The Observation of Interchain Motion in Self-Assembled Crystalline Platinum(II) Complexes: An Exquisite Case but By No Means the Only One in Molecular Solids

Abstract

In organic and organometallic solids, upon electronic excitation, most intermolecular structural relaxations follow a pathway along the π−π stacking direction or metal−metal bond with significant coupling strength. Differently, we discovered that the selfassembled platinum(II) complexes, Pt(fppz) 2 , exhibit an unusual interchain contraction. The ground-state and excited-state multiple local minima were distinguished by temperaturedependent excitation/emission spectra, indicating the existence of multiple local minima. The time-resolved emission decay revealed the excited-state structural relaxation lifetime with τ obs = 41 ns at 298 K. Temperature-dependent X-ray diffraction analysis showed that the packing geometries contract 0.6 Å along the interchain direction (a-axis) at 50 K compared to the geometries at 298 K. Such structural displacements render the slow internal conversion rate in the excited states. We thus demonstrate the correlation between the packing geometries and the excited-state dynamics of the self-assembled Pt(II) complexes, shedding light on the unique direction of interchain structural deformation of the molecular aggregates.

Photoinduced Aryl Transfer from Imidazolyl-Quinoline π-Conjugated Systems

“…This slow reaction behavior was ascribed to photoinduced intramolecular structural planarization (PISP) with an activation barrier as large as 8 kcal/mol due to steric hindrance. 58 For the case in point of a small frequency factor, Su et al discovered a precursor−successor relationship in Pt(fppz) 2 film by resolving a 40 ns lifetime for the structural relaxation, 59 yet the temperature-dependent analysis showed only a 1.3 kcal/mol activation barrier; however, the reaction frequency factor is measured to be as low as 10 8 s −1 .…”