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

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

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

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

Generation of Blue Light-Emitting Zinc Complexes by Band-Gap Control of the Oxazolylphenolate Ligand System: Syntheses, Characterizations, and Organic Light Emitting Device Applications of 4-Coordinated Bis(2-oxazolylphenolate) Zinc(II) Complexes

Color-tunable Zn(II) complexes of the type Zn(N,O-OPhOxZArX)2 (5), where the ligand consists of an oxazolylphenolate ion connected at the 4-position by a 2,4-substituted aryl functional group with X = NMe2 a, OMe b, Ph c, Cl d, F2 e, and CN f, were prepared. X-ray structural studies of 5a, 5b, and 5e showed that a zinc atom was positioned in a distorted tetrahedral coordination environment created by two oxazolylphenolate ligands with N,O-chelation. Hammet plots of absorption and emission maxima, respectively, in UV and photoluminescence (PL) spectra with respect to electron-donating and electron-withdrawing groups of the substituents indicate a direct correlation between the highest occupied molecular orbital (HOMO)−lowest unoccupied molecular orbital (LUMO) band gaps and electronic alterations at the ligand sites. A similar correlation was also observed for the reduction and oxidation potentials in cyclic voltammograms (CVs). A gradual increase in the HOMO−LUMO band gap is seen from electron-donating to electron-withdrawing functional groups, NMe2 2 5c) was shown to be a potential blue-emitting material, exhibiting a maximum efficiency of 1720 cd/m2 at 17 V with 0.3 cd/A in a multilayered device structure of ITO/NPB/5c/BCP/Alq3/LiF/Al. On the basis of the low HOMO level of this series, 5a was tested as a hole-transporting material; this resulted in the successful fabrication of a multilayered device of ITO/5a/DPVBI/Alq3/LiF/Al with an efficiency of 7000 cd/m2 at 13 V with 2.0 cd/A

Generation of Blue Light-Emitting Zinc Complexes by Band-Gap Control of the Oxazolylphenolate Ligand System: Syntheses, Characterizations, and Organic Light Emitting Device Applications of 4-Coordinated Bis(2-oxazolylphenolate) Zinc(II) Complexes

Color-tunable Zn(II) complexes of the type Zn(N,O-OPhOxZArX)2 (5), where the ligand consists of an oxazolylphenolate ion connected at the 4-position by a 2,4-substituted aryl functional group with X = NMe2 a, OMe b, Ph c, Cl d, F2 e, and CN f, were prepared. X-ray structural studies of 5a, 5b, and 5e showed that a zinc atom was positioned in a distorted tetrahedral coordination environment created by two oxazolylphenolate ligands with N,O-chelation. Hammet plots of absorption and emission maxima, respectively, in UV and photoluminescence (PL) spectra with respect to electron-donating and electron-withdrawing groups of the substituents indicate a direct correlation between the highest occupied molecular orbital (HOMO)−lowest unoccupied molecular orbital (LUMO) band gaps and electronic alterations at the ligand sites. A similar correlation was also observed for the reduction and oxidation potentials in cyclic voltammograms (CVs). A gradual increase in the HOMO−LUMO band gap is seen from electron-donating to electron-withdrawing functional groups, NMe2 2 5c) was shown to be a potential blue-emitting material, exhibiting a maximum efficiency of 1720 cd/m2 at 17 V with 0.3 cd/A in a multilayered device structure of ITO/NPB/5c/BCP/Alq3/LiF/Al. On the basis of the low HOMO level of this series, 5a was tested as a hole-transporting material; this resulted in the successful fabrication of a multilayered device of ITO/5a/DPVBI/Alq3/LiF/Al with an efficiency of 7000 cd/m2 at 13 V with 2.0 cd/A

Generation of Blue Light-Emitting Zinc Complexes by Band-Gap Control of the Oxazolylphenolate Ligand System: Syntheses, Characterizations, and Organic Light Emitting Device Applications of 4-Coordinated Bis(2-oxazolylphenolate) Zinc(II) Complexes

Color-tunable Zn(II) complexes of the type Zn(N,O-OPhOxZArX)2 (5), where the ligand consists of an oxazolylphenolate ion connected at the 4-position by a 2,4-substituted aryl functional group with X = NMe2 a, OMe b, Ph c, Cl d, F2 e, and CN f, were prepared. X-ray structural studies of 5a, 5b, and 5e showed that a zinc atom was positioned in a distorted tetrahedral coordination environment created by two oxazolylphenolate ligands with N,O-chelation. Hammet plots of absorption and emission maxima, respectively, in UV and photoluminescence (PL) spectra with respect to electron-donating and electron-withdrawing groups of the substituents indicate a direct correlation between the highest occupied molecular orbital (HOMO)−lowest unoccupied molecular orbital (LUMO) band gaps and electronic alterations at the ligand sites. A similar correlation was also observed for the reduction and oxidation potentials in cyclic voltammograms (CVs). A gradual increase in the HOMO−LUMO band gap is seen from electron-donating to electron-withdrawing functional groups, NMe2 2 5c) was shown to be a potential blue-emitting material, exhibiting a maximum efficiency of 1720 cd/m2 at 17 V with 0.3 cd/A in a multilayered device structure of ITO/NPB/5c/BCP/Alq3/LiF/Al. On the basis of the low HOMO level of this series, 5a was tested as a hole-transporting material; this resulted in the successful fabrication of a multilayered device of ITO/5a/DPVBI/Alq3/LiF/Al with an efficiency of 7000 cd/m2 at 13 V with 2.0 cd/A

Generation of Blue Light-Emitting Zinc Complexes by Band-Gap Control of the Oxazolylphenolate Ligand System: Syntheses, Characterizations, and Organic Light Emitting Device Applications of 4-Coordinated Bis(2-oxazolylphenolate) Zinc(II) Complexes

Color-tunable Zn(II) complexes of the type Zn(N,O-OPhOxZArX)2 (5), where the ligand consists of an oxazolylphenolate ion connected at the 4-position by a 2,4-substituted aryl functional group with X = NMe2 a, OMe b, Ph c, Cl d, F2 e, and CN f, were prepared. X-ray structural studies of 5a, 5b, and 5e showed that a zinc atom was positioned in a distorted tetrahedral coordination environment created by two oxazolylphenolate ligands with N,O-chelation. Hammet plots of absorption and emission maxima, respectively, in UV and photoluminescence (PL) spectra with respect to electron-donating and electron-withdrawing groups of the substituents indicate a direct correlation between the highest occupied molecular orbital (HOMO)−lowest unoccupied molecular orbital (LUMO) band gaps and electronic alterations at the ligand sites. A similar correlation was also observed for the reduction and oxidation potentials in cyclic voltammograms (CVs). A gradual increase in the HOMO−LUMO band gap is seen from electron-donating to electron-withdrawing functional groups, NMe2 2 5c) was shown to be a potential blue-emitting material, exhibiting a maximum efficiency of 1720 cd/m2 at 17 V with 0.3 cd/A in a multilayered device structure of ITO/NPB/5c/BCP/Alq3/LiF/Al. On the basis of the low HOMO level of this series, 5a was tested as a hole-transporting material; this resulted in the successful fabrication of a multilayered device of ITO/5a/DPVBI/Alq3/LiF/Al with an efficiency of 7000 cd/m2 at 13 V with 2.0 cd/A