Arylamine-coumarin based donor-acceptor dyads: Unveiling the relationship between two-photon absorption cross-section and lifetime of singlet excited state intramolecular charge separation

Two-photon absorption (2 PA) with three-dimensional (3D) resolution and deep penetration of light into absorbing materials hold great promise for many applications such as 3D microscopy, 3D microfabrication, polymerization and optical data storage. We herein designed and synthesized two novel series of arylamine-coumarin based donor-acceptor dyads that showed good two-photon absorption activities. Tested by an open/close aperture Z-scan technique, the largest 2 PA cross-section value is 103.6 GM and the largest two-photon absorption coefficient (β) is 7.84 × 10⁻¹² cm W⁻¹. Fluorometric and electrochemical studies further reveal the formation of intramolecular charge transfer (ICT) among two dyads. Photoinduced singlet excited state intramolecular charge separation states were confirmed by ultrafast laser flash photolysis analyses coupled with TD-DFT excited state calculations. Surprisingly, the experimental measured lifetime of singlet excited state intramolecular charge separation state may be a diagnostic criterion for 2 PA cross-section of donor-acceptor systems. This work provides a new strategy for designing high-efficiency 2 PA materials.