Rational molecular design of efficient yellow-red dendrimer TADF for solution-processed OLEDs: a combined effect of substitution position and strength of the donors

The development of high-performance solution-processed red organic light-emitting diodes(OLEDs) remains a challenge,particularly in terms of maintaining efficiency at high luminance. Here, we designed and synthesized four novel orange-red thermally activated delayed fluorescence(TADF) dendrimers that are solution-processable: 2GCz BP, 2DPACz BP, 2FBP2GCz and 2FBP2DPACz. We systematically investigated the effect of substitution position and strength of donors on the optoelectronic properties. The reverse intersystem crossing rate constant(kRISC) of the emitters having donors substituted at positions 11and 12 of the dibenzo[a,c]phenazine(BP) is more than 10-times faster than that of compounds substituted having donors substituted at positions 3 and 6. Compound 2DPACz BP, containing stronger donors than 2GCz BP, exhibits a red-shifted emission and smaller singlet-triplet energy splitting, ΔE_(ST), of 0.01 e V. The solution-processed OLED with 10 wt% 2DPACz BP doped in m CP emitted at 640 nm and showed a maximum external quantum efficiency(EQE_(max)) of 7.8%, which was effectively maintained out to a luminance of 1,000 cd m-2. Such a device's performance at relevant display luminance is among the highest for solution-processed red TADF OLEDs. The efficiency of the devices was improved significantly by using 4Cz IPN as an assistant dopant in a hyperfluorescence(HF) configuration, where the 2DPACz BP HF device shows an EQEmaxof 20.0% at λEL of 605 nm and remains high at 11.8% at a luminance of 1,000 cd m-2, which makes this device one of the highest efficiency orange-to-red HF SP-OLEDs to date.

Red organic light-emitting diodes based photobiomodulation therapy enabling prominent hair growth

Hair loss can cause psychological distress.Here,red organic light-emitting diode(OLED)light source is first introduced as the photobiomodulation therapy(PBMT)for hair growth and demonstrated as a promising and non-invasive therapeutic modality for alopecia.OLED exhibits unique advantages of homogeneous irradiation,flexible in form factor,less heat generation.These features enable OLED to be an ideal candidate for wearable PBMT light sources.A systematic study of using red OLEDs to facilitate hair growth was conducted.The results show that OLEDs excellently promote hair regrowth.OLED irradiation can increase the length of the hair by a factor of 1.5 as compared to the control,the hair regrowth area is enlarged by over 3 times after 20 days of treatments.Moreover,the mechanism of OLED that stimulates hair follicle regeneration is investigated invivo by conducting a systematic controlled experiments on mice with or without OLED PBMT.Based on the comprehensive histological and immunofluorescence staining studies,two key factors are identified for red OLEDs to facilitate hair follicle regeneration:(i)increased autophagy during the anagen phase of the hair growth cycle;(ii)increased blood oxygen content promoted by the accelerated microvascular blood flow.