Narrow-Bandgap Zero-Dimensional Chiral Hybrid Perovskites

Chiral hybrid perovskites (CHPs) are highly promising for next-generation chiroptoelectronics and spintronics. However, the incorporation of bulky organic chiral groups to impart chirality inevitably reduces structural dimensionality, leading to pronounced bandgap widening, which fundamentally limits their applications in narrow-bandgap optoelectronic devices. Here, for the first time, we report the construction of a pair of narrow-bandgap zero-dimensional (0D) CHPs, (R/S-MBA)2PtI6 (MBA = methylbenzylammonium), rationally designed by incorporating a 5d transition metal, Pt(IV), with energetically accessible 5d orbitals, in a chiral hybrid structure. The materials exhibit a small band gap of 1.27 eV, among the lowest values reported to date for intrinsic chiral systems. (R/S-MBA)2PtI6 adopts a unique 0D structure with quasi-layered packing, in which the terminal ammonium groups of the chiral cations are uniformly embedded within the inorganic sublayer, forming an extended hydrogen-bonding network. Electronic structure calculations reveal that the I(p) orbitals and their hybridization with Pt(d) orbitals define the band-edge states, while hydrogen bonding further tunes the electronic energy levels through local octahedral distortion and lone pair stabilization. The intrinsic integration of such a narrow bandgap with chiroptical activity endows the materials with broadband photoresponse and high polarization selectivity (g = 0.26). Notably, it also shows sensitive X-ray response with a sensitivity of 1410.8 μC Gy1- cm-2 and a low detection limit of 426.7 nGy s-1. These findings demonstrate that hydrogen-bonding-regulated 5d orbital-energy alignment provides an effective strategy to overcome the conventional trade-off between chirality-induced structural dimensionality reduction and bandgap widening in CHPs.