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Roseolumiflavin is a deep red microcrystalline derivative of isoalloxazine that exhibits a weak photophysical activity in the solid state. In aqueous as well as in acidic solution of formic or acetic acid, respectively, it tends to form solvates. Herein, we present a set of binary and ternary roseolumiflavin solvates including one hydrate and a solvate hydrate. The impact of the solvent on solvate formation along with an in-depth structural analysis was investigated. Calculations of the lattice energies provide insight into the phase stability of the evaluated systems showing an energetic benefit for all solvates with values up to −395.82 kJ/mol. The total interaction energies between molecules calculated via Crystal Explorer further identified cofacial π···π stacks to be the most strongly bonding fragments in the crystal lattices for all systems except the formic acid solvate, followed by remarkably weaker hydrogen-bonded arrangements. The energetic contributions of single intermolecular interactions within the fragments are evaluated by an atoms-in-molecules approach. It is shown that physicochemical properties, such as thermal stability, can be tuned depending on the incorporated solvent molecules despite a high decomposition temperature of the chromophore. [ABSTRACT FROM AUTHOR]

A structural study on the solid, microcrystalline chromophore roseolumiflavin was carried out. Based on rational design considerations three binary co-crystals were prepared with a primary focus set on utilizing the imide functional group. Therefore, robust supramolecular synthons, including a carboxylic acid–amide dimer, halogen bonding, as well as a hydrogen-bonded three-point binding motif, were successfully incorporated into the multicomponent systems. All the co-crystals showed a blue-shifted fluorescence in the red range compared to the near-infrared-emitting solid roseolumiflavin. Solvatochromic studies finally elucidated that the degree of close packing between the flavin molecules within the crystal structures was decisive for the emission colour. These results render new possibilities to investigate flavins in the aspect of crystal engineering to tune optical properties of organic chromophores in the solid state. [ABSTRACT FROM AUTHOR]