Light-emitting electrochemical cells based on mechanochromic, thermally activated delayed fluorescence fish-shaped structures consisting of carbazole derivatives as emitters in the active layer

Abstract

This study surveys the design and synthesis of fish-shaped structures based on carbazole derivatives for applications in light-emitting electrochemical cells (LEECs). Two thermally activated delayed fluorescent dyes (TADF) 5-(3,6-di-tert-butyl-9H-carbazol-9-yl)-10-((3-methoxy-9H-carbazol-9-yl) phenyl) anthracene (dye 1) and 5-(phenoxazine)-10-((3-methoxy-9H-carbazol-9-yl) phenyl) anthracene (dye 2) were synthesized as emitters in the active layer by coupling reaction technique. Separation of the HOMO-LUMO distributions was observed when the HOMOs localized on the methoxycarbazole and phenoxazine derivatives, respectively, and the LUMO consistently localized on the anthracene derivative. The dye consisting of a tert-butyl carbazole derivative showed a lower the variation of singlet-triplet splitting (ΔE_ST) value of 0.04 eV than the other counterpart, and reverse intersystem crossing (RISC) dominated for both dyes. The crystalline dyes exhibited mechanochromic behavior when the photoluminescence (PL) spectrum of the mechanically stimulated dyes was red-shifted. The space charge limited current (SCLC) technique proved that the dye consisting of a phenoxazine derivative had a higher carrier mobility of 6.14 × 10⁻⁴ for holes and 2.12 × 10⁻⁴ cm² V⁻¹ s⁻¹ for electrons in tandem. Based on the mechanochromic behavior of the dyes initially, the fabricated LEECs also exhibited mechanochromic feature, and the EL spectra of the flexible devices showed a red shift in the emission spectra after stretching. In addition, the external quantum efficiency (EQE) of both flexible devices increased to 0.33 % after stretching. Furthermore, iridium complex [Ir(buoppy)₂(dmapzpy)]PF₆ is used as a promising host for the development of high-performance LEECs. Therefore, brightness and EQE values were increased to 6629 cd m⁻² and 7.13 %, respectively.