Garain Swadhin, Ansari Shagufi Naz, Kongasseri Anju Ajayan, Chandra Garain Bidhan, Pati Swapan K, George Subi J
New Chemistry Unit and School of Advanced Materials, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) Jakkur Bangalore 560064 India.
Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) Jakkur Bangalore 560064 India.
Chem Sci. 2022 Aug 10;13(34):10011-10019. doi: 10.1039/d2sc03343g. eCollection 2022 Aug 31.
Engineering the electronic excited state manifolds of organic molecules can give rise to various functional outcomes, including ambient triplet harvesting, that has received prodigious attention in the recent past. Herein, we introduce a modular, non-covalent approach to bias the entire excited state landscape of an organic molecule using tunable 'through-space charge-transfer' interactions with appropriate donors. Although charge-transfer (CT) donor-acceptor complexes have been extensively explored as functional and supramolecular motifs in the realm of soft organic materials, they could not imprint their potentiality in the field of luminescent materials, and it still remains as a challenge. Thus, in the present study, we investigate the modulation of the excited state emission characteristics of a simple pyromellitic diimide derivative on complexation with appropriate donor molecules of varying electronic characteristics to demonstrate the selective harvesting of emission from its locally excited (LE) and CT singlet and triplet states. Remarkably, co-crystallization of the pyromellitic diimide with heavy-atom substituted and electron-rich aromatic donors leads to an unprecedented ambient CT phosphorescence with impressive efficiency and notable lifetime. Further, gradual minimizing of the electron-donating strength of the donors from 1,4-diiodo-2,3,5,6-tetramethylbenzene (or 1,2-diiodo-3,4,5,6-tetramethylbenzene) to 1,2-diiodo-4,5-dimethylbenzene and 1-bromo-4-iodobenzene modulates the source of ambient phosphorescence emission from the CT excited state to LE excited state. Through comprehensive spectroscopic, theoretical studies, and single-crystal analyses, we elucidate the unparalleled role of intermolecular donor-acceptor interactions to toggle between the emissive excited states and stabilize the triplet excitons. We envisage that the present study will be able to provide new and innovative dimensions to the existing molecular designs employed for triplet harvesting.
调控有机分子的电子激发态能产生各种功能结果，包括环境三线态俘获，这在最近受到了极大关注。在此，我们介绍一种模块化的非共价方法，通过与合适的供体形成可调谐的“空间电荷转移”相互作用，来使有机分子的整个激发态势能面产生偏向。尽管电荷转移（CT）供体 - 受体复合物在软有机材料领域已作为功能和超分子基序得到广泛研究，但它们在发光材料领域尚未发挥出其潜力，这仍是一个挑战。因此，在本研究中，我们研究了一种简单的均苯四甲酸二酰亚胺衍生物与具有不同电子特性的合适供体分子络合时，其激发态发射特性的调制情况，以证明从其局域激发（LE）态、CT单重态和三线态选择性俘获发射光。值得注意的是，均苯四甲酸二酰亚胺与重原子取代且富电子的芳香供体共结晶，会产生前所未有的环境CT磷光，其效率令人印象深刻且寿命显著。此外，将供体的给电子强度从1,4 - 二碘 - 2,3,5,6 - 四甲基苯（或1,2 - 二碘 - 3,4,5,6 - 四甲基苯）逐渐降低到1,2 - 二碘 - 4,5 - 二甲基苯和1 - 溴 - 4 - 碘苯，可将环境磷光发射源从CT激发态调制到LE激发态。通过全面的光谱、理论研究和单晶分析，我们阐明了分子间供体 - 受体相互作用在发射激发态之间切换并稳定三线态激子方面的独特作用。我们设想，本研究将能够为现有的用于三线态俘获的分子设计提供新的创新维度。
