Fender, Nicolette S.,; Fronczek, Frank R.; John, Vijay; Kahwa, Ishenkumba A.; McPherson, Gary L.
Author Affiliation, Ana.
Chemistry; Faculty of Pure and Applied Sciences
Unusual luminescence spectra and decay dynamics in crystalline supramolecular [(A18C6)4MBr4][T1Br4]2 (A = Rb, K; M= 3d element) complexes
Date of Publication
Luminescence and electric energy transport characteristics of supramolecular cubic F23 [(A18C6)4MnBr4]-[T1Br4]2 complexes (A = Rb, 1; A = K, 2) were studied with the expectation that MnBr42- ions would be effective luminescent probes for solid state 18-crown-6 rotation-confrontational reorientation motion frequently revealed by NMR methods. Luminescence and excitation spectra of 1 are normal for complexes of MnBra42-, but complex 2 features an unusual orange emission (due tp crystal defects) with lmax » 570 nm which is sensitized by MnBr42- ions. Thermal barriers of 8 and 14kJ mol-1 (T< 210 K and T> 240 K, respectively) for 1 (MnBr42- lem = 511 nm) and 2 (crystal defect lem = 610 nm) are attributed to the energy required to bridge the Stokes shifted 4T1(4G) emission of the donor MnBr42- ions with the electronic origin of the 4T1(4G) state on the acceptor MnBr42- during energy migration. That of 26 kJ mol-1 (210 < t < 240 K) exhibited by 1 is attributed to the activation energy for the 18C6 solid state motion inferable from the single, broad featureless solid state 13C NMR band of [(K18C6)4ZnBr4][T1Br4]2 (3). Crystal data for [(K18C6)4MBr4][T1Br4]2, where M = Mn (Zn): space group F23 and Z = 4 for both complexes; a = 20.9862(7)) Å, V = 9242.8(3)) Å3, number of observed data = 672 (668), Rw = 0.037 (0.039), R = 0.062 (0.036)....