Hybrid Charge-Transfer Semiconductors: (C 7 H 7 )SbI 4 , (C 7 H 7 )BiI 4 , and Their Halide Congeners

Hybrid metal halides yield highly desirable optoelectronic properties and offer significant opportunity due to their solution processability. This contribution reports a new series of hybrid semiconductors, (C H )MX (M = Bi , Sb ; X = Cl , Br , I ), that are composed of edge-sharing MX chains separated in space by π-stacked tropylium (C H ) cations; the inorganic chains resemble the connectivity of BiI . The Bi compounds have blue-shifted optical absorptions relative to the Sb compounds that span the visible and near-IR region. Consistent with observations, DFT calculations reveal that the conduction band is composed of the tropylium cation and valence band primarily the inorganic chain: a charge-transfer semiconductor. The band gaps for both Bi and Sb compounds decrease systematically as a function of increasing halide size. These compounds are a rare example of charge-transfer semiconductors that also exhibit efficient crystal packing of the organic cations, thus providing an opportunity to study how structural packing affects optoelectronic properties.