Yang Y, Wang Y, Xie Y, Xiong T, Yuan Z, Zhang Y, Qian S, Xiao Y. Fused perylenebisimide-carbazole: new ladder chromophores with enhanced third-order nonlinear optical activities. Chem Commun (Camb). 2011 Oct 14;47(38):10749–51. doi: 10.1039/c1cc14071j. PMID: 21870017.