Vinod Kavya, Noushad Najuma, Tanaka Hidetoshi, Mohan Nitha, Kokado Yuya, Tomiya Daiki, Kobori Yasuhiro, Hariharan Mahesh
School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram (IISER TVM) Maruthamala P. O., Vithura Thiruvananthapuram 695551 Kerala India
Department of Chemistry, Graduate School of Science, Kobe University 1-1 Rokkodaicho Nada-ku Kobe 657-8501 Japan.
Chem Sci. 2025 Jul 30. doi: 10.1039/d5sc02071a.
Exploring the impact of molecular aggregation on excited-state energy landscapes is key to tailoring long-lived delayed emission in organic materials. Here, we demonstrate aggregation-assisted energy gap modulation governing the balance between delayed fluorescence (DF) and room-temperature phosphorescence (RTP) in the indole-based hybrid charge-transfer emitters - HD and its brominated analogue BrD. In HD, J-aggregation, facilitated by a collinear molecular arrangement, significantly reduces the singlet-triplet energy gap ( ), enhances reverse intersystem crossing (RISC), and increases the efficiency of radiative decay from the regenerated singlet state, thereby favouring DF. In contrast, BrD forms H-aggregates through strong π-π interactions, which increase , suppress RISC and stabilize triplet excitons, resulting in prominent RTP. Time-resolved spectroscopy and theoretical calculations reveal that the hybridization of local-excited and charge-transfer states mediates excited-state evolution, with J-aggregation promoting DF and H-aggregation favouring RTP. These results establish a direct link between aggregation and distinct photoluminescence pathways, offering a strategy to tune delayed emission in organic materials.
探索分子聚集对激发态能量 landscapes 的影响是定制有机材料中长寿命延迟发射的关键。在此，我们展示了聚集辅助的能隙调制，它控制着基于吲哚的混合电荷转移发射体——HD 及其溴化类似物 BrD 中延迟荧光（DF）和室温磷光（RTP）之间的平衡。在 HD 中，由共线分子排列促进的 J-聚集显著降低了单重态-三重态能隙（ ），增强了反向系间窜越（RISC），并提高了从再生单重态的辐射衰减效率，从而有利于 DF。相比之下，BrD 通过强 π-π 相互作用形成 H-聚集体，这增加了 ，抑制了 RISC 并稳定了三重态激子，导致显著的 RTP。时间分辨光谱和理论计算表明，局域激发态和电荷转移态的杂化介导了激发态演化，J-聚集促进 DF，H-聚集有利于 RTP。这些结果在聚集与不同的光致发光途径之间建立了直接联系，为调节有机材料中的延迟发射提供了一种策略。
