Papadopoulos Ilias, Reddy S Rajagopala, Coto Pedro B, Lehnherr Dan, Thiel Dominik, Thoss Michael, Tykwinski Rik R, Guldi Dirk M
Department of Chemistry and Pharmacy & Interdisciplinary Center for Molecular Materials (ICMM), Friedrich Alexander-University Erlangen-Nuremberg, Egerlandstraße 3, 91058 Erlangen, Germany.
Department of Chemistry, School of Chemical Sciences and Pharmacy, Central University of Rajasthan, NH-8, Bandarsindri, Ajmer, Rajasthan 305817, India.
J Phys Chem Lett. 2022 Jun 2:5094-5100. doi: 10.1021/acs.jpclett.2c01395.
We placed two pentacene chromophores at the termini of a diacetylene linker to investigate the impact of excitation wavelength, conformational flexibility, and vibronic coupling on singlet fission. Photoexcitation of the low-energy absorption results in a superposed mixture of states, which transform on an ultrafast time-scale into a spin-correlated and vibronically coupled/hot delocalized triplet pair (TT). Regardless of temperature, the lifetime for (TT) is less than 2 ps. In contrast, photoexcitation of the high-energy absorption results in the formation of (TT) lasting 1.0 ps, which then decays at room temperature within 4 ps via triplet-triplet annihilation. Lowering the temperature enables (TT) to delocalize and vibronically decouple, in turn affording (TT). In addition, our results suggest that the quasi-free rotation at the diacetylene spacer may lead to twisted conformations with very low SF quantum yields, highlighting the need of controlling this structural aspect in the design of new singlet fission active molecules.
我们将两个并五苯发色团置于二乙炔连接体的末端，以研究激发波长、构象灵活性和振动耦合对单线态裂变的影响。低能吸收的光激发会产生叠加的态混合物，这些态在超快时间尺度上转变为自旋相关且振动耦合/热离域的三重态对（TT）。无论温度如何，（TT）的寿命都小于2皮秒。相比之下，高能吸收的光激发会导致形成持续1.0皮秒的（TT），然后在室温下通过三重态-三重态湮灭在4皮秒内衰减。降低温度会使（TT）离域并振动解耦，进而产生（TT）。此外，我们的结果表明，二乙炔间隔基处的准自由旋转可能导致具有极低单线态裂变量子产率的扭曲构象，这突出了在设计新的单线态裂变活性分子时控制这一结构方面的必要性。
