Combining Benzotriazole and Benzodithiophene Host Units in Host–Guest Polymers for Efficient and Stable Near‐Infrared Emission from Light‐Emitting Electrochemical Cells. Issue 15 (16th May 2019) - Xiong, Wenjing
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. Abstract : Near‐infrared (NIR) emitting host–guest copolymers with different host units are synthesized, characterized and employed in light‐emitting electrochemical cells (LECs). The selection of host unit influences the LEC performance strongly, and the best NIR‐LEC delivers a second‐fast turn to a strong radiance >100 µW cm ‐2 at a low voltage of 3.6 V and a good operational stability of >350 h.