Photoluminescence Behavior of Zero-Dimensional Manganese Halide Tetrahedra Embedded in Conjugated Organic Matrices

Zero-dimensional hybrid manganese
halides with the type-I band
alignment between the manganese halide tetrahedra and organic matrices
have attracted much attention as highly efficient narrow-band green
emitters. Herein we study the photoluminescence (PL) behavior of hybrid
manganese bromides with type-II band alignment, where the lowest unoccupied
molecular orbital (LUMO) level can be tuned by employing quaternary
phosphonium dications with different degrees of conjugation. For low-conjugated
organic matrices, the band alignment can shift from type II in the
ground state to type I in the excited state, which enables high photoluminescence
quantum yields. In contrast, for high-conjugated organic matrices,
the band alignment cannot convert to type I in the excited state because
the LUMO lies too low, and thus, the excited electrons are transferred
from the tetrahedra to the matrices, which leads to severe PL quenching.
Our results show the importance of the excited-state band alignment
for understanding the PL behavior of hybrid metal halide semiconductors.