Understanding the Origin of Phosphorescence in Bismoles: A Synthetic and Computational Study

A series of bismuth
heterocycles, termed bismoles, were synthesized via the efficient
metallacycle transfer (Bi/Zr exchange) involving readily accessible
zirconacycles. The luminescence properties of three structurally distinct
bismoles were explored in detail via time-integrated and time-resolved
photoluminescence spectroscopy using ultrafast laser excitation. Moreover,
time-dependent density functional theory computations were used to
interpret the nature of fluorescence versus phosphorescence in these
bismuth-containing heterocycles and to guide the future preparation
of luminescent materials containing heavy inorganic elements. Specifically,
orbital character at bismuth within excited states is an important
factor for achieving enhanced spin–orbit coupling and to promote
phosphorescence. The low aromaticity of the bismole rings was demonstrated
by formation of a CuCl π-complex, and the nature of the alkene-CuCl
interaction was probed by real-space bonding indicators derived from
Atoms-In-Molecules, the Electron Localizability Indicator, and the
Non-Covalent Interaction index; such tools are of great value in interpreting
nonstandard bonding environments within inorganic compounds.