CONTENTS 1. Introduction 962 1.1. Prologue 962 1.2. Parent Perylene Bisimide Chromophore 963 1.3. Core-Substituted Perylene Bisimides 964 1.4. Perylene Bisimides in the Solid State 966 1.5. Areas of Application 966 2. Linear, Dendritic, and Macrocyclic Covalent PBI Ensembles 968 2.1. Excitonic Coupling and Deactivation Processes of Photoexcited PBIs 969 2.2. Rigid PBI Dimers 971 2.3. Flexible PBI Ensembles 974 2.4. Cyclic PBI Ensembles 976 3. π-Stacked PBI Assemblies 979 3.1. Self-Assembly of Core-Unsubstituted PBIs in Solution 979 3.2. Organization of Core-Unsubstituted PBIs in the Bulk Solid State 984 3.3. Self-Assembly of Amphiphilic PBIs in Aqueous Media and Solid Bulk State 987 3.4. Self-Assembly of Core-Substituted PBIs 991 3.5. Self-Assembly of Dye Arrays Composed of Multiple PBIs 995 3.6. Self-Assembly of Multichromophoric PBI Conjugates Containing Other Dyes 996 4. Hydrogen-Bond Directed Self-Assembly 1000 4.1. Self-Assembly Directed by Imide−Imide H-Bonding Interactions 1000 4.2. Self-Assembly Directed by Side-Chain Amide−Amide H-Bonding Interactions 1003 4.3. Self-Assembly Directed by Other H-Bonding Interactions 1006 4.4. Coassembly Directed by Imide−Melamine H-Bonding Interactions 1008 4.5. Coassembly Directed by Melamine−Cyanurate/Barbiturate H-Bonding Interactions 1011

A series of six perylene bisimides (PBIs) with hydrophilic and hydrophobic side chains at the imide nitrogens were applied for a comparative study of the solvent and structural effects on the aggregation behaviour of this class of dyes. A comparison of the binding constants in tetrachloromethane at room temperature revealed the highest binding constant of about 10(5) M(-1) for a PBI bearing 3,4,5-tridodecyloxyphenyl substituents at the imide nitrogens, followed by 3,4,5-tridodecylphenyl and alkyl-substituted PBIs, whereas no aggregation could be observed in the accessible concentration range for PBIs equipped with bulky 2,6-diisopropylphenyl substituents at the imide nitrogens. The aggregation behaviour of three properly soluble compounds was investigated in 17 different solvents covering a broad polarity range from nonpolar n-hexane to highly polar DMSO and water. Linear free energy relationships (LFER) revealed a biphasic behaviour between Gibbs free energies of aggregation and common empirical solvent polarity scales indicating particularly strong π-π stacking interactions in nonpolar aliphatic and polar alcoholic solvents whilst the weakest binding is observed in dichloromethane and chloroform. Accordingly, PBI aggregation is dominated by electrostatic interactions in nonpolar solvents and by solvophobic interactions in protic solvents. In water, the aggregation constant is increased far beyond LFER expectations pointing at a pronounced hydrophobic effect.

Ever since the discovery of dye self-assemblies in nature, there have been tremendous efforts to exploit biomimetic supramolecular assemblies for tailored artificial photon processing materials. This feature necessarily has resulted in an increasing demand for understanding exciton dynamics in the dye self-assemblies. In a sharp contrast with J-type aggregates, however, the detailed observation of exciton dynamics in H-type aggregates has remained challenging. In this study, as we succeed in measuring transient fluorescence from Frenkel state of π-stacked perylene tetracarboxylic acid bisimide dimer and oligomer aggregates, we present an experimental demonstration on Frenkel exciton dynamics of archetypal columnar π–π stacks of dyes. The analysis of the vibronic peak ratio of the transient fluorescence spectra reveals that unlike the simple π-stacked dimer, the photoexcitation energy in the columnar π-stacked oligomer aggregates is initially delocalized over at least three molecular units and moves coherently along the chain in tens of femtoseconds, preceding excimer formation process.

We have elucidated excimer-mediated intramolecular electron transfer in cofacially stacked PBIs tethered by two phenylene-butadiynylene loops. The electron transfer between energetically equivalent PBIs is revealed by the simultaneous observation of the PBI radical anion and cation bands in the transient absorption spectra. The fluorescence decay time of the excimer states is in good agreement with the rise time of PBI radical bands in transient absorption spectra suggesting that the electron transfer dynamics proceed via the excimer state. We can conclude that the excimer state effectuates the efficient charge transfer in the cofacially stacked PBI dimer.

A lucky chance: An unexpected halogen effect afforded novel squaraine‐based bright near‐infrared (NIR) fluorophores with nearly total transparency in the visible region and bright emission in the NIR region beyond 900 nm (see picture).