A diradical approach to obtain stable organic dyes with intense absorption around λ=1100 nm is reported. The para- and meta-quinodimethane-bridged BODIPY dimers BD-1 and BD-2 were synthesized and were found to have a small amount of diradical character. These molecules exhibited very intense absorption at λ=1088 nm (ɛ=6.65×105 M−1 cm−1) and 1136 nm (ɛ=6.44×105 M−1 cm−1), respectively, together with large two-photon-absorption cross-sections. Structural isomerization induced little variation in their diradical character but distinctive differences in their physical properties. Moreover, the compounds showed a selective fluorescence turn-on response in the presence of the hydroxyl radical but not with other reactive oxygen species.
Ni, Y., Lee, S., Son, M., Aratani, N., Ishida, M., Samanta, A., Yamada, H., Chang, Y. T., Furuta, H., Kim, D., & Wu, J. (2016). A Diradical Approach towards BODIPY-Based Dyes with Intense Near-Infrared Absorption around λ=1100 nm. Angewandte Chemie - International Edition, 55(8), 2815-2819. https://doi.org/10.1002/anie.201511151