Synthesis, characterization, and properties of 7,7′-bis(3,6-di-tert-butylcarbazol-N-yl)-substituted fluorenyl-oligothiophenes

A series of new 7,7′bis(3,6-di-tert-butylcarbazol-N-yl)-substituted fluorenyl-oligothiophenes bearing 0-, 2-, 4-, 6-, and 8-thiophene rings, namely BCFTn, were synthesized using palladium catalyzed Stille dimerization coupling reactions of their corresponding brominated thiophenes. The relationship between the chemical structure and the properties of these oligomers was evaluated. With respect to the electronic properties, the longest wavelength absorptions, emissions, and also the oxidation potentials can be tuned by varying the conjugation length of the oligothiophene segments. The terminal carbazole and fluorene moieties of the resulting materials are beneficial for their morphology, conjugation length, and solubility.     

Synthesis and properties of oligofluorene-thiophenes as emissive materials for organic electroluminescent devices: color-tuning from deep blue to orange

A series of oligofluorene-thiophenes end-capped with 3,6-di-tert-butylcarbazole and pyrene were designed and synthesized for application as color tunable emissive materials for organic electroluminescent devices. They were characterized by ¹H NMR, ¹³C NMR, FT-IR, UV–vis, PL spectroscopy, and mass spectrometry. Theoretical calculations revealed that the carbazole moiety attached to the end of the molecule is nearly perpendicular to oligofluorene-thiophene-pyrene plane and π-electrons in the ground state delocalize over the entire molecule. Their optical, thermal, and electrochemical properties could be tuned by varying the number of thiophene units in the molecule. All were electrochemically and thermally stable molecules. OLED devices of these materials emitted brightly in various colors from deep blue to orange. Particularly, deep blue (CIE coordinates of 0.16, 0.14) and green (CIE coordinates of 0.27, 0.61) devices showed high color quality close to the NTSC standards with high luminance efficiencies of 1.14 and 11.15 cd/A, respectively.     

The effect of conjugated spacer on novel carbazole derivatives for dye‐sensitized solar cells: Density functional theory/time‐dependent density functional theory study

The ground‐state structure and frontier molecular orbital of D‐π‐A organic dyes, CFT1A, CFT2A, and CFT1PA were theoretically investigated using density functional theory (DFT) on B3LYP functional with 6‐31G(d,p) basis set. The vertical excitation energies and absorption spectra were obtained using time‐dependent DFT (TD‐DFT). The adsorptions of these dyes on TiO₂ anatase (101) were carried out by using a 38[TiO₂] cluster model using Perdew–Burke–Ernzerhof functional with the double numerical basis set with polarization (DNP). The results showed that the introduction of thiophene–thiophene unit (T–T) as conjugated spacer in CFT2A could affect the performance of intramolecular charge transfer significantly due to the inter‐ring torsion of T–T being decreased compared with phenylene–phenylene (P–P) spacer of CFP2A in the researhcers' previous report. It was also found that increasing the number of π‐conjugated unit gradually enhanced charge separation between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of these dyes, leading to a high‐efficiency photocurrent generation. The HOMO–LUMO energy gaps were calculated to be 2.51, 2.37, and 2.50 eV for CFT1A, CFT2A, and CFT1PA respectively. Moreover, the calculated adsorption energies of these dyes on TiO₂ cluster were ～14 kcal/mol, implying that these dyes strongly bind to TiO₂ surface. Furthermore, the electronic HOMO and LUMO shapes of all dye–TiO₂ complexes exhibited injection mechanism of electron via intermolecular charge‐transfer transition. © 2012 Wiley Periodicals, Inc.