Knowledge Bank

Analyses of phosphorescence spectra of tetraphenyl group IVA compounds $\psi 4X$ (where X = C, Si, Ge, Sn) at boiling liquid helium temperature will be presented. The phosphorescence (0, 0) transitions of the compounds in diluted mixed crystals are located as following:\begin{eqnarray*} (1)\psi_{4}C \ \ &in&\ \psi_{4}Si : 28,327, \quad \ in\ \psi_{4}Ge : 28,293, \qquad \ in\ \psi_{4}\ \ Sn : 28,249 \ (2) \psi_{4}Si\ &in&\ \psi_{4}Ge\ : 28,558, \quad \ in\ \psi_{4}Sn\ : 28,585, \ (3) \psi_{4}Ge\ &in&\ \psi_{4}Sn: 28,924, \ (4) \psi_{4}Sn\ &in&\ \psi_{4}Pb\ : 29,057 cm^{-1} \end{eqnarray*} The spectral shifts arising from the guest-host interactions are interpreted in terms of $\Pi$ bonding character, polarizability, etc. The results of concentration dependent studies on the system imply (1) the guest-guest interaction arises from the translationally equivalent sites; (2) the magnitude of the interaction depends on the structure of host crystal.