Organic lasing dyes possessing small energy gaps commonly suffer from high thresholds, because of energy-gap law, which induces detrimental nonradiative relaxation. Herein, molecules based on alternating donor (D) and acceptor (A) moieties are described. Those linear molecules are built with a spacer between D and A, with a general formula of D-spacer-A-spacer-D. Such modification of the A core allows one to obtain color-tunable lasing properties from yellow to near-infrared (NIR). Into more details, triphenylamine (TPA) is selected as the D moiety, while benzothiadiazole (BTD) and benzo[1,2-c:4,5c′]bis[1,2,5]thiadiazole (BBTD) with strong electron-withdrawing capability, are chosen as A cores for yellow ((TPA-F)2BTD) and NIR ((TPA-F)2BBTD) lasing dyes, respectively. Both dyes exhibit high photoluminescence quantum yields (PLQYs) and fast fluorescence radiative rate. The corresponding amplified spontaneous emission (ASE) thresholds of yellow and NIR dyes are as low as 0.5 and 3.8 μJ cm-2 in the solution-processing blending films, with wavelength peaks at 550 and 811 nm, respectively. In those dyes, the long alkyl chains appended on the fluorene conjugated spacer guarantee the high solubility and prevent aggregation. Consequently, for (TPA-F)2BTD, the neat film allows one to reach PLQYs as high as 90%, with a low ASE threshold (1.9 μJ cm-2) and good stability. Therefore, such promising molecular design allows the realization of color-tunable ASE or lasing dyes with very low thresholds.
Bibliographical noteFunding Information:
This study was financially supported by JST ERATO (Grant No. JPMJER1305) and Kyushu Organic Laser (KOALA) Tech, Inc. J.W.W. acknowledges NRF grant (Nos. 2017R1E1A1A01075394 and 2014M3A6B3063708)
This study was financially supported by JST ERATO (Grant No. JPMJER1305) and Kyushu Organic Laser (KOALA) Tech, Inc. J.W.W. acknowledges NRF grant (Nos. 2017R1E1A1A01075394 and 2014M3A6B3063708).
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