Fluorescence control on panchromatic spectra via c-alkylation on arylated quinoxalines.

A coherent green fluorescence was obtained by butylation at the 2-position of panchromatic 2,3-diaryl-5,8-diarylquinoxalines (2) to give corresponding 2-butyl-2,3-diaryl-5,8-diaryl-1H-quinoxalines (3). Full color quinoxaline derivatives (2) were prepared from electronic modification at either the 2,3- or 5,8-positions at the peripheral ArX group or X group (X = -H, -OMe, -NPh(2), -NMe(2), -NMePh) of the quinoxalines. 2-Butylation converted one imine unit of the pyrazine ring to an amine group, which effectively altered the electron donor and acceptor functions to produce a coherent green fluorescence.

Turning on fluorescent emission from C-alkylation on quinoxaline derivatives.

Reduction on imine moiety (C=N) of quinoxalines by alkyl-/aryllithiums led to a geometrical change on the quinoxaline ring, thereby perturbing the electronic structure to turn on fluorescence emission. Such a structural change resulted in interrupted cyclic-ring systems with electron-donating amine (sp(3)-type) and electron-accepting imine (sp(2)-type) units bridged by a phenylene unit. Through either alkylation or arylation, a highly polarized electron donor-electron acceptor bipolar system was established in a single molecule with dramatically enhanced PL efficiency (up to 60%).

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-OPh (OxZ)ArX) 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 = NMe 2 a, OMe b, Ph c, Cl d, F 2 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, NMe 2 < OMe < Ph < Cl < F 2 < CN. An emission peak with a maximum at 455 nm was achieved when the most electron-withdrawing group (cyano) was applied to the oxazolylphenolate ligand system. Density-functional theory (DFT) calculations on the HOMOs and LUMOs for this series lead to a conclusion similar to that arrived at from a blue-shift trend observed in UV data and trends in the CVs. The 4-coordinated zinc complex ( 5c) was shown to be a potential blue-emitting material, exhibiting a maximum efficiency of 1720 cd/m (2) at 17 V with 0.3 cd/A in a multilayered device structure of ITO/NPB/ 5c/BCP/Alq 3/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/Alq 3/LiF/Al with an efficiency of 7000 cd/m (2) at 13 V with 2.0 cd/A.