Synthesis and Photophysical Properties of Glass-Forming Bay-Substituted Perylenediimide Derivatives

Abstract

A series of perylenediimide-based small molecules (PDI1-PDI5) containing electron-deficient groups in the bay region were synthesized and characterized. The PDI derivatives were found to be capable of forming molecular glasses with glass transition temperatures ranging from 50 to 102 degrees C. Detailed investigations of the optical properties of the synthesized derivatives were performed and compared with those obtained from quantum chemical calculations. Optimized molecular structures of the PDI derivatives exhibited core-twisting by 16 degrees and torsional angle between the bay substituent and the perylene core in the range of 60-72 degrees. The PDI derivatives exhibited absorption maxima in the range of 2.27-2.36 eV and emission maxima in the range of 2.10-2.28 eV. The impact of the bay substituents on the emission, fluorescence quantum yield, and lifetimes in solutions and thin films was established. The red shift of emission maxima (from 2.282 to 2.095 eV) observed for various PDIs in solutions was accompanied by significant reduction in the emission quantum yield (from 0.73 to 0.44) and corresponding increase of the fluorescence lifetime (from 4.5 to 6.8 ns). This was in agreement with quantum chemical calculations indicating decrease of the radiative relaxation rate due to reduction of the oscillator strength and remarkable decrease of the torsional activation barrier. The spectral properties of the wet-casted perylenediimide films featuring different bay substituents were also studied. The variation in the emission peak (of 0.25 eV) and the considerable increase of the Stokes shift (of 0.4 eV) are explained in terms of the formation of the amorphous state. The influence of the bay substituents on the thermal and spectral properties of the films are discussed.

Ultrafast photodriven intramolecular electron transfer from an iridium-based water-oxidation catalyst to perylene diimide derivatives

“…The solubility of the ligands and their respective metal complexes are comparable: 1 and 3 are very soluble in toluene, CH 2 Cl 2 , and benzonitrile, but they are less soluble in butyronitrile and only 3 is soluble in acetonitrile, and in these two latter solvents the UV-Vis spectra show evidence of PDI aggregation (28,29). Dyad 2 and ligand 4 are soluble in the entire range of solvents, as a result of the 3-pentyl tail at the imide that hinders π-π stacking of PDI aromatic cores (30) and the direct attachment of the phenyl side-groups, which may cause even greater distortion of the PDI core from planarity relative to the phenoxy-substituted dyes (31,32).…”

How does the interplay between bromine substitution at bay area and bulky substituents at imide position influence the photophysical properties of perylene diimides?

“…The geometries ( Fig. S5 †) of the compounds 2 and 4 were optimized by adopting B3LYP method with 6-31G** basic set 36,37 via energy minimization. The twist angles between the two naphthalenoid moieties of 2 and 4 are 22.11 and 21.83 respectively, which are close to the reported value in literature.…”

Synthesis, characterization and photovoltaic performance of novel glass-forming perylenediimide derivatives

“…An alternative approach consists in designing PDI derivatives (or electron acceptor materials in general) that form thin films that remain amorphous. 26,27 While amorphous solids possess no long-range periodical order, intermolecular interactions, such as the -stacking of aromatic moieties, can nonetheless be present and regulate to a certain degree the organization at the molecular level, with a continuous material that is exempt of grain boundaries. As with the majority of small molecules, most PDI derivatives readily crystallize.…”

“…As with the majority of small molecules, most PDI derivatives readily crystallize. 26,27 However, it was demonstrated that strategic molecular design can hinder the process of crystallization, resulting in molecular materials that can remain in the amorphous state for extended (sometimes indefinite) periods of time. This class of materials are known as molecular glasses, or amorphous molecular materials, and combine the monodisperse nature of small molecules with the processability of polymers.…”