Molecular structure induced aggregation effects on the photophysical properties of perylene diimide based multilayer thin films

Abstract

Two perylene diimides (PDI) were synthesized to enable the preparation of multilayer films through a layer-by-layer (LbL) assembly technique using copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC). Multilayer films were fabricated with Ph-PDI or Pro-PDI (aniline groups or propargyl groups at the diimide positions) as perylene layers and either 1,3,5-tris(azidomethyl)benzene (L1), 1,4-bis(azidomethyl)benzene (L2) or 4,4’-di- azido-2,2’-stilbenedisulfonic acid disodium salt (L3) as linker layers. As shown from UV-Visible absorption and fluorescence spectroscopic studies, among the three linkers, PDIs with L1 displayed linear growth properties and the highest fluorescence intensity. Multilayer films of Pro-PDI with L1 had higher relative fluorescent intensity than that of Ph-PDI. Specular X-ray Reflectivity (XRR) and DFT calculations exhibited a higher tilting angle structure with less density was formed for Pro-PDI multilayer films, indicating more H-type aggregates present for Ph-PDI multilayer films. The achievable tunability of PDIs aggregation and the corresponding fluorescence properties may be illuminating for fabrication of new light harvesting arrays.