Elucidation of complex triplet excited state dynamics in Pd( <scp>ii</scp> ) biladiene tetrapyrroles
Shea M. Martin, Gil M. Repa, Robert C. Hamburger, Craig A. Pointer, Kaytlin Ward, Trong-Nhan Pham, Maxwell I. Martin, Joel Rosenthal, Lisa A. Fredin, Elizabeth R. Young
Abstract
= 550 nm). Each Pd(II) biladiene complex displayed an intersystem crossing lifetime on the order of tens of ps and a triplet lifetime of ∼20 μs, regardless of the excitation wavelength. However, when higher-energy light is used to excite the complexes, a new lifetime on the order of hundreds of ps is observed. The origin of the 'extra' lifetime observed upon higher energy excitation was revealed using density functional theory (DFT) and time-dependent DFT (TDDFT). These efforts demonstrated that excitation into higher-energy metal-mixed-charge-transfer excited states with high spin-orbit coupling to higher energy metal-mixed-charge-transfer triplet states leads to the additional excitation deactivation pathway. The results of this work demonstrate that Pd(II) biladienes support a unique triplet photochemistry that may be exploited for development of new photochemical schemes and applications.