Excited-State Dynamics Achieved Ultimate Stereocontrol of Photocyclodimerization of Anthracenecarboxylates on a Glucose Scaffold

Abstract

Near-perfect stereoselectivity was attained in the diastereodifferentiating [4 + 4] photocyclodimerization of 2-anthracenecarboxylates tethered to a glucose scaffold not by thermodynamically tuning the conformer equilibrium in the ground state but by kinetically controlling the conformer dynamics and reactivity in the excited state, which enabled us, after removal of the scaffold, to obtain a single enantiomer of chiral anti-head-to-head-cyclodimer in >99% optical and 96% chemical yield from an ensemble of four precursor conformers.

Enantiodifferentiating Photodimerization of a 2,6‐Disubstituted Anthracene Assisted by Supramolecular Double‐Helix Formation with Chiral Amines

“…By comparison with the experimental results (22:78 and +30 % ee (( P )‐ anti ‐ 2 rich) at 25 °C and 57:43 and −98 % ee (( M )‐ anti ‐ 2 rich) at −35 °C, respectively; runs 6 and 9 in Table ), the calculated anti / syn ratio and highly ( M )‐ anti ‐ 2 enantioselectivity at −35 °C were in roughly agreement with the observed ones, but those at 25 °C disagree with the experimental results. Hence, as in the case for the photodimerization of 1 , we may conclude that the enantioselectivity of the chiral anti ‐ 2 photodimer as well as the diastereoselectivity of the anti ‐ 2 and syn ‐ 3 mostly result from the difference in the excited‐state reactivities of the diastereomeric right‐ and left‐handed double‐helical inclusion complexes (( 1 ) 2 ⋅(( R )‐ 4 ) 4 ) rather than the difference in their ground‐state stabilities . However, the reasons for poor anti ‐ 2 / syn ‐ 3 selectivity and highly temperature‐dependent enantioselectivity of anti ‐ 2 with accompanying inversion of the product chirality at 25 °C during the photodimerization of 1 in the presence of chiral amines remain unclear, which may not be completely explained by the difference in the excited‐state reactivities based on the calculation results of the ground‐state stabilities.…”

Smart Fluorescence Materials that Are Controllable by Hydrostatic Pressure: Peptide−Pyrene Conjugates

“…As can be seen from Figure 5b,c with Table 1, intriguingly, the rise component (10-12 ns) was found with the excimer in the same wavelength region. This may be assignable to the "frustrated" excimer [58] or the so-called second excimer [59] which is a precursor of a fully-overlapped sandwich excimer. The decay profile for the rise seems to be clearer by comparing to that observed in the monomer fluorescence decay of Figure 5a.…”

Ice Confinement-Induced Solubilization and Aggregation of Cyanonaphthol Revealed by Fluorescence Spectroscopy and Lifetime Measurements

“…The lifetime of the excited species (7.3 ns) is slightly longer than that of RO – * and exists at approximately 360 nm. Therefore, we assigned the fifth excited species to an excimer [ROH·ROH]* that was not detected in the solutions. − The excimer formation should be facilitated by the enhanced solubility of 6CN upon freezing. In fact, in the other frozen state (α = 22, and c 6CN FCS = 10 mM) the fluorescence lifetime decays (Figure c) also showed the formation of the aggregates (τ 1 ; 0.24–0.58 ns) and the excimer species (τ 5 ; 9.1–14 ns) along with the others (τ 2–4 ), indicating the effect of concentration even at relatively low α.…”