Tetraphenylethylene-BODIPY aggregation-induced emission luminogens for near-infrared polymer light-emitting diodes

The aggregation-induced emission(AIE) phenomenon provides a new direction for the development of organic light-emitting devices. Here, we present a new class of emitters based on 4,4-difluoro-4-bora-3 a,4 a-diaza-s-indacene(BODIPY), functionalized at different positions with tetraphenylethylene(TPE), which is one of the most famous AIE luminogens. Thanks to this modification, we were able to tune the photoluminescence of the BODIPY moiety from the green to the near-infrared(NIR)spectral range and achieve PL efficiencies of ~50% in the solid state. Remarkably, we observed an enhancement of the AIE and up to ~100% photoluminescence efficiencies by blending the TPE-substituted BODIPY fluorophores with a poly[(9,9-di-noctylfluorene-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,7-diyl)](F8 BT) matrix. By incorporating these blends in organic lightemitting diodes(OLEDs), we obtained electroluminescence peaked in the range 650–700 nm with up to 1.8% external quantum efficiency and ~2 m W/cm2 radiance, a remarkable result for red/NIR emitting and solution-processed OLEDs.

Visible light communication with efficient far-red/near-infrared polymer light-emitting diodes

Visible light communication(VLC)is a wireless technology that relies on optical intensity modulation and is potentially a game changer for internet-of-things(IoT)connectivity.However,VLC is hindered by the low penetration depth of visible light in non-transparent media.One solution is to extend operation into the“nearly(in)visible”near-infrared(NIR,700-1000 nm)region,thus also enabling VLC in photonic bio-applications,considering the biological tissue NIR semitransparency,while conveniently retaining vestigial red emission to help check the link operativity by simple eye inspection.Here,we report new far-red/NIR organic light-emitting diodes(OLEDs)with a 650-800 nm emission range and external quantum efficiencies among the highest reported in this spectral range(>2.7%,with maximum radiance and luminance of 3.5 mW/cm^(2) and 260 cd/m^(2),respectively).With these OLEDs,we then demonstrate a“real-time”VLC setup achieving a data rate of 2.2 Mb/s,which satisfies the requirements for IoT and biosensing applications.These are the highest rates ever reported for an online unequalised VLC link based on solution-processed OLEDs.

Towards efficient near-infrared fluorescent organic light-emitting diodes

The energy gap law(E_(G)-law)and aggregation quenching are the main limitations to overcome in the design of near-infrared(NIR)organic emitters.Here,we achieve unprecedented results by synergistically addressing both of these limitations.First,we propose porphyrin oligomers with increasing length to attenuate the effects of the E_(G)-law by suppressing the non-radiative rate growth,and to increase the radiative rate via enhancement of the oscillator strength.Second,we design side chains to suppress aggregation quenching.We find that the logarithmic rate of variation in the non-radiative rate vs.E_(G)is suppressed by an order of magnitude with respect to previous studies,and we complement this breakthrough by demonstrating organic light-emitting diodes with an average external quantum efficiency of-1.1%,which is very promising for a heavy-metal-free 850 nm emitter.We also present a novel quantitative model of the internal quantum efficiency for active layers supporting triplet-to-singlet conversion.These results provide a general strategy for designing high-luminance NIR emitters.