Crystal structures of five imidazolin-5-ones are discussed. While molecules 1-3 show a donor-acceptor type of $\pi \cdots \pi$ lateral offset stacking, C-H$\cdots \pi$ interactions are found to play dominant roles in molecules 2 and 4. In molecule 2, C-H$\cdots \pi$ interactions further form lateral offset stack to form extended C-H$\cdots \pi \cdots \pi \cdots$H-C hydrogen bonds. Molecule 4, however shows a layer structure with interlayer C-H$\cdots \pi \cdots $H-C hydrogen bonds and interlayer stacking of imidazolin-5-one heterocycles. These structures show how weak $\pi \cdots \pi$ interactions can be exploited for tailoring supramolecular assemblies.

Crystal structures of four green fluorescent protein (GFP) chromophore analogues with different packing interactions could be tuned by appropriate substitutions around the imidazolin-5-one ring are reported here. Compound 1 was crystallized from tetrahydrofuran at room temperature while compounds 2-4 have been crystallized from a mixture of methanol and dichloromethane in 3:1 ratio. Molecule 1, 2 and 3 crystallized in monoclinic lattice while molecule 4 preferred to crystallize in a triclinic crystal system. The crystal packing of these molecules was stabilized by C-H$\ldots \pi$ stacking and C-H$\ldots $O type of supramolecular interactions. The results reveal that packing diversity can be easily accomplished in these molecules by tuning the substituents around the imidazolin-5-one ring. Photophysical studies also reveal that all have good quantum yield and fluoresce typically in red region due to presence of electron donating groups around the imidazolin-5-one ring.

Crystal structures of four red kaede fluorescence protein chromophore analogues are reported here. Molecules I-III adopt a non-planar geometry stabilized by 𝜋 …𝜋 stacking and hydrogen bonding. Introduction of an electron push-pull system induces molecule IV to be planar and a C = O…𝜋 supramolecular interaction is observed as well. Strong electron withdrawing and donating groups also ensure formation of a higher order two and three dimensional supramolecular architecture through hydrogen bonds in molecules I and IV. All the analogues exhibit good photoluminescence properties and emit in the red region with excellent quantum yields.

The imino nitrogen of p-methoxybenzylideneimidazolinone (pMBDI) was protonated using aqueous HClO4 and HCl acid and crystallized in monoclinic crystal system with P2₁/n space group. Interestingly, the protonated compounds are fluorescent in polar solvents but non-fluorescent in non-polar solvent as well as in the solid state. These results point to the existence of a non-radiative pathway involving the imidazole nitrogen in the quenching of excited states in these compounds.

We examine the effect of crown ether ring sizes on structure and properties of three terminally protected tripeptides containing substituted dehydrophenylalanine residues; Bz-∆Phe(12-crown-4)-Phe-Phe-OMe, Bz-∆Phe(15-crown-5)-Phe-Phe-OMe, Bz-∆Phe(18-crown-6)-Phe-Phe-OMe. The resultant self-assembly of the peptides generates nano-vesicles, which further alter into the necklace type of structures that were characterized via their SEM, LRTEM, and AFM images.We also report the disruption of these vesicles in the presence of different metal ions.