(Invited) Understanding the Role of Chiral Bridges in Spin-Selective Photo-Induced Charge Transfer

Spin-controlled electrocatalysis, through the chiral induced spin selectivity (CISS) effect, offers a promising strategy for enhancing (photo-)electrocatalytic chemical reactions that have spin-dependent elementary steps such as the oxygen evolution reaction. By directing electrons through a chiral medium, the spin states of reaction intermediates can be selectively populated, which could lower reaction energy barriers and/or improve product selectivity. Currently, a significant gap remains in experimental data to guide the rational design of next generation chiral molecular (photo-)catalysts that effectively couple photons and the CISS effect through spin-selective photoinduced charge transfer. Toward this goal, we have synthesized torsionally-restricted biphenyls (BBPs) that exhibit thermally stable axial chirality as demonstrated through temperature-dependent HPLC. These chiral BBPs serve as molecular subunits for probing how optical activity and CISS emerge through electronic coupling across different bonding motifs between photosensitizer and chiral BBP element on mesoporous metal oxide scaffold. In one instance, we covalently couple a perylene photosensitizer to the chiral BBP through an acetylenic bridge and in the other, we assemble these two molecular structures through a metal-linking ion testing the influence of electronic coupling on spin selective charge transfer. We employ steady-state and time-resolved spectroscopies to interrogate how chirality is communicated between layers through chiral imprints in circular dichroism spectra and how photo-excited energy is transferred spin selectively within the system through hopping or tunneling mechanisms.