Periodic Influences on the Charge‐Transfer and Radical Ion Pair Formation in Pnictogen‐Based Frustrated Lewis Pairs

Frustrated Lewis pairs (FLPs) can undergo single‐electron transfer (SET) via photoexcitation of an intermolecular charge–transfer (CT) band, thereby generating highly reactive radical ion pairs (RIPs) with the potential for homolytic CH bond activation. While the energetic position of CT bands is reasonably well understood in terms of donor ionization energies and acceptor electron affinities, systematic insight into the factors governing CT‐band intensity remains limited. Here, we investigate the influence of systematic pnictogen variation on CT excitation in archetypal triarylpnictogen/borane FLPs of the type PnMes 3 –B(C 6 F 5 ) 3 (Pn = P, As, Sb, Bi). Across the pnictogen series, all combinations exhibit CT bands in toluene and form the corresponding RIPs upon irradiation, as confirmed by UV–vis, EPR, and transient absorption spectroscopy. While CT‐band energies do not follow simple redox‐potential trends, DFT calculations reveal that the CT‐band intensity is governed by a combination of donor–acceptor orbital overlap, ground‐state charge–transfer mixing, and the thermodynamic stability of the encounter complex. In particular, increasing pnictogen–boron NBO overlap and enhanced dispersion interactions for the heavier pnictogens lead to markedly larger oscillator strengths and higher association constants. Together, these results establish design principles for tuning both the energy and intensity of CT excitation in FLPs for the rational generation of RIPs.