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

• Published in: RSC advances Vol. 7; no. 26; pp. 16155 - 16162
• Main Authors: Shao, Yu, Zhang, Xinlin, Liang, Kai, Wang, Jing, Lin, Yuejian, Yang, Shuguang, Zhang, Wen-Bin, Zhu, Meifang, Sun, Bin
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 01.01.2017
• Subjects: Bromine; Chromophores; Comparative studies; Computer simulation; Crystallography; Crystals; Dimers; Electronic structure; Emission; Fluorescence; moieties; molecular dynamics; Molecular structure; Naphthalene; Optoelectronics; Polyhedral oligomeric silsesquioxane; Properties (attributes); Self-assembly; silsesquioxanes; Substitutes
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/c7ra00779e

This article reports a comparative study on the synthesis, self-assembly, and photophysical properties of perylene diimides (PDIs) symmetrically tethered with long alkyl chains or polyhedral oligomeric silsesquioxanes (POSS) at the imide position and/or bromo substitutions at 1,7-positions of the bay area. This series of samples include dodecyl-PDI H -dodecyl ( 1 ), dodecyl-PDI Br -dodecyl ( 2 ), POSS-PDI H -POSS ( 3 ), and POSS-PDI Br -POSS ( 4 ). In solution, the PDIs with bromine substitution at bay area ( 2 , 4 ) exhibit red-shifted absorption maximum compared to those without ( 1 , 3 ), which is consistent with a twisted perylene chromophore as revealed by molecular simulation. Similar bathochromatic shift was observed on the solid crystal state emission of 2 as compared to 1 . However, in crystals, the emission spectrum of 4 exhibits a seemingly hypochromatic shift relative to that of 3 , which could be rationalized by their packing in the crystals. The bromo substitution is believed to partially quench the fluorescence and the relatively loose packing of the twisted π-plane of 4 may not be able to confine π-plane in place, leaving multiple pathways for fluorescent quenching rather than red-shifted emission. While both 3 and 4 exhibit a unique dimer packing scheme, the dimers have quite different longitudinal offset and transverse offset of the π-plane. The longitudinal offset in dimers of 4 is so large that the naphthalene moieties in the dimer almost adopt a face-to-face arrangement and their mutual interactions are considered relatively independent. All these contribute to the less red-shifted fluorescent emission and the lower fluorescent yields in crystals of 4 relative to 3 as compared to that in solution. The study shall shed light into the complicated mutual interactions among intrinsic electronic structure, microscopic molecular packing, and the macroscopic optoelectronic properties. This article reports a comparative study on the photophysical properties of perylene diimides which caused by the interplay between bromine substitution at bay area and bulky substituents at imide position.