Unfiltered BroadbandProbes Can Obscure Long TimeDynamics in Populations Engaged in Second-Order Processes IncludingAnnihilation

Transient absorption (TA) is a powerful tool; however, this work demonstrates that common broadband probes can increase excited-state populations, leading to significant variations in excited-state observables in systems prone to second-order dynamics. Triplet–triplet annihilation is an important case where this might be a concern, possibly impacting developments in photon upconversion. TIPS-Anthracene is a model annihilator, boasting long lifetimes and high annihilation yields in solution. Herein, a greater than 3 ms lifetime is inadvertently more than halved during TA experiments utilizing a typical 100 W Xe arc-lamp probe. Without additional evidence, promising systems might be incorrectly assumed to be poor annihilation candidates. Alternatively, this lifetime suppression can manifest nonlinearly when calculating annihilation rates from measured threshold intensities, leading to large overestimates of this critical rate parameter. Modified experiment designs, such as probe filtering discussed here, are necessary for accurate assessment of long-time dynamics in populations prone to second-order decay.