Rates of Electronic Excitation Hopping in Anisotropic Ionic Crystals of [Ru(2,2‘-bipyridine)₃]X₂ (X = ClO₄^-, PF₆^-, SbF₆^-); Monte Carlo Simulation of Single- and Multi-Exponential Emission Decays

Abstract

Emission decays of triplet metal-to-ligand charge transfer states in anisotropic crystals of [Ru(1 - x)Os(x)(bpy)(3)]X(2) (bpy = 2,2'-bipyridine, X = PF(6)-, ClO(4)-, SbF(6)-, and 0.115 > x > 0.001) at approximately 300 K were measured by means of time-correlated single-photon counting. Rates of excitation hopping calculated on the basis of an interaction between transition dipoles of a donor cation and an acceptor cation are insufficient to simulate the single-exponential decays (x = 0.0099) and the multiexponential decays (x = 0.060 and 0.115) of the PF(6)- salt crystals. A limiting rate of excitation hopping to an imaginary cation at the van der Waals distance via a super-exchange interaction between d orbitals through the bpy ligands was determined to be 0.83 x 10(10) s(-1) on average by means of a step-by-step Monte Carlo simulation, assuming an distance-attenuation factor, beta, of the exchange interaction of 10 nm-1. The total rate of excitation hopping via both a dipole-dipole mechanism and a super-exchange mechanism to the neighboring sites of the cation was calculated to be 5.4 x 10(9) s(-1) for the PF(6)- crystal. Anisotropic diffusion constants estimated from the hopping rates and lengths in the PF(6)- crystal are 9.3 x 10(-6), 9.1 x 10(-6), and 1.4 x 10(-6) cm(2)s(-1) along the a axis, the b axis, and the c axis, respectively, which are compared with an isotropic diffusion constant, 1.3 x 10(-6) cm(2) s(-1), estimated from the pseudo-bimolecular rate constant of excitation transfer to [Os(bpy)(3)](2+), using an isotropic Smoluchowski equation. A multiexponential emission decay of [Ru(0.885)Os(0.115)(bpy)(3)](PF(6))(2) was also simulated to determined the limiting rate of excitation transfer to [Os(bpy)(3)](2+) at the van der Waals distance (2.6 x 10(11) s(-1)). The magnitude of beta determined is 6.5 and 11.5 nm(-1) for the ClO(4)- and the SbF(6)- salt crystals, respectively, on reference to that of beta (10 nm(-1)) for the PF(6)- salt crystal.

Series of C^N^C Cyclometalated Pt(II) Complexes: Synthesis, Crystal Structures, and Nonlinear Optical Properties in the Near-Infrared Region

“…In comparison to the later stages, the more rapid initial decay can be attributed to the excitation transfer to cations of Pt­(C^N^C) + . The possibility of Pt-1 and Pt-2 triplet–triplet annihilation is excluded because the excitation laser intensity was too low to cause it . The TA of Pt­(II) complexes decays monoexponentially in the range 280–760 nm, indicating that the TA arises from the excited state.…”

Polymorph Control of Luminescence Properties in Molecular Crystals of a Platinum and Organoarsenic Complex and Formation of Stable One-Dimensional Nanochannel

“…Emission and excitation spectra were obtained on an FP-8500 (JASCO). The luminescence decay time of the crystalline solid was obtained using a least-squares method for time courses of luminescence recorded by a correlated single-photon counting method using a femtosecond Ti 3+ :sapphire laser (400 nm) with a cavity dumper (∼10 kHz) …”

Study of Energy Transfer and Triplet Exciton Diffusion in Hole‐Transporting Host Materials

“…Since the lifetime of phosphorescence among these host molecules are comparable, the diffusion length should depend solely on D. The diffusion coefficient is proportional to the rate constant for triplet energy transfer, k, according to Equation 2. [35] k ¼ 4pDR eff N 0 (2) Here, R eff is the largest collision diameter for the two molecules undergoing triplet energy transfer and N 0 is Avogadro's number. In addition, the rate constant, k, should follow the Golden Rule given in Equation 3 for a nonadiabatic process in a weakly coupled system.…”