Structural and optoelectronic properties of quasi-1D hybrid 3-halogenopyridinium lead bromides

The present work focuses on the synthesis and structural, electronic, and optical properties of pyridinium lead bromides with halogen substituents in the meta position of the pyridine ring. All the compounds crystallize isotypically (spatial symmetry P2₁/c; four formula units in a unit cell). This makes the comparison of their properties straightforward. Both theoretical and experimental studies demonstrate the dependence of bandgap energies on the type of halogen substituent in the pyridinium ring due to an alteration of the crystallographic a-axis. Another effect caused by the type of halogen substituent on the electronic structure of the materials is the alteration of the valence band maxima positions and blue shift of the photoluminescence excitation maxima originating from the contribution of the iodine states into the valence band and the overlapping of the conduction band states with π* orbitals of organic cations, respectively. The observed room-temperature photoluminescence of the synthesized materials demonstrates their principal applicability to optoelectronics.