Fig. 4. (A) Transient absorption spectra measured with Vs and Cage in tetrahydrofuran (THF) upon excitation at 375 nm. (B) Comparison of the residual signals (≥100 ps) of Vs and Cage attributed to the ³CSS and to the T₁ state populated upon triplet sensitization of Cage with tris(bipyridine)ruthenium(ii) chloride (Ru-bpy). (C) Energy-level scheme summarising the dynamics upon photo-population of the S₁(π–π*) state and timescales deduced from the transient absorption measurements (bottom). The spin–orbit charge-transfer intersystem crossing (SOCT-ISC) channel is only operative if the frontier molecular orbitals localised on the donor and acceptor sub-units are restricted to a near-perpendicular orientation.