Fluorescent J-Aggregates of Core-Substituted Perylene Bisimides: Studies on Structure−Property Relationship, Nucleation−Elongation Mechanism, and Sergeants-and-Soldiers Principle

Abstract

A series of highly soluble and fluorescent, at core tetraaryloxy-substituted and in imide positions hydrogen atom containing perylene bisimide (PBI) dyes 1a-e with varying peripheral side chains have been synthesized and thoroughly characterized. The self-assembly of these PBIs has been studied in detail by UV/vis, linear dichroism (LD) and circular dichroism (CD) spectroscopy, and scanning probe microscopy (AFM, STM). These studies revealed that the present PBIs self-assemble into extended double string cables, which consist of two hydrogen-bonded supramolecular polymeric chains of densely packed and strongly excitonically coupled PBI chromophores, providing highly fluorescent J-aggregates. The aggregation strength ("melting" temperature) and the fluorescence properties of these J-aggregates are dependent on the number and chain length of the peripheral alkoxy substituents, thus revealing a structure-property relationship. In contrast to previously reported assemblies of PBIs, for which the aggregation process is described by the isodesmic (or equal K) model, a cooperative nucleation-elongation mechanism applies for the aggregation of the present assemblies as revealed by concentration-dependent UV/vis absorption studies with the chiral PBI 1e, providing equilibrium constants for dimerization (= nucleation) of K(2) = 13 +/- 11 L mol(-1) and for elongation of K = 2.3 +/- 0.1 x 10(6) L mol(-1) in methylcyclohexane (MCH). LD spectroscopic measurements have been performed to analyze the orientation of the monomers within the aggregates. The nonlinearity of chiral amplification in PBI aggregates directed by sergeants-and-soldiers principle has been elucidated by coaggregation experiments of different PBI dyes using CD spectroscopy. The dimensions as well as the molecular arrangement of the monomeric units in assemblies have been explored by atomic force microscopy (AFM) and scanning tunneling microscopy (STM).

Exciton Transport in Molecular Aggregates – From Natural Antennas to Synthetic Chromophore Systems

“…Due to the much lower dimerization (= nucleation) constant (K 2 = 13 M −1 ) compared to the elongation constant (K = 2.3 × 10 6 M −1 ) an instantaneous fiber growth is observed for these molecules at a specific (concentration-and temperature-dependent) critical concentration. [286] This feature together with the high fluorescence quantum yield were essential for a series of single-molecule experiments that were carried out subsequently for PBI 7 J-aggregates.…”

“…Adapted with permission. [286] Copyright 2009, American Chemical Society and adapted with permission. [288] Copyright 2014, American Chemical Society.…”

Photophysical Properties of Perylenetetracarboxylic Diimide Dimers with Slipped “Face-to-Face” Stacked Structure and Different Bay Substitutions

“…The fluorescence lifetime increases slightly from 6.1 ns for the monomer 3 to 7.8 ns for dimer 8. The Stokes shift of the emission band is 36 nm, which is also significantly larger than that observed for the typical "J-type" aggregates [6]- [8]. All the characteristics of the emission of dimer 8 as mentioned above suggest that the 620 nm emission can be assigned to the "excimer-like" state of dimer 8.…”

“…Several J-type aggregates assembled from PDI based on non-covalent intermolecular interactions, such as hydrogen bonding and/or π − π stacking interaction, have been intensively studied [6]- [8]. However, these aggre-gates showed significant differences on photophysical properties.…”

Amplification of local chirality within a folded dendrimer. An intramolecular ‘sergeants and soldiers’ experiment

“…Correlated conformational changes are often linked to chiral amplification phenomenon in synthetic systems (Lockman et al 2005). Chiral amplification in these systems occurs via a 'sergeant and soldiers' mechanism (Green et al 1989) in which a small fraction of chiral subunits/monomers ('sergeants') transmits conformational information to achiral segments ('soldiers') of helical polymer chains, (for some reviews, see Green et al 1999Green et al , 2001Nakano & Okamoto 2001Fujiki 2008;Yashima & Maeda 2008) foldamers (Prince et al 2000;Dolain et al 2005;Maurizot et al 2005;Hou et al 2006;Kolomiets et al 2007;Cai et al 2008;Hu et al 2008;King et al 2008;Kohmoto et al 2008;Naidu et al 2009) or supramolecular assemblies (Engelkamp et al 1999;Ajayaghosh et al 2006;Mateos-Timoneda et al 2006;Nagai et al 2006;George et al 2007;Monti et al 2007;Hembury et al 2008;Lohr & Wuerthner 2008a,b;Praveen et al 2008;Kaiser et al 2009). Although 'sergeants and soldiers' chiral amplification has been achieved in dendritic assemblies (Palmans et al 1997; van Gestel et al 2005;Wilson et al 2006;Shao & Parquette 2008;Percec et al 2009), an intramolecular 'sergeants and soldiers' type chiral amplification remains an unrealized objective for dendrimeric systems.…”