BO21 as a Molecular Rotor?

The cationic dye BO21 has some unusual fluorescent properties, which we studied in this recent report in Photochemical and Photobiological Sciences.[1] The effects of glycerol - and thus vicosity - on the fluorescent properties suggest that BO21 is a molecular rotor. This hypothesis is supported by DFT and TDDFT calculations that show that in the first excited state there may be rotation to a twisted intramolecular charge transfer (TICT) state that may allow for a radiationless transition to the ground state. The affects of various physical parameters on the fluorescent properties, as well as the effect of heparin, suggest that BO21 may have potential as a sensor in biological contexts.

[1] Eizig Bar-On, Z.; Iron, M. A.; Kasdan, H.; Amir, D.; Afrimzon, E.; Zurgil, N.; Moshkov, S.; Deutsch, M., "The Cationic Dye Basic Orange 21 (BO21) as a Potential Fluorescent Scensor," Photochemical and Photobiological Sciences 2018, 17(10), 1417-1428. http://dx.doi.org/10.1039/C7PP00455A