for interconversion among four conformers of 25,26,27,28-tetramethoxycalix[4]arene (1a) and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetramethoxycalix[4]arene (1b) have been determined by 1H NMR spectroscopy. The relative stability of 1a is in the order partial cone (most stable) > cone > 1,2-alternate and 1,3-alternate (undetected) and that for 1b is in the order partial cone (most stable) > cone > 1,2-alternate > 1,3-alternate (least stable). These orders are reproduced well by MM3, in contrast with MM2. In particular, the energy differences between partial cones and cones computed by MM3 (0.27 kcal mol–1 for 1a and 1.50 kcal mol–1 for 1b) show good agreement with those determined by 1H NMR spectroscopy (0.32 ± 0.13 kcal mol–1 for 1a and 1.2 ± 0.3 kcal mol–1 for 1b). Both the computational and the spectroscopic results suggest that the basic skeletons for cones, 1,2-alternates and 1,3-alternates are relatively rigid (sharp potential energy surfaces) whereas that for partial cones is more or less flexible (flattened potential energy surface). Thus, introduction of the tert-butyl groups into the para-positions destabilizes cones and 1,2-alternates because it is difficult to reduce the increased steric crowding by the conformational change. In 1,3-alternates four phenol units are parallel, so that introduced tert-butyl groups would increase the steric crowding to a lesser extent. The basic skeleton for partial cones changes significantly upon introduction of tert-butyl groups, indicating that the increased steric crowding is relaxed by the conformational change. The finding clearly explains why partial cones frequently appear as the most stable conformer.