Clusterization-Triggered Emission Enhanced by Energy Transfer in the Layered Metal Halide Hybrid Material...

Clusterization-triggered emission (CTE) of nonconventional chromophores has recently attracted increased interest for its synergetic photophysical properties and promising applications, such as optical anticounterfeiting, white-light emission devices, or molecular sensing. Many studies have been conducted on pure organic clusteroluminogens (CLgens), but very few have explored organic-inorganic hybrid (OIH) materials. This work deals with optical properties of a new OIH compound (TET)₂[Pb₄Cl₁₆] (TET = N,N'-bis(2-aminoethyl)-1,3-propanediamine (C₇N₄H₂₄)), which presents an unprecedented two-dimensional perovskitoid structure formed by strongly distorted [Pb₄Cl₁₆] layers of corner and edge-sharing [PbCl₆] octahedra, separated by TET tetra-ammonium cations. Under UV-visible excitations, (TET)₂[Pb₄Cl₁₆] exhibits white-light emission, tunable excitation-wavelength-dependent emission, and green afterglow room temperature phosphorescence (RTP) lasting for more than 0.63 s, all of which are direct signatures of CTE. The optical interpretations are supported by density functional theory (DFT) calculations of the band structure. Two mechanisms are involved in the emission process: resonant energy transfer (RET) between the organic and the inorganic components, and clusteroluminescence (CL) governed by a rigid conformation of the organic cations and extended electron delocalization over supramolecular organic clusters confined within the interlayer spacing. The different features of CLgens in (TET)₂[Pb₄Cl₁₆] are discussed, and the role of the organic nonconjugated molecule in the emission process is emphasized.