Busby Erik, Xia Jianlong, Low Jonathan Z, Wu Qin, Hoy Jessica, Campos Luis M, Sfeir Matthew Y
†Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027, United States.
‡Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, United States.
J Phys Chem B. 2015 Jun 18;119(24):7644-50. doi: 10.1021/jp511704r. Epub 2015 Feb 5.
A common synthetic strategy used to design low-bandgap organic semiconductors employs the use of "push-pull" building blocks, where electron -rich and electron-deficient monomers are alternated along the π-conjugated backbone of a molecule or polymer. Incorporating strong "pull" units with high electron affinity is a means to further decrease the optical gap for infrared optoelectronics or to develop n-type semiconducting materials. Here we show that the use of thiophene-1,1-dioxide as a strong acceptor in "push-pull" oligomers affects the electronic structure and carrier dynamics in unexpected ways. Critically, the overall excited-state lifetime is reduced by several orders of magnitude relative to unoxidized analogs due to the introduction of low-energy optically dark states and low-energy triplet states that allow for fast internal conversion and intramolecular singlet fission. We found that the electronic structure and excited-state lifetime are strongly dependent on the number of sequential thiophene-1,1-dioxide units. These results suggest that both the static and dynamical optical properties are highly tunable via small changes in chemical structure that have drastic effects on the optoelectronic properties, which can impact the types of applications that involve these materials.
一种常用于设计低带隙有机半导体的合成策略是采用“推-拉”结构单元，其中富电子和缺电子单体沿着分子或聚合物的π共轭主链交替排列。引入具有高电子亲和力的强“拉”单元是进一步降低红外光电子器件光学带隙或开发n型半导体材料的一种方法。在此，我们表明，在“推-拉”低聚物中使用噻吩-1,1-二氧化物作为强受体，会以意想不到的方式影响电子结构和载流子动力学。至关重要的是，由于引入了低能量的光学暗态和低能量的三重态，使得快速内部转换和分子内单重态裂变成为可能，相对于未氧化的类似物，整体激发态寿命降低了几个数量级。我们发现电子结构和激发态寿命强烈依赖于连续噻吩-1,1-二氧化物单元的数量。这些结果表明，静态和动态光学性质均可通过化学结构的微小变化进行高度调节，而这种变化会对光电性质产生显著影响，进而可能影响涉及这些材料的应用类型。
