Dual Fluorescence through Kasha’s Rule Breaking: An Unconventional Photomechanism for Intracellular Probe Design

• DOI: 10.1021/acs.jpcb.5b01119
• Publication Date: 2015-04-22T18:43:09Z
• Authors: Giuseppe Brancato; Giovanni Signore; Paolo Neyroz; Dario Polli; Giulio Cerullo; Gerardo Abbandonato; Luca Nucara; Vincenzo Barone; Fabio Beltram; Ranieri Bizzarri
• Keywords: Models, Molecular; Microscopy, Confocal; Dual Fluorescence through Kasha's Rule Breaking: An Unconventional Photomechanism for Intracellular Probe Design; Physical and Theoretical Chemistry; Materials Chemistry2506 Metals and Alloys; Surfaces, Coatings and Films; Molecular Conformation; Electrons; Fluorescence Polarization; Biosensing Techniques; 01 natural sciences; Cell Line; 0104 chemical sciences; Coumarins; dual fluorescence, molecular sensors, Anti-Kasha dual emission mechanism; Humans; Fluorescent Dyes

Dual fluorescence is an anomalous photophysical phenomenon observed in very few chromophores in which a two-color radiative process occurs that involves two distinct excited electronic states. To date its observation was linked either to electronic rearrangement of an excited fluorophore leading to two conformers with distinct emissive properties, or to a photochemical modification leading to different fluorescent species. In both cases, emission originates from the lowest excited state of the resulting molecular configurations, in line with the so-called Kasha's rule. We report here a combined theoretical and spectroscopic study showing, for the first time, an anti-Kasha dual-emission mechanism, in which simultaneous two-color emission takes place from the first and second excited state of a coumarin derivative. We argue that the observed environmental sensitivity of this peculiar optical response makes the present compound ideally suited for biosensing applications in living cells.