Abstract:Doing the hula twist? A photochemically stimulated inversion of an sp(2)-hybridized oxygen atom upon simultaneous rotation of two adjacent bonds may be possible in a pure singlet excited potential energy surface in uninhibited fluid media (see scheme).
“…These results suggest that there are two N* populations with different decay times but similar emission spectra, which might be ascribed to two different conformers of the neutral form N*. Based on the similar behavior found for methoxy derivatives of naphthalene [76,77], anthracene [78], and N-methylquinolinium [79], we tentatively assign the emissive species to the syn and anti conformers originated by methoxy group rotation in CBTOMe (Fig. 5), but recognize that other intramolecular changes may also be present.…”
Section: Photoacid Character Of the Cbtoh Hydroxyl Groupsupporting
“…These results suggest that there are two N* populations with different decay times but similar emission spectra, which might be ascribed to two different conformers of the neutral form N*. Based on the similar behavior found for methoxy derivatives of naphthalene [76,77], anthracene [78], and N-methylquinolinium [79], we tentatively assign the emissive species to the syn and anti conformers originated by methoxy group rotation in CBTOMe (Fig. 5), but recognize that other intramolecular changes may also be present.…”
Section: Photoacid Character Of the Cbtoh Hydroxyl Groupsupporting
“…Consequently, Saltiel and co-workers have recently refuted earlier claims of HT evidences and identified the intermediate photoproducts as the result of simple DBIs 17 , 50 , 51 . The question whether a possible HT mechanism is an intrinsic property of the molecule itself 18 or on the contrary is dictated mainly by outside restrictions 52 , 53 (e.g., imposing volume conservation 16 , 54 during the motion) is even less resolved. Fig.…”
Photoisomerization reactions are quintessential processes driving molecular machines and motors, govern smart materials, catalytic processes, and photopharmacology, and lie at the heart of vision, phototaxis, or vitamin production. Despite this plethora of applications fundamental photoisomerization mechanisms are not well understood at present. The famous hula-twist motion—a coupled single and double-bond rotation—was proposed to explain proficient photoswitching in restricted environments but fast thermal follow-up reactions hamper identification of primary photo products. Herein we describe an asymmetric chromophore possessing four geometrically distinct diastereomeric states that do not interconvert thermally and can be crystallized separately. Employing this molecular setup direct and unequivocal evidence for the hula-twist photoreaction and for photoinduced single-bond rotation is obtained. The influences of the surrounding medium and temperature are quantified and used to favor unusual photoreactions. Based on our findings molecular engineers will be able to implement photo control of complex molecular motions more consciously.
“…For example a family of methoxynaphthalenes incorporated in cyclodextrins undergoes a volume conserving isomerization reaction which is not observed in free solution. 163,164 This effect thus offers a degree of control over the structure of the photoproduct. Such volume conserving pathways (such as ''crankshaft motion'' and ''hula twist'') which contrast with the solvent displacing ''one-bond flip'' rotation about a single bond, had earlier been shown to be important for isomerization reactions in glassy media, but are generally thought to proceed over higher activation barriers barriers.…”
Section: Other Excited State Reactions In Micellesmentioning
Time resolved fluorescence follows reaction dynamics in real-time. Study of reaction which are sensitive to their environment allowed the effect of confinement to be observed and studied.
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