Diphenylamino- or cabazolyl-endcapped silafluorene derivatives which show a wide energy band gap, a high fluorescence quantum yield and high stability have been designed, synthesized, and characterized. Double layer electroluminescent devices of these silafluorene derivatives exhibited efficient blue emission. The non-doped double layer OLEDs containing TDMS, TDPS, CDMS, or CDPS exhibited better electroluminescence efficiencies than those of the devices using the reference emitter DPFL-NPB, among which the best device was with TDPS, which showed a maximum current efficiency of 1.62 cd A−1 and an external quantum efficiency (EQE) of 1.36%. The solution processed device using TDPS as dopant exhibited a high performance with an EQE of 2.48% and an obviously low turn-on voltage of 4 V, when compared to the results of the reference device. The replacement of the carbon atom of the fluorene unit with a silicon atom could lower the energy gap effectively and improve the thermal stability as well as optical performances. The results indicate that the end-capped arylamino groups affect the organic light-emitting diode (OLED) performances greatly and aryl or alkyl substitution on the 9-position of a silafluorene unit is also crucial to the OLED performances of this kind of silafluorene.

A series of fluorene derivatives end-capped with diphenylamino and oxadiazolyl were synthesized, and their photophysical and electrochemical properties are reported. Aggregation-induced emission (AIE) effects were observed for the materials, and bipolar characteristics of the molecules are favored with measurement of carrier mobility and calculation of molecular orbitals using density functional theory (DFT). Using the fluorene derivatives as emitting-layer, nondoped organic light-emitting devices (OLEDs) have been fabricated by spin-coating in the configuration ITO/PEDOT:PSS(35 nm)/PVK(15 nm)/PhN-OF(n)-Oxa(80 nm)/SPPO13(30 nm)/Ca(8 nm)/Al(100 nm) (n = 2–4). The best device with PhN-OF(2)-Oxa exhibits a maximum luminance of 14 747 cd/m2, a maximum current efficiency of 4.61 cd/A, and an external quantum efficiency (EQE) of 3.09% in the blue region. Investigation of the correlation between structures and properties indicates that there is no intramolecular charge transfer (ICT) increase in these molecules with the increase of conjugation length. The device using material of the shortest conjugation length as emitting-layer gives the best electroluminescent (EL) performances in this series of oligofluorenes.Keywords: AIE-active; blue; fluorene; nondoped; organic light-emitting devices

•New fluorene derivatives were synthesized for non-doped single-layer OLEDs.•One of derivatives exhibits deep-blue emission in device.•Derivative with thienyl unit shows best OLED device performance.•Emission color is tunable by changing the conjugation core and/or length.Diphenylamino- and triazole-endcapped fluorene derivatives which show a wide energy band gap, a high fluorescence quantum yield and high stability have been synthesized and characterized. Single-layer electroluminescent devices of these fluorene derivatives exhibited efficient deep blue to greenish blue emission at low driving voltage. The single-layer OLED of PhN-OF(1)-TAZ shows a maximum current efficiency of 1.54 cd/A at 20 mA cm−2 with external quantum efficiency (EQE) of 2.0% and CIE coordinates of (0.153, 0.088) in deep blue region, while the single-layer device of oligothienylfluorene PhN-OFOT-TAZ shows a maximum brightness of 7524 cd/m2 and a maximum current efficiency of 2.9 cd/A with CIE coordinates of (0.20, 0.40) in greenish blue.Graphical abstract

A series of donor–acceptor systems incorporating a carbazole moiety as the donating unit and pyridine moiety as the accepting unit have been designed and synthesized. The spectroscopic and electrochemical behaviors of the carbazole derivatives demonstrate that the carbazole unit interacts with the electron-accepting group through the π-conjugated spacer, thus leading to the intramolecular charge transfer (ICT). The pyridine-substituted carbazole derivatives show significant sensing and coordinating properties toward a wide range of metal cations. Compound S2 exhibits fluorescence enhancement upon association with transition metal cations, and compound V3 shows high selectivity for Cu2+ among this series of materials. DFT calculations indicate the different association abilities of the dyes and the enhancement of ICT upon addition of the metal cations.

Diphenylamino- or cabazolyl-endcapped silafluorene derivatives which show a wide energy band gap, a high fluorescence quantum yield and high stability have been designed, synthesized, and characterized. Double layer electroluminescent devices of these silafluorene derivatives exhibited efficient blue emission. The non-doped double layer OLEDs containing TDMS, TDPS, CDMS, or CDPS exhibited better electroluminescence efficiencies than those of the devices using the reference emitter DPFL-NPB, among which the best device was with TDPS, which showed a maximum current efficiency of 1.62 cd A−1 and an external quantum efficiency (EQE) of 1.36%. The solution processed device using TDPS as dopant exhibited a high performance with an EQE of 2.48% and an obviously low turn-on voltage of 4 V, when compared to the results of the reference device. The replacement of the carbon atom of the fluorene unit with a silicon atom could lower the energy gap effectively and improve the thermal stability as well as optical performances. The results indicate that the end-capped arylamino groups affect the organic light-emitting diode (OLED) performances greatly and aryl or alkyl substitution on the 9-position of a silafluorene unit is also crucial to the OLED performances of this kind of silafluorene.