Cationic Exciplexes: Role of Hydrogen Bonding in Deactivation and Electronic Coupling

Emissive properties for the cationic exciplex (A⁺ */D→A^. D^.+ ) of an isoquinolinium cation tethered to a substituted arene (1⁺ ) are strongly affected by hydrogen bonding solvents. At equal dielectric constant (ϵ), the ground-to-excited state energy gaps (ΔG) and solvent reorganization energies (λ_s ) decrease from nitriles to aliphatic alcohols. The corresponding decrease from aliphatic alcohols to high hydrogen bond acidity solvents is ∼3 times larger. The exciplex decay (k_Ex ), largely determined by unfolding of the exciplex to a stretched conformer, changes in a complex way depending on the strength of the hydrogen bond ability of these solvents. In contrast, the electronic couplings between the exciplex ground, excited, and charge transfer states do not show a solvent functionality dependence.