Thioxanthene and dioxothioxanthene dihydroindeno[2,1-b]fluorenes: synthesis, properties and applications in green and sky blue phosphorescent OLEDs

Abstract

We report herein the synthesis, and structural, electrochemical and photophysical properties of new dihydroindeno[2,1-b]fluorene-based semi-conductors, i.e. dispiro[thioxanthene-9,5′-indeno[2,1-b]fluorene-7′,9′′-thioxanthene] 2 and dispiro-[dioxothioxanthene-9,5′-indeno[2,1-b]fluorene-7′,9′′-thioxanthene] 3. These properties will be compared to those of the pure hydrocarbon derivative dispiro[fluorene-9,5′-indeno[2,1-b]fluorene-7′,9′′-fluorene] 1 previously described. The incorporation of the sulfur atom within the bridged units allows tuning the HOMO and LUMO energy levels, nevertheless retaining the high E_T of the dihydroindeno[2,1-b]fluorenyl core ([2,1-b]IF), the key feature of further device applications. This control of the properties has allowed incorporating 3 as the host material in blue and green phosphorescent OLEDs (PhOLEDs) with an EQE of 12.8% (at 1 mA cm⁻² with the corresponding CE and PE of 48.6 cd A⁻¹ and 29.5 lm W⁻¹) for the green device and an EQE of 4.8% (at 1 mA cm⁻² with the corresponding CE and PE of 14.8 cd A⁻¹ and 8.2 lm W⁻¹) for the sky-blue device. To the best of our knowledge, this work is the second example of incorporation of a dihydroindeno[2,1-b]fluorene based semi-conductor in a blue PhOLED and highlights the potential of this fragment in organic electronics.