Potential Electroluminescent Materials Research Articles

Iridium (III) complexes as promising emitters for solid-state Light-Emitting Electrochemical Cells (LECs)

Light–emitting Electrochemical Cells (LECs) constitute one of the most recent generations of Organic Light–Emitting Diodes (OLEDs). The main difference between LECs and OLEDs is that LECs include mobile ions in the active layer. Ionic transition–metal complexes and especially ionic iridium (III) complexes have recently attracted widespread attention as potential electroluminescent materials for LECs. Herein, we present an overview of LECs incorporating ionic iridium (III) complexes as phosphorescent emitters. Synthetic strategies developed to introduce iridium (III) complexes in the active layer are also reviewed. Despite the numerous intrinsic drawbacks still remaining, recent advances make iridium–based LECs promising devices for future commercial and scientific applications.

Theoretical studies on structures and spectroscopic properties of 10-hydroxybenzo[h]quinoline zinc(II) and its derivatives substituted by cyano-groups

The geometric structures of 10-hydroxybenzo[h]quinoline zinc [Zn(BQ) 2] complex and its derivatives substituted by cyano-groups in the ground state and the lowest singlet excited state were optimized by B3LYP and ab initio CIS methods at LanL2DZ level, respectively. The absorption and emission spectra of these complexes were investigated by the time-dependent density functional theory (TD-DFT) level with PCM model on the basis of the optimized ground and excited states geometries, respectively. The calculated lowest-lying absorptions of all complexes were attributed to ILCT transitions mainly. The calculated emissions of complexes can be described as originated from an excited state with ILCT character mainly. The calculated results showed that the absorption and emission maximums could be tuned by changing the site of the substitutions. The Zn(BQ) 2 and its derivatives substituted by cyano-groups were potential electroluminescent materials with blue, green and yellow light emission.

Synthesis and Characterization of Potential Efficient Electroluminescent Materials: 2-Phenyl-5-[4-(4-phenylamino-2H-1,2,3-triazol-2-yl)]phenyl-1,3,4-oxadiazole Derivatives

Abstract Recently, 1,3,4-oxadiazole-based on heterocyclic compounds were investigated as electroluminescent materials. In this work, we first introduce 1,2,3-triazole to synthesize a series of 1,3,4-oxadiazole–1,2,3-triazole hybrids derivatives as potential electroluminescent materials and explore the effect of modification of the 1,2,3-triazole moiety. The λmax values of the UV–vis of 1,3,4-oxadiazole–1,2,3-triazole hybrids are promoted to longer wavelengths (340–350 nm) than the traditional 1,2,3-triazole derivatives (280–330 nm) in solutions and have a bathochromic shift to 350–360 nm in THF solution. The λmax values of the photoluminescence (PL) spectra are in the range 406–480 nm in solutions. Compound 7h evaporated to form films on quartz substrates, had a maximum at 455 nm and showed a red-shift (≈40 nm) with respect to the solution spectrum. The solution fluorescence quantum yields (Φf) were measured, all of which fell into the range 0.65–0.76, and were determined relative to that of 2-phenyl-5-(4-biphenyl)-1,3,4-oxadiazole in benzene (Φf = 0.80). 1,3,4-Oxadiazole–1,2,3-triazole hybrids derivatives show unclearly reversible reduction processes in cyclic voltammogram measurements. Following spectroscopic studies and observation of the electrochemical behaviors, 1,3,4-oxadiazole–1,2,3-triazole derivatives were determined to be highly potential efficient blue electroluminescent materials.

Naphthalimide incorporating oxadiazole: potential electroluminescent materials with high electron affinity

A new type of naphthalimide derivatives (NI-OXZ) containing oxadiazole moiety has been synthesized and successfully developed as organic electro-transporting electroluminescent (EL) materials. The high electron affinity of oxadiazole moiety in the dyad molecules can increase the electron-injection properties and keep the carrier balance.

Fluorescence spectroscopy of potential electroluminescent materials: Substituent effects on DSB and segmented PPV derivatives

The absorption and fluorescence of substituted distyrylbenzene (DSB) derivatives and segmented poly(phenylene vinylene) (PPV) derivatives are characterized by long-wavelength absorption maxima and absorption coefficients of λa = 380–450 nm, e = 20,000–60,000 M−1 cm1 and fluorescence maxima, quantum yields, and decay times of λr = 440–530 nm, Φf = 0.2–0.9, and Τ = 0.8–2.5 ns, respectively. Alkoxy substituents at the central phenylene ring of DSB groups increase the bathochromic shift in the spectra in comparison to DSB, without a significant decrease in the high DSB fluorescence quantum yield. Both phenyl and cyano substitutions at the vinylene bridge lead to a further bathochromic shift of the fluorescence and a decrease in the quantum yield to ca. 0.4. The DSB derivatives and the related segmented PPV derivatives show nearly the same absorption spectra, fluorescence spectra, and radiative rate constantsk f= Φf/Τ, indicating the efficacy of the segmentation of the polymer chain. The radiative rate constants determined by the Φf and Τ values and by the Strickler/Berg formula are in reasonable agreement. This supports the possibility of interpreting the properties of the polymers in terms of their DSB units. The decrease in the emission anisotropy can be ascribed to multistep energy transfer processes between different oriented segments.