A new series of star‐shaped bipolar host molecules, tris(4′‐(1‐phenyl‐1H‐benzimidazol‐2‐yl)biphen‐yl‐4‐yl) amine (TIBN), tris(2′‐methyl‐4′‐(1‐phenyl‐1H‐benzimida zol‐2‐yl)biphenyl‐4‐yl)amine (Me‐TIBN), and tris(2,2′‐dimethyl‐4′‐(1‐phenyl‐1H‐benzimidazol‐2‐yl)biphenyl‐4‐yl)amine (DM‐TIBN), that contain hole‐transporting triphenylamine and electron‐transporting benzimidazole moieties are designed based on calculations using density functional theory and successfully prepared. The theoretical calculation of energy levels of TIBN derivatives affords helpful ideas to design molecules with a favorable localization of highest occupied/lowest unoccupied molecular orbital (HOMO/LUMO) levels and a predefined enhancement of the triplet energy gap. The TIBN derivatives are employed as hosts to fabricate phosphorescent organic light‐emitting diodes (OLEDs) by the two methods of spin‐coating and vacuum deposition. Notably, the spin‐coated Me‐TIBN and DM‐TIBN devices exhibit a much better performance than the vacuum‐deposited ones, in which the spin‐coated DM‐TIBN device (47 500 cd m−2, 27.3 cd A−1, 7.3 lm W−1) is outstanding with respect to other seminal work for solution‐processed OLEDs. More importantly, the new concept of localizing HOMO and LUMO levels for bipolar molecules is illustrated, and a facile strategy to tailor the energy levels by breaking the conjugation of hole‐ and electron‐transporting moieties is demonstrated.

Two solution-processible bipolar molecules, tris(3′-(1-phenyl-1H-benzimidazol-2-yl)biphenyl-4-yl)amine (TBBI) and tris(2-methyl-3′-(1-phenyl-1H-benzimidazol-2-yl)biphenyl-4-yl)amine (Me-TBBI), bearing both hole-transporting triphenylamine and electron-transporting benzimidazole moieties were newly prepared. TBBI and Me-TBBI possess excellent thermal stability with high glass-transition temperature (T g ) of 148 and 144 °C, and the decomposition temperatures (T d ) of 552 and 515 °C in nitrogen, respectively. They exhibit good solubility in common solvents due to the metastructured and star-shaped configuration allowing a solution processing. TBBI and Me-TBBI were employed to fabricate phosphorescent organic light-emitting diodes (OLEDs) as the host materials doped with the guest of Ir(ppy) 3 by spin coating with a single-layer structure. The solution-processed Me-TBBI device exhibited an improved performance relative to TBBI arising from the complete charge localization of HOMO and LUMO and an increase in the singlet-triplet (S 0 -T 1 ) energy gap. The performance of spin-coated Me-TBBI device (16400 cd m -2 , 27.4 cd A -1 , 4.5 lm W -1 ) is outstanding with respect to other work for fully solution-processed OLEDs with the similar single-layer structure.

Atomic-level visualization of the intercalation of layered materials, such as metal chalcogenides, is of paramount importance in the development of high-performance batteries. In situ images of the dynamic intercalation of Li ions into MoS2 single-crystal electrodes were acquired for the first time, under potential control, with the use of a technique combining laser confocal microscopy with differential interference microscopy. Intercalation proceeded via a distinct phase separation of lithiated and delithiated regions. The process started at the atomic steps of the first layer beneath the selvedge and progressed in a layer-by-layer fashion. The intercalated regions consisted of Li-ion channels into which the newly inserted Li ions were pushed atom-by-atom. Interlayer diffusion of Li ions was not observed. Deintercalation was also clearly imaged and was found to transpire in a layer-by-layer mode. The intercalation and deintercalation processes were chemically reversible and can be repeated many times within a few atomic layers. Extensive intercalation of Li ions disrupted the atomically flat surface of MoS2 because of the formation of small lithiated domains that peeled off from the surface of the crystal. The current-potential curves of the intercalation and deintercalation processes were independent of the scan rate, thereby suggesting that the rate-determining step was not governed by Butler-Volmer kinetics.

The electronic structures of eight bathophenanthroline derivatives were elucidated by DFT calculations, and four representatives of which CZBP, m-CZBP, m-TPAP, and BPABP were synthesized and employed as the hosts to afford highly efficient phosphorescent OLEDs. The calculated molecular orbital energies agree well with the experimental results, which further demonstrates that the localization of HOMO and LUMO at the respective hole- and electron-transporting moieties is desirable in bipolar molecular designs.

The polymer poly(4{2-[N,N-bis(trimethylsilyl)amino]ethyl}styrene), prepared by anionic polymerization and of low polydispersity (M(w)/M(n) = 1.10-1.18), has been derivatized by amide linkage to [Ru(II)(bpy)(2)(4-(CO-)-4'-CH(3)-bpy)-](2+) (bpy is 2,2'-bipyridine; 4-(CO-)-4'-CH(3)-bpy is 4-carbonyl-4'-methyl-2,2'-bipyridine). Unreacted amine sites were converted into acetamides by treatment with acetic anhydride to give derivatized polymers of general formula [PS-CH(2)CH(2)NHCO(Ru(II)(n)()Me(m)())](PF(6))(2)(n)(), where m + n = 11, 18, or 25, PS represents the polystyrene backbone, and Ru(II) and Me represent the attached complex and acetamide, respectively. Spectral and electrochemical properties of the derivatized polymers are similar to those of the model [Ru(bpy)(2)(4-CONHCH(2)CH(2)C(6)H(5)-4'-CH(3)-bpy)](2+) (4-CONHCH(2)CH(2)C(6)H(5)-4'-CH(3)-bpy is 4'-methyl-2,2'-bipyridinyl-4-(2-phenylethylamide)), but emission quantum yields (phi(em)) and time-resolved emission decays are slightly dependent on the level of Ru(II) loading, with nonexponential, irradiation-dependent decays appearing at high loadings. The decays could be fitted satisfactorily to the first derivative of the Williams-Watts distribution function. These results are discussed with reference to possible structural and multichromophoric effects on excited-state decay.