Electrochemically Active Dendrimers for the Manufacture of Multilayer Films: Electrochemical Deposition or Polymerization Process by End-Capped Triarylamine or Carbazole Dendrimer

Two different end-capped triarylamine and carbazole dendrimers of the types Gn-2n+1NPB and Gn-2n+1CBP (n = 1, 2, 3, 4) were prepared by divergent synthesis by reacting diethenyl propagating carbosilane dendrimers with suitable functional groups, such as naphthylphenylaminophenyl (NPB) and carbazolylphenyl (CBP) units. The electrochemical studies of these two series showed that the electrochemical properties of each dendrimer in both solution and on the immobilized electrode were dependent on the generation of dendrites and type of periphery group. Gn-2n+1NPB dendrimers (n = 3, 4) underwent oxidative precipitation on the electrode surface without a proceeding electrochemical reaction only to form highly charged ammonium cations, whereas the Gn-2n+1CBP dendrimers produced cross-linked polymers via an oxidative polymerization process. The ammonium cationic species of the G3-16NPB dendron was confirmed on the basis of the characteristic 1s peak of the F atom in X-ray photoelectron spectroscopy (XPS). Overall, the electrochemically activated G3-16NPB dendron transforms to a highly charged species with peripheral NR3+BF4− units to undergo an electrodeposition (ED) process. As a result, the NPB and CBP dendrimers produce dissimilar deposited films, exhibiting different surface morphology and hydrophilicity based on atomic force microscope and contact angle measurements. Using these two dissimilar electrochemical deposition processes, a new method for fabricating multilayer thin films on a conducting substrate was demonstrated successfully

Emission Enhancement of Anthracene Derivative Caused by a Dramatic Molecular Orbital Change on the Nanosheet Surface

The emission enhancement phenomenon on clay nanosheets is called surface-fixation-induced emission (S-FIE) and is similar to aggregation-induced emission, which has attracted the attention of many researchers. Both emission enhancement phenomena are primarily caused by the suppression of nonradiative deactivation. In this study, a new S-FIE molecule was synthesized and its basic photochemical behavior was investigated. The emission enhancement of the new molecule on the clay surface was induced by the suppression of nonradiative deactivation and acceleration of radiative deactivation. Density functional theory calculations indicated that the acceleration of radiative deactivation originated from the improvement in the spatial overlap between the two molecular orbitals related to the emission phenomenon and the increase in the Frank–Condon factor

Spiro-silacycloalkyl Tetraphenylsiloles with a Tunable Exocyclic Ring: Preparation, Characterization, and Device Application of 1,1‘-Silacycloalkyl-2,3,4,5-tetraphenylsiloles

A series of 2,3,4,5-tetraphenylsiloles (3), with a four- to six-membered silacyclo alkyl substituent at the 1,1‘-position, have been prepared by a one-pot synthesis of dilithium diyne (2) with the corresponding silacycloalkyl dichlorosilane precursors (1). The structures of the resulting 1,1‘-(silacyclopentenyl)silole (3b) and 1,1‘-(silacyclopentyl)silole (3c) species were studied using X-ray crystallography to obtain geometrical information on exocyclic siloles. Due to the formation of silacyclopentenyl and -pentyl rings, the phenyl substituents on the silole adopted a paddle-wheel conformation to reduce steric hindrance between substituents. The photophysical properties of the silacycloalkyl siloles (3) were examined to elucidate the structure−photophysical property relationship arising from variation of the exocyclic ring size. Indeed, the size of the exocyclic silacycloalkyl ring at the 1,1‘-position affected the maximum peaks in the absorption and emission spectra, with systematic blue shifts being observed with increasing exocyclic ring size. A sequential elevation of the LUMO levels was monitored by observing increases in the reduction potential, as seen in the cyclic voltammograms (CVs), with increasing exocyclic ring size. In addition, due to the formation of exocyclic rings, an enhanced thermal stability was observed on the basis of DSC measurements, showing that silacyclopentylsilole (3c) exhibits the highest Tg value in the series. Indeed, a three-layer device comprising N,N‘-bis(1-naphthyl)-N,N‘-diphenylbenzidine (NPB) as the hole-transport layer, 3c as the emitting layer, and Alq3 as the electron-transport layer displayed a brightness of 11 000 cd/m2 at 11 V with a current efficiency of 2.71 cd/A

Emission Color Tuning and Deep Blue Dopant Materials Based on 1,6-Bis(<i>N</i>-phenyl-<i>p</i>-(<i>R</i>)-phenylamino)pyrene

Panchromatic 1,6-bis(N-phenyl-p-(R)-phenylamino)pyrenes, 2R, were obtained from Buchwald−Hartwig coupling reactions between N-phenyl-p-(R)-phenylamines and 1,6-dibromopyrene. The photophysical properties of 2R corresponded well to the electron-withdrawing and -donating nature of the diarylamine substituents, exhibiting a full color visible range between 454 and 620 nm. In particular, a deep blue 2CN showed a high radiative rate constant of 2.85 × 108 s−1 with high emission quantum efficiency of 79%. Further applications of 2CN as a blue dopant were attempted using multilayer organic light-emitting devices. A maximum efficiency of 3.98 cd/A with CIE coordinates of x = 0.14, y = 0.10 were obtained

Efficient Light Harvesting and Energy Transfer in a Red Phosphorescent Iridium Dendrimer

A series of red phosphorescent iridium dendrimers of the type [Ir­(btp)₂(pic-PC_<i>n</i>)] (<b>Ir-G</b>_{<b><i>n</i></b>}; <i>n</i> = 0, 1, 2, and 3) with two 2-(benzo­[<i>b</i>]­thiophen-2-yl)­pyridines (btp) and 3-hydroxypicolinate (pic) as the cyclometalating and ancillary ligands were prepared in good yields. Dendritic generation was grown at the 3 position of the pic ligand with 4-(9<i>H</i>-carbazolyl)­phenyl dendrons connected to 3,5-bis­(methyleneoxy)­benzyloxy branches (PC_<i>n</i>; <i>n</i> = 0, 2, 4, and 8). The harvesting photons on the PC_<i>n</i> dendrons followed by efficient energy transfer to the iridium center resulted in high red emissions at ∼600 nm by metal-to-ligand charge transfer. The intensity of the phosphorescence gradually increased with increasing dendrimer generation. Steady-state and time-resolved spectroscopy were used to investigate the energy-transfer mechanism. On the basis of the fluorescence quenching rate constants of the PC_<i>n</i> dendrons, the energy-transfer efficiencies for <b>Ir-G</b>_<b>1</b>, <b>Ir-G</b>_<b>2</b>, and <b>Ir-G</b>_<b>3</b> were 99, 98, and 96%, respectively. The energy-transfer efficiency for higher-generation dendrimers decreased slightly because of the longer distance between the PC dendrons and the core iridium­(III) complex, indicating that energy transfer in <b>Ir-G</b>_{<b><i>n</i></b>} is a Förster-type energy transfer. Finally, the light-harvesting efficiencies for <b>Ir-G</b>_<b>1</b>, <b>Ir-G</b>_<b>2</b>, and <b>Ir-G</b>_<b>3</b> were determined to be 162, 223, and 334%, respectively

End-Capped Silole Dendrimers on a Carbosilane Periphery: Potential Electroluminescent Materials^⊥

The divergent synthesis of end-capped silole dendrimers Gn-2n+1Silole (n = 1−4) using 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane [Me(CH2CH)SiO]4 as a core molecule and allyl alcohol/dichloromethylsilane as a building block is described in this paper. The reaction of the dichloride functionalities of the carbosiloxane dendrimers Gn-2n+2Cl (n = 1−4) with the 1,4-diphenylbutadiene-1,4-dianions (1) provided an effective route for the attachment of silole functionalities to a dendritic periphery. In addition, dendritic siloles GBn-2nSilole (n = 1−3) based on phenylethynylmethylsilane (PhC⋮C)2Me2Si as cores were synthesized. The building blocks of the dendrimers consisted of double bonds (−PhCCHMeSi−) in the inner shell and silole groups on the outermost periphery. The generational limit of the dendrimer for the two-branching type core molecule was found to have eight silole groups for the third generation. All of the dendrimers were characterized by 1H and 13C{1H} NMR, UV spectroscopy, cyclic votammetry (CV), and size exclusion chromatography (SEC). Using this methodology, a series of silole-containing dendrimer systems showing green to greenish-blue fluorescence were synthesized

Spiro-silacycloalkyl Tetraphenylsiloles with a Tunable Exocyclic Ring: Preparation, Characterization, and Device Application of 1,1‘-Silacycloalkyl-2,3,4,5-tetraphenylsiloles

A series of 2,3,4,5-tetraphenylsiloles (3), with a four- to six-membered silacyclo alkyl substituent at the 1,1‘-position, have been prepared by a one-pot synthesis of dilithium diyne (2) with the corresponding silacycloalkyl dichlorosilane precursors (1). The structures of the resulting 1,1‘-(silacyclopentenyl)silole (3b) and 1,1‘-(silacyclopentyl)silole (3c) species were studied using X-ray crystallography to obtain geometrical information on exocyclic siloles. Due to the formation of silacyclopentenyl and -pentyl rings, the phenyl substituents on the silole adopted a paddle-wheel conformation to reduce steric hindrance between substituents. The photophysical properties of the silacycloalkyl siloles (3) were examined to elucidate the structure−photophysical property relationship arising from variation of the exocyclic ring size. Indeed, the size of the exocyclic silacycloalkyl ring at the 1,1‘-position affected the maximum peaks in the absorption and emission spectra, with systematic blue shifts being observed with increasing exocyclic ring size. A sequential elevation of the LUMO levels was monitored by observing increases in the reduction potential, as seen in the cyclic voltammograms (CVs), with increasing exocyclic ring size. In addition, due to the formation of exocyclic rings, an enhanced thermal stability was observed on the basis of DSC measurements, showing that silacyclopentylsilole (3c) exhibits the highest Tg value in the series. Indeed, a three-layer device comprising N,N‘-bis(1-naphthyl)-N,N‘-diphenylbenzidine (NPB) as the hole-transport layer, 3c as the emitting layer, and Alq3 as the electron-transport layer displayed a brightness of 11 000 cd/m2 at 11 V with a current efficiency of 2.71 cd/A

Enhanced Charge-Carrier Mobility Derived from Cyclization of a Silanylene Unit on Dithienosiloles: Syntheses, Photophysical Properties, and Device Fabrication of Dithieno-spiro-siloles

A series of trimethylsilyl-substituted dithieno-spiro-siloles (3), with a four- to six-membered silacycloalkyl substituent at the 1,1-position, were prepared by reacting 3,3′-dilithio-5,5′-bis(trimethylsilyl)-2,2′-dithiophene (2) with the corresponding silacycloalkyl dichlorosilane precursors (1). Arylamino-substituted bis(diarylamino)dithieno-spiro-siloles (6) were also prepared using the same synthetic protocol by reacting 3,3′-dilithio-5,5′-bis(diarylamino)-2,2′-dithiophene (5) with 1. A structural study of the five-membered dithieno-spiro-silole, 1,1-(silacyclopentenyl)dithieno-spiro-silole (3b), was undertaken and showed a reduced intermolecular distance in the solid state. This resulted in enhanced charge-carrier mobility, which was confirmed by a time-of-flight (TOF) measurement of 6b. The electronic properties of dithienosiloles (6) were studied for device fabrication by applying them as emitting materials in multilayer devices. Thus, I−V characteristics of multilayer devices, comprising N,N′-bis(1-naphthyl)-N,N′-diphenylbenzidine (NPB) as the hole-transport layer, 6 as the emitting layer, 2,9-dimethyl-4,7-diphenylphenanthroline (BCP) as the hole-blocking layer, and tris(8-quinolinato)aluminum (Alq3) as the electron-transporting layer, showed that the dithieno-spiro-siloles (6b−d) exhibited turn-on voltages (2.2−2.8 V) lower than those of optimized dithienosilole (2Ph-NPB) (4.3 V). Furthermore, systematic blue shifts in both UV and PL spectra were observed in the bis(trimethylsilyl)dithieno-spiro-silole series (3) as the size of the exocyclic silanylene ring was increased, whereas bis(diarylamino)dithieno-spiro-siloles (6) exhibited only a small variation along the series due to extensive conjugation from the peripheral diarylamine to the dithienosilole core. This blue shift is attributed to elevation of the LUMO level on the basis of a DFT calculation on 3, along with UV spectral data and cyclic voltammograms

Enhanced Charge-Carrier Mobility Derived from Cyclization of a Silanylene Unit on Dithienosiloles: Syntheses, Photophysical Properties, and Device Fabrication of Dithieno-spiro-siloles

A series of trimethylsilyl-substituted dithieno-spiro-siloles (3), with a four- to six-membered silacycloalkyl substituent at the 1,1-position, were prepared by reacting 3,3′-dilithio-5,5′-bis(trimethylsilyl)-2,2′-dithiophene (2) with the corresponding silacycloalkyl dichlorosilane precursors (1). Arylamino-substituted bis(diarylamino)dithieno-spiro-siloles (6) were also prepared using the same synthetic protocol by reacting 3,3′-dilithio-5,5′-bis(diarylamino)-2,2′-dithiophene (5) with 1. A structural study of the five-membered dithieno-spiro-silole, 1,1-(silacyclopentenyl)dithieno-spiro-silole (3b), was undertaken and showed a reduced intermolecular distance in the solid state. This resulted in enhanced charge-carrier mobility, which was confirmed by a time-of-flight (TOF) measurement of 6b. The electronic properties of dithienosiloles (6) were studied for device fabrication by applying them as emitting materials in multilayer devices. Thus, I−V characteristics of multilayer devices, comprising N,N′-bis(1-naphthyl)-N,N′-diphenylbenzidine (NPB) as the hole-transport layer, 6 as the emitting layer, 2,9-dimethyl-4,7-diphenylphenanthroline (BCP) as the hole-blocking layer, and tris(8-quinolinato)aluminum (Alq3) as the electron-transporting layer, showed that the dithieno-spiro-siloles (6b−d) exhibited turn-on voltages (2.2−2.8 V) lower than those of optimized dithienosilole (2Ph-NPB) (4.3 V). Furthermore, systematic blue shifts in both UV and PL spectra were observed in the bis(trimethylsilyl)dithieno-spiro-silole series (3) as the size of the exocyclic silanylene ring was increased, whereas bis(diarylamino)dithieno-spiro-siloles (6) exhibited only a small variation along the series due to extensive conjugation from the peripheral diarylamine to the dithienosilole core. This blue shift is attributed to elevation of the LUMO level on the basis of a DFT calculation on 3, along with UV spectral data and cyclic voltammograms

<i>o</i>-Phenylene-Bridged Cp/Amido Titanium Complexes for Ethylene/1-Hexene Copolymerizations

o-Phenylene-bridged Me3Cp/amido titanium complexes have been prepared via the Suzuki coupling reaction. Some of them show reactivity comparable to that of the CGC [Me2Si(η5-Me4Cp)(NtBu)]TiCl2 in ethylene/1-hexene copolymerization in terms of activity, molecular weight, and comonomer incorporation