Photophysics of perylene diimides in solutions and self-assembled films

Abstract

New perylene diimide based dendrimers were synthesized by the divergent synthetic method. Diamines with different lengths and methyl acrylate (or t-butyl acrylate) were used as the extension regents for the dendrimer growth steps. The photophysics of these synthesized PDIs was investigated with and without adding TFA. Intramolecular fluorescence quenching was observed by comparing the fluorescence intensity and lifetime before and after adding TFA, demonstrating a stronger quenching process for those PDIs having 2 or 3 carbons between the two nitrogens of the diamines. A 6 or 7 member ring mechanism for intramolecular electron transfer was presented. Photophysics of new water soluble perylene diimide, anionic n-PDI, CAS [694438-88-5] and cationic p-PDI, CAS [817207-4-7], was investigated in different media. The absorption spectra and quantum yield were modified by the presence of these reagents in a manner that suggests that weakly interacting complexes (such as H- or Jaggregates) are present in pure water and that complex formation can be enhanced by vii adding NaCl and polyelectrolytes or diminished by interacting with surfactants such as SDS and DTAC. A molecular layer-by-layer (MLBL) deposition process has been carried out for n-PDI and p-PDI through the strong π−π and electrostatic interactions. The fluorescence of these films shows an alternation of intensity according to which perylene species is on the outer layer, which is interpreted as the effect of facile energy transfer between the perylenes. Energy transfer in these films was also characterized by studying fluorescence quenching produced by the deposition of a single energy trapping layer (n-TDI, CAS[862852-56-0]). The MLBL technique can be utilized for other multiply-charged water soluble conjugated dye molecules such as n-PSA (CAS[59572-10-0]) and n-TDI, thereby demonstrating considerable potential for making organic semiconductor films. Polyelectrolyte films containing n-PDI and p-PDI were prepared from PSS and PDAC using the layer-by-layer (LBL) methodology. The optical density and fluorescence intensity of the LBL films grows linearly with the number of layers and we do not observe extraction of the PDI by subsequent polyelectrolyte deposition in the presence of 0.5M NaCl. The PDI fluorescence is substantially quenched in these films which we interpret as a self-quenching effect, enhanced by inter- and intra-layer energy transfer.