Institution: | 1. CNRS, CINaM UMR 7325, Aix Marseille Univ, Campus de Luminy, Case 913, 13288 Marseille, France;2. Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia, Euskadi, Spain
Kimika Fakultatea, Euskal Herriko Unibertsitatea (UPV/EHU), 20018 Donostia, Euskadi, Spain
Institut des Sciences Moléculaires (ISM, UMR CNRS 5255), University of Bordeaux, 351 Cours de la Libération, 33405 Talence, France;3. PPSM, ENS Paris Saclay, CNRS, Université Paris-Saclay, 94235 Cachan, France;4. Donostia International Physics Center (DIPC), Paseo Manuel de Lardizabal 4, 20018 Donostia, Euskadi, Spain;5. Institut des Sciences Moléculaires (ISM, UMR CNRS 5255), University of Bordeaux, 351 Cours de la Libération, 33405 Talence, France |
Abstract: | We describe the synthesis of a series of covalently linked dimers of quadrupolar curcuminoid-BF2 dyes and the detailed investigation of their solvent-dependent spectroscopic and photophysical properties. In solvents of low polarity, intramolecular folding induces the formation of aggregated chromophores, the UV/Vis absorption spectra of which display the optical signature characteristic of weakly-coupled H-aggregates. The extent of folding and, in turn, of ground-state aggregation is strongly dependent on the nature of the flexible linker. Steady-state and time-resolved fluorescence emission spectroscopies show that the Frenkel exciton relaxes into a fluorescent symmetrical excimer state with a long lifetime. Furthermore, our in-depth studies show that a weakly emitting excimer lies on the pathway toward a photocyclomer. Two-dimensional 1H NMR spectroscopy and density functional theory (DFT) allowed the structure of the photoproduct to be established. To our knowledge, this represents the first example of a 2π+2π] photodimerization of the curcuminoid chromophore. |