Di‐benzoquinone Cyclopentadithiophene Diradicaloids Show Spin‐States Optical Transitions and Anomalous NIR Emission

We have prepared a series of bis(semiquinone) compounds with dithiophene bridges of different length that evolve from closed‐shell to full diradical character on the basis of the narrow singlet‐triplet energy gaps which allows the triplet population at 298 K for the longer compound. The medium size compound has a variety of photonic properties with absorptions and emission in the true NIR region mediated by a unique case of antikasha emission. A whole set of optical absorption and emission steady state and pico‐second transient absorption spectroscopies together with vibrational spectroscopies, spectroelectrochemistry and theoretical calculations have been carried our and subsequently interpreted.