Majumder Kanad, Mukherjee Soham, Park Jungjin, Kim Woojae, Musser Andrew J, Patil Satish
Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore, 560012, India.
Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York, 14853, USA.
Angew Chem Int Ed Engl. 2024 Dec 20;63(52):e202408615. doi: 10.1002/anie.202408615. Epub 2024 Nov 18.
Various analogues of the alkylsilylacetylene group are frequently used as auxiliary groups to enhance the solubility and stability of the acene dimer core, widely used as platforms to investigate intramolecular singlet fission (iSF) mechanisms. However, while in the 2,2'-linked dimers they are primarily auxiliary groups, these are essential fragments of the bridging units in 6,6'/5,5'-linked dimers, the two preferred choices for dimerization. The starkly different iSF dynamics observed in the two variants raise the question of what role the acetylene bridges play. Here, we systematically designed a set of (oligo-)para-phenylene bridged 2,2'-linked pentacene dimers with an additional acetylene fragment in the bridging unit to mimic the structure of 6,6'-linked dimers. Contrasting the results with previously reported analogous 2,2'-linked and 6,6'-linked pentacene dimers reveals that the acetylene bridges contribute to significant conformational freedom. This effect provides a mechanism to promote spin evolution within the triplet pair to achieve free triplets but also offers new parasitic pathways for triplet-pair recombination, revealing that this structural motif can be both a boon and a nuisance. Additionally, our analysis reveals that these bridges directly modify the electronic states, highlighting significant pitfalls of the standard chromophore-bridge-chromophore framework used to design and interpret photophysics of iSF materials.
烷基硅乙炔基团的各种类似物经常被用作辅助基团，以提高并苯二聚体核心的溶解性和稳定性，该核心被广泛用作研究分子内单线态裂变（iSF）机制的平台。然而，在2,2'-连接的二聚体中它们主要是辅助基团，而在6,6'/5,5'-连接的二聚体中，这些基团是桥连单元的关键片段，这两种二聚体是二聚化的首选。在这两种变体中观察到的截然不同的iSF动力学引发了乙炔桥起什么作用的问题。在这里，我们系统地设计了一组（寡）对亚苯基桥连的2,2'-连接的并五苯二聚体，其桥连单元中有一个额外的乙炔片段，以模拟6,6'-连接的二聚体的结构。将结果与先前报道的类似的2,2'-连接和6,6'-连接的并五苯二聚体进行对比，结果表明乙炔桥有助于显著的构象自由度。这种效应提供了一种机制，可促进三重态对中的自旋演化以实现自由三重态，但也为三重态对的重组提供了新的寄生途径，这表明这种结构基序既可能是一种优势，也可能是一种麻烦。此外，我们的分析表明，这些桥直接改变了电子态，突出了用于设计和解释iSF材料光物理的标准发色团-桥-发色团框架的重大缺陷。
