Executive Summary : | Organic diradicaloids, both Kekulé and non-Kekulé, have potential applications in various fields such as organic optoelectronics, energy storage, molecule-based magnets, and NIR active materials. Kekulé diradicaloids often exhibit singlet ground states, while non-Kekulé diradicaloids show triplet ground states when spin-centers are connected in a non-disjoint manner. Some Kekulé diradicaloids, such as Zethrenes, Thiele-Tschitschibabin hydrocarbons, and triangulene-diradicals, require extended PAH motifs or bulky mesityl groups to protect the radical centers and gain stability. However, there are few reports of non-Kekulé diradicaloids due to design and synthesis difficulties. The current proposal aims to address these issues by developing new diradicaloids. Non-Kekulé diradicaloids are created by conjugating a planar persistent radical with an electroactive unit that is either electro(chemically)-oxidized or reduced to generate a second radical center reversibly. These two radical bearing π-units couple ferromagnetically rather than via resonance. In the case of Kekulé diradicaloids, new double helical quinodimethanes (hQDMs) are created, which involve integrating the QDM moiety in a double helicene structure. The chiroptical properties of hQDMs are tuned by systematically changing the π-terminals on the helicene skeleton. CV, VT-NMR, EPR, and SQUID are used to investigate the diradical properties of both Kekulé and non-Kekulé diradicaloids. Circular dichroism techniques are used to investigate the chiroptical properties of hQDMs. Extensive density functional theory (DFT) calculations are used to support the experimental results and visualize the spin-delocalization and other properties of these diradicaloids. |