Taking advantage of the excellent luminescence properties of 2a-c as well as their high thermal stability (325°C < Td(2a-c) < 330°C), compounds 2a-c were inserted as emitters into multilayered OLED devices (see the ESI for details). Because of their suitable HOMO-LUMO levels and their high solid-state luminescence, 2a-c were used as pure emitter and inside a host 4,4-bis(2,2-diphenylvinyl)-1,1-diphenyl (DPVBi) matrix. The performances of the OLED devices are reported in Table for 2a-c used as pure emitters or at a doping ratio of 5% in DPVBi matrix. This doping ratio of 5% have been set after a study of EQE vs doping ratio on 2a (see Fig. ). 2a). The theoretical value of 5% EQE for a fluorescent OLED is even reached with compound 2a in device A. Moreover, device A displays a small roll-off efficiency illustrated by its very high brightness of 27010 cd.m -2 at a high current density of 220 mA.cm -2 . These values represent a considerable increase compared to previously reported related compounds and thus highlight the dramatic impact of small molecular variations on the properties of the device. Devices containing pure emitter in the emissive layer display less efficient properties than devices containing DPVBi (EQE(A) = 5.1%; EQE(D) = 3.6%). Interestingly, Von of devices D, E, and F are significantly lower than in devices A, B, and C (by ca. 1 V), meaning that the injection of charge inside the emissive layer is easier when there is no DPVBi. This property leads to better stability of devices D, E, and F: the maximal brightness is reached at a higher value of current density (300 to 340 mA.cm -2 ) than in devices A, B, and C (140 to 220 mA.cm -2 ). To rationalize the difference of EQE, the photoluminescence of emissive layers (deposited on a glass substrate using evaporation) was studied (Table ). DPVBi has almost no impact on the PLQY of 2a (PL(5% in dPVBi)= 0,93 and PL(pure) = 0,90) while the impact on 2b and 2c is much larger (PL(2b 5% in dPVBi)= 0,85; PL(2b pure) = 0,54; PL(2c 5% in DPVBi)= 0,36; PL(2c pure) = 0,16). This effect is related to the ICT character of the emissive transition of 2a-c: the apolar environment of DPVBI enhances the contribution of the locally-excited state, higher in energy and more emissive than the ICT state. Such behavior explains both hypsochromic shift and the higher EQE for devices A, B and C using a host matrix.