Role of chain length in the physical properties and hydrophobicity of (CnH2n+1NH3)2PbX4 (n = 6, 8, 10, 12, 14, and 16; X = Br and I) 2D metal halide perovskites

We report here the preparation and characterization of two families of RP 2D perovskites including linear monoammonium cations, namely (CnH2n+1NH3)2PbBr4 and (CnH2n+1NH3)2PbI4 with n = 4, 6, 8, 10, 12, 14 and 16. Their structural and optical properties show some similarities with, however, distinct features related to the presence of phase transitions occurring when different ligands are present. The optical properties confirm a general blue-shift for the (CnH2n+1NH3)2PbBr4 system with respect to the (CnH2n+1NH3)2PbI4 family with the PL data showing two distinct variation paths due to their excitonic emission behavior, one directly related to the chain length and another one depending on the ammonium coordination to the halogen atoms. The water stability of (CnH2n+1NH3)2PbBr4 and (CnH2n+1NH3)2PbI4 has been assessed and the results show an improved hydrophobicity upon increasing the number of carbon atoms of the alkyl chain as well as by moving from iodide to bromide perovskites.