Photoinduced Charge Transfer State Probes the Dynamic Water Interaction with Metal–Organic Nanocages

Abstract

Kinetic stabilization of reactive photo-intermediates inside nanocages is conjectured to arise through a subtle interplay of cavity-induced hydrophobicity, cage electrostatics and solvent-mediated interactions. Herein we enunciate the dynamic role of the water shell around an electron deficient Pd 6 L 4 12+ nanohost by optically triggering the emergent host-guest charge transfer (CT) band arising from incarcerated guest 9-anthracenealdehyde (9-AA). Using time-resolved spectroscopy complemented with resonance Raman, we determine two temporal regimes of aqueous solvation i.e. ~120 fs and ~4 ps around the host-guest complex.Solvent-isotope dependent lifetime changes of the emissive twisted intramolecular charge transfer state for "caged" 9-AA unravels a slower ~1.65 ns water interaction through the exposed -CHO group. Our work provides the first comprehensive physical glimpse of all excited state water-mediated interactions, and thus motivates rational design of new reactions that would use the aqueous shell for supramolecular photochemistry.

Tuning the Ultrafast Dynamics of Photoinduced Proton-Coupled Electron Transfer in Energy Conversion Processes

“…This fast solvent response could be attributed to the relaxation of the first solvation shell following a perturbation to the local potential in the vicinity of the solute molecule. More recent experimental data on a photoinduced PCET system in a nanocage , implied that the dominant reaction coordinate for PT corresponds to reorganization of the first coordination shell of water around the nanocage on a time scale of 120 fs. This experimental observation is also consistent with the nonadiabatic dynamics simulations of photoinduced PCET in terms of the reorganization of the first solvation shell prior to PT and the approximate time scale for PT following photoexcitation to the S 1 state.…”

Ultrafast photoactivation of C─H bonds inside water-soluble nanocages

“…S33). Previous studies have established the dynamical blueshift observed for this coupled CT feature as a representative of the solvent rearrangement time scale in the photogenerated CT state ( 48 ). We find that, in 9-MA ⊂ Cage , solvent reorganization takes place in a biphasic manner with two time scales of ~900 fs and 4.2 ps (fig.…”

Self-assembly and photoinduced electron transfer in a donor- $$\upbeta $$ β -cyclodextrin-acceptor supramolecular system $$^{\S }$$ §

“…[1][2][3] Hydrogen bonding, π-stacking and metal-ligand coordination are the most common interactions utilized in the design of non-covalent D-A systems. [4][5][6][7][8][9][10][11][12][13][14] These interaction modes, however, are not very useful in assembling D-A systems in aqueous solutions. Biological electron transfers occur in aqueous environments and in this context those interactions capable of achieving D-A assembly in aqueous solutions assume greater significance.…”