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.

中文翻译：

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基于供体-间隔物-受体-间隔物-供体线性染料的从黄色到近红外（NIR）的彩色可调低阈值放大自发发射

具有能隙小的有机激光染料由于能隙定律通常遭受高阈值，这引起有害的非辐射弛豫。本文中，描述了基于交替的供体（D）和受体（A）部分的分子。这些线性分子在D和A之间带有一个间隔物，其通式为D–spacer–A–spacer–D。对A核的这种修饰使人可以获得从黄色到近红外（NIR）的颜色可调激光特性。更详细地讲，选择三苯胺（TPA）作为D部分，而苯并噻二唑（BTD）和苯并[1,2-c：4,5c']双[1,2,5]噻二唑（BBTD）具有强电子-提取能力，被选为黄色（（TPA-F）₂ BTD）和近红外（（TPA-F）₂BBTD）分别为激光染料。两种染料均显示出高的光致发光量子产率（PLQYs）和快速的荧光辐射速率。在溶液处理混合膜中，黄色和NIR染料的相应放大自发发射（ASE）阈值低至0.5和3.8μJcm ^-2，波长峰值分别在550和811 nm。在这些染料中，附加在芴共轭间隔基上的长烷基链可确保高溶解度并防止聚集。因此，对于（TPA-F）₂ BTD，整齐的薄膜可以使PLQYs高达90％，ASE阈值低（1.9μJcm ^-2），稳定性好。因此，这种有前途的分子设计允许实现具有非常低的阈值的颜色可调的ASE或激光染料。