Synthesis and thermal, electrochemical, photophysical properties of novel symmetric/asymmetric indolo[2,3-a]carbazole derivatives bearing different aryl substituents

• Ten new compounds with Indolo[2,3-a]carbazole as backbone was designed and synthesized by Symmetric/Asymmetric modification.
• The symmetric substituted indolo[2,3-a]carbazole derivatives (6a-e) are more suitable for application in blue emitters for OLEDs.
• The introduction of a more electronegative group is good to improve the energy gaps.
• Compounds 6d and 6e are the most potential for application in hole-transport and host materials.

A series of new symmetric/asymmetric aryl-substituted indolo[2,3-a]carbazole derivatives were designed and synthesized. The thermal stability, photophysical properties and electrochemical properties of these compounds were characterized by thermal analysis, UV absorption spectra, photoluminescence (PL) spectrometer, quantum calculation texting and cyclic voltammetric (CV) measurements. Compared with these compounds, symmetric substituted indolo[2,3-a] carbazole derivatives (6a-e) exhibit good properties as Luminescent materials. The compounds (6a-e) showed high thermal stability with thermal decomposition temperatures at 5% weight loss in a range of 312–370 °C. In the solution and the solid states, these compounds exhibited stable blue light emission. The optical band gaps of compounds 6a-e in CH2Cl2 solution were in a range of 3.09–3.32 eV. The wide energy gaps are helpful to electronic transfers and transports. The introduction of a more electronegative –F or -CF3 group at the meta or para-position of the phenyl rings in the compounds 6d and 6e were good for improving the energy gaps. Compared with other compounds, compounds 6d and 6e are more potential for application in blue OLEDs.

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