Full emission color tuning in bis-dipolar diphenylamino-endcapped oligoarylfluorenes

A novel series of monodisperse bis-dipolar emissive oligoarylfluorenes, OF(2)Ar-NPh, bearing an electron affinitive core, 9,9-dibutylfluorene as conjugated bridges, and diphenylamino as end-caps was successfully synthesized by a convergent approach using palladium catalyzed Suzuki cross-coupling. The results of optical and electrochemical investigations showed that the HOMO, LUMO, and energy gap of these diphenylamino endcapped oligoarylfluorenes can easily be modified or tuned by the use of various electron affinitive central aryl cores that included dibenzothiophene, phenylene, oligothiophenes, 2,1,3-benzothiadiazole, 4,7-dithien-2-yl-2,1,3-benzothiadiazole, thiophene S,S′-dioxide, and dibenzothiophene S,S′-dioxide as well as the extent of the π-conjugated core. As a result, their emission bands measured in chloroform can cover the full UV-vis spectrum (from 412 to 656 nm). In contrast to the common dipolar chromophores, most of OF(2)Ar-NPhs can form morphologically stable amorphous thin films (T_g = 88-127°C) with a high decomposition temperature, T_dec > 450°C. Remarkably, undoped OF(2)Ar-NPh-based multilayer OLEDs could exhibit good to excellent device performance with emission colors spanning the full UV-vis spectrum. OF(2)Ar-NPh bearing oligothiophene core based devices exhibit a maximum luminance of 5000-12500 cd m^-2 and luminous efficiency up to 3.6-4.0 cd A^-1. Our findings provide a practical approach to design and tune the color emission of efficient and potentially useful light emitting materials.