Phase Transition and Luminescent Property Change Induced by Different Organic Cations in One-Dimensional Double Perovskites

Double perovskites (DPs) have attracted attention in the field of luminescence due to their inherent broadband emission of self-trapping excitons. In this work, we choose [(CH₃)₃NCH₂CHCH₂]⁺ and [CH₃CHOHCH₂NH₂]⁺ as organic cations to synthesize two new organic-inorganic hybrid DPs, [(CH₃)₃NCH₂CHCH₂]₂KInCl₆ (1) and [CH₃CHOHCH₂NH₂]₂KInCl₆ (2). The [KCl₆]^3- and [InCl₆]^3- octahedra are interchangeably connected by sharing two opposite faces, forming a one-dimensional coordination chain. Each K atom coordinates with six chlorine atoms in 1, while it coordinates with two oxygen atoms in addition to the six chlorine atoms in 2. The coordination between ions K and O in compound 2 may have significantly reduced its luminescence. As a result, compound 1 shows bright-yellow light with a quantum yield of more than 90%, while 2 shows weak blue light with a quantum yield of only 0.98%. In addition, different from no phase transition found in 2, 1 undergoes a reversible phase transition at 324/307 K in the heating-cooling cycle. Through structural and spectral analysis and density functional theory calculation, we conclude that the larger degree of [InCl₆]^3- octahedral distortion and the larger anion distance (In···In) also cause the PLQY of compound 1 to be higher than that of compound 2.