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Abstract The electronic, optical, and solid state properties of a series of monoradicals, anions and cations obtained from starting neutral diradicals have been studied. Diradicals based ons‐indacene and indenoacenes, with benzothiophenes fused and in different orientations, feature a varying degree of diradical character in the neutral state, which is here related with the properties of the radical redox forms. The analysis of their optical features in the polymethine monoradicals has been carried out in the framework of the molecular orbital and valence bond theories. Electronic UV‐Vis‐NIR absorption, X‐ray solid‐state diffraction and quantum chemical calculations have been carried out. Studies of the different positive‐/negative‐charged species, both residing in the same skeletalπ‐conjugated backbone, are rare for organic molecules. The key factor for the dual stabilization is the presence of the starting diradical character that enables to indistinctively accommodate a pseudo‐hole and a pseudo‐electron defect with certainly small reorganization energies for ambipolar charge transport.
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Learning how to fine‐tune diradical properties by structure refinement
Abstract The literature has seen a large increase in the number of new carbon‐based organic diradicals/diradicaloids in recent years. While a plethora of new and exciting structures have been created, there seemingly is a gap in knowledge of what fundamental electronic parameters are in play and thus how to rationally manipulate said parameters to “fine tune” the resultant diradical properties. Since 2014, the Haley group has been exploring methods to systematically alter the diradical character and the singlet‐triplet energy gap in said class of molecules. Our entrance into organic diradicals began with the π‐expansion of the benzene core of indeno[1,2‐b]fluorene up to the anthracene core of diindenoanthracene (DIAn). DIAn possessed moderate diradical character (y =0.62) with a surprising level of stability (more than 2 months in solution). From this molecular blueprint for producing stable diradicals, the Haley lab has investigated how to fine tune diradical properties via structural changes in two key positions: (a) the length of the acene core and (b) thoughtful exchange of the outer arenes. With this strategy at our disposal, we can make large scale changes to the diradical character index and singlet‐triplet energy gap through changing the core length, and these properties can be further fine‐tuned in a series of closely related diradicals by careful exchange of the outer arenes utilizing the straightforward methods described in this mini‐review.
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- Award ID(s):
- 1954389
- PAR ID:
- 10457013
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Physical Organic Chemistry
- Volume:
- 33
- Issue:
- 11
- ISSN:
- 0894-3230
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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