A series of star-shaped molecules T(OCAn)Ps (n = 2–6) based on porphyrin as a core and oligocarbazole as monodisperse arms has been investigated by steady-state spectroscopy, femtosecond transient absorption (TA) spectroscopy, and quantum chemical calculations. UV–visible absorption spectra and quantum chemical calculation reveal that there is conjugation between the first carbazole units (the nearest to porphyrin) and porphyrin core but not between the neighboring carbazole units. The photo-excitation of T(OCAn)Ps results in efficient intramolecular energy transfer from the oligocarbazole (donor) to the porphyrin core (acceptor). The intramolecular energy-transfer time constants in T(OCAn)Ps (n = 2–6) obtained by global analysis of the femtosecond TA spectra are in the range of 0.60–22.27 ps. It is confirmed that the light-harvesting capability of porphyrin core could be improved by covalently linked oligocarbazole arms, while the excitation energy-transfer efficiency remains above 99%. This work provides a combined experimental-theoretical elucidation of ultrafast intramolecular energy-transfer processes, which could help develop novel star-shaped materials to achieve higher efficiency and better light-harvesting capability.

中文翻译：

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一系列具有中心卟啉核和四个寡咔唑臂的星形分子的分子内能量转移

通过稳态光谱，飞秒瞬态吸收（TA）光谱和量子，研究了一系列以卟啉为核心和低聚咔唑为单分散臂的星形分子T（OCA n）Ps（n = 2–6）化学计算。紫外可见吸收光谱和量子化学计算表明，第一个咔唑单元（最接近卟啉）和卟啉核心之间存在共轭，而相邻的咔唑单元之间没有共轭。T（OCA n）Ps的光激发导致分子内能量从低聚咔唑（供体）到卟啉核心（受体）的有效转移。T（OCA n）Ps（n中的分子内能量传递时间常数通过飞秒TA频谱的全局分析获得的= 2–6）在0.60–22.27 ps的范围内。证实了通过共价连接的低聚咔唑臂可以提高卟啉核的集光能力，同时激发能转移效率保持在99％以上。这项工作提供了超快的分子内能量转移过程的实验理论组合，可以帮助开发新颖的星形材料以实现更高的效率和更好的光收集能力。