Combining Benzotriazole and Benzodithiophene Host Units in Host–Guest Polymers for Efficient and Stable Near‐Infrared Emission from Light‐Emitting Electrochemical Cells

Abstract

A set of host–guest copolymers with alternating benzodithiophene and benzotriazole (BTz) derivatives as host units and 4,7‐bis(5‐bromothiophen‐2‐yl)‐benzo[c][1,2,5]thiadiazole as the minority guest are synthesized, characterized, and evaluated for applications. A light‐emitting electrochemical cell (LEC) comprising such a host–guest copolymer delivers fast‐response near‐infrared (NIR) emission peaked at 723 nm with a high radiance of 169 µW cm−2 at a low drive voltage of 3.6 V. The NIR‐LEC also features good stability, as the peak NIR output only drops by 8% after 350 h of continuous operation. It is, however, found that the LEC performance is highly sensitive to the detailed chemical structure of the host backbone, and that the addition of electron‐donating thiophene bridging units onto the BTz unit is highly positive while the inclusion of fluorine atoms results in a drastically lowered performance, presumably because of the emergence of hydrogen bonding within the active material.

Deoxyribonucleic Acid as a Universal Electrolyte for Bio‐Friendly Light‐Emitting Electrochemical Cells

“…The TBABF 4 salt was replaced with its hexylated deriative THABF 4 , which was described to enable reliable LECs with a variety of emitters in literature. [54,59] In contrast to these investigations and previous electrochemical studies, [60,61] the THABF 4 salt and DNA-CTMA:THABF 4 SPE did not reveal a larger electrochemical window than TBABF 4 salt based SPEs (Figure 4a), which might originate in the catalytic properties of the Pt working electrode or electrochemical degradation of the solvent. Nonetheless, the oxidation and reduction onsets of the SPE matches the salt-only solution and is clearly not limited by the DNA-CTMA.…”

Non-toxic near-infrared light-emitting diodes

“…, demonstrated an LEC comprising a metal-free alternating copolymer as the emitter, delivering EL, emission peaked at 705 nm with a high radiance of 129 mW cm À2 (Tang et al, 2017). Very recently, Wang et al also studied a set of host-guest copolymers with alternating benzodithiophene and benzotriazole derivatives as host units and 4,7-bis(5-bromothiophen-2-yl)-benzo [c][1,2,5]thiadiazole as the minority guest (Xiong et al, 2019). Such host-guest copolymer emits at l max = 723 nm with an EQE of 0.135% in LEC device.…”

“…Very recently, Wang et al. also studied a set of host-guest copolymers with alternating benzodithiophene and benzotriazole derivatives as host units and 4,7-bis(5-bromothiophen-2-yl)-benzo[ c ][1,2,5]thiadiazole as the minority guest ( Xiong et al., 2019 ). Such host-guest copolymer emits at λ max = 723 nm with an EQE of 0.135% in LEC device.…”

Triethylene Glycol Substituted Diketopyrrolopyrrole‐ and Isoindigo‐Dye Based Donor–Acceptor Copolymers for Organic Light‐Emitting Electrochemical Cells and Transistors

“…[32,43] Besides the common advantages with OLEDs as organic electronic devices, firstly, LEC has a simpler device structure in which a single active layer, which generally comprises the organic semiconductor and mobile ions, is sandwiched between the air-stable anode and a cathode. [44] In addition, the applied voltage to the LEC device only needs to be larger than the bandgap of the OSC that is generally very low, therefore, it is a low-voltage technology that can greatly boost its application in wearable electronics. [45] Furthermore, theoretically, any essential emission colour can be obtained from LEC device.…”