Perspectives in Dye Chemistry: A Rational Approach toward Functional Materials by Understanding the Aggregate State

Abstract

The past 20 years have witnessed a renaissance of dye chemistry, moving from traditional colorant research toward functional materials. Different from traditional colorant research, the properties of functional materials are governed extensively by intermolecular interactions, thereby entailing significant limitations to the classical approach based on molecular structure− molecular property (color, emission, redox properties, etc.) relationships for the respective dye molecules. However, as discussed in this Perspective, such an approach can be pursued for dye aggregates, and in many cases already well-tailored dimers are sufficient to understand the influence of supramolecular organization on the functional properties of ground and photoexcited states. Illustrative examples will be given for exciton coupling and charge-transfer coupling and how these properties relate to desirable functions such as fluorescence, symmetry-breaking charge separation, and singlet fission in molecular aggregates. While the progress in this research so far mostly originated from studies on well-defined folded and self-assembled structures composed of only two dye molecules, future work will have to advance toward larger oligomers of specific size and geometry. Furthermore, future experimental studies should be guided to a larger extent by theoretical predictions that may be supported by machine learning algorithms and new concepts from artificial intelligence. Beyond already pursued calculations of potential energy landscapes, we suggest the development of theoretical approaches that identify the most desirable dye aggregate structures for a particular property on functional energy landscapes.

Unusual Zig-Zag Effect in the Electrochemical Oxidation of Phenyl End-Capped α-Oligothiophenes

“…Such concepts are currently also applied to create organic biradicals 36 that are of interest for functional materials for singlet fission. 37,38…”

Two-step anti-cooperative self-assembly process into defined π-stacked dye oligomers: insights into aggregation-induced enhanced emission

“…Therefore, predicting and controlling the intermolecular arrangement along with understanding structure -property relationships, is a key step toward tailor-made functional organic materials. 2,3 For this, defined dye aggregates in solution can play an important role as model systems of reduced complexity. Already by investigating rather simple dimer systems, fundamental insights can be gained on processes like aggregationinduced emission 4 , symmetry-breaking charge separation 5 or singlet fission 6 .…”

Folding and fluorescence enhancement with strong odd–even effect for a series of merocyanine dye oligomers

“…5,6 In order to gain fundamental understanding of the intermolecular interactions leading to the desired functional properties, well-dened aggregates with precise control of the chromophore arrangement and aggregate size are desired. [7][8][9] The importance of dened chromophore arrangements is also demonstrated by natural light-harvesting complexes, in which photosynthetic pigments are organized into discrete structures stabilized by a protein shell, which ensures an efficient light-harvesting process and charge separation. 10,11 However, it is obvious that the realization of such complex structures is beyond the scope of current supramolecular chemistry.…”