Correlation between the strength of conjugation and spin-spin interactions in stable diradicaloids

Diradicaloids are emerging materials for organic electronics and spintronics, and therefore understanding the correlation between their physical properties and the strength of conjugation effect is important. Herein, we report a systematic study of three Blatter based diradicaloids with different conjugated bridges such as twisted p -diphenyl ( DPh-D ), locked fluorenyl ( FDT ) and fused naphthyl ( Nap-D ). All these molecules possess an open-shell singlet ground state. Their diradical character decreases from DPh-D to Nap-D (0.44 to 0.14). Meanwhile, their corresponding singlet-triplet energy gaps increase from −1.27 to −1.54 kcal mol −1 . However, the magnetic properties in the solid state are heavily affected by molecular stacking, the close 1-D chain π-π stacking in FDT gives a high-spin quintet state. Overall, we have observed that the better the conjugation the stronger the spin-spin interaction in diradicaloids, which also significantly influence their physical properties. Blatter based diradicaloids with p -diphenyl, fluorenyl and naphthyl bridges exhibit bridge dependent magnetic and optical properties.