Five concomitant polymorphs of a green fluorescent protein chromophore (GFPc) analogue: understanding variations in photoluminescence with π-stacking interactions

Abstract

The synthetically modified green fluorescent protein chromophore analogue 3,4,5-trimethoxybenzylidene imidazolinone (1) yielded five polymorphs (I, II, III, IV, V) concomitantly irrespective of the solvent used for crystallization. The pentamorphic modification of 1 is solely due to the interplay of iso-energetic weak intermolecular interactions in molecular associations as well as the conformational flexibility offered by a C—C single bond, which connects the electron-deficient moiety imidazolinone with the electron-rich trimethoxybenzylidene group. A common structural feature observed in all the polymorphs is the formation of a `zero-dimensional' centrosymmetric dimeric unit through a short and linear C—H...O hydrogen bond engaging phenyl C—H and imidazolinone carbonyl oxygen. However, the networking of these dimeric units showed a subtle difference in all the polymorphs. The 2D isostructurality was observed between polymorphs I, II and III, while the other two polymorphs IV and V revealed only `zero-dimensional' isostructurality. The different fluorescence emissions of Form I (blue) and Forms II to V (yellow) were attributed to the differences in π-stacking interactions. It shows that one can modulate the photophysical properties of these smart materials by slightly altering their crystal structure. Such an approach will aid in developing new multi-colour organic fluorescent materials of varying crystal structures for live-cell imaging and fluorescent sensing applications.

Cocrystal Approach to Modulate the Photoluminescent Properties of a GFP Chromophore Analogue: Role of Halogen/Hydrogen Bonding in Achieving a Wide Range of Solid-State Fluorescence Emissions

“…We previously reported five concomitant polymorphs of a chromophore analogue of GFP, 3,4,5trimethoxy benzylidine imidazolinone (3,4,5-TIA), and correlated the variance in luminescence with crystal packing. 43 Out of five polymorphs, one showed blue emission, while the other four revealed yellow emission. This study reports the eight cocrystals of GFP (3,4,5-TIA) (A) with different cocrystal formers displaying a wide range of fluorescence emissions ranging from blue−yellow−dark orange.…”

“…The variations in photoluminescence were attributed to differences in the aggregation modes like H-aggregation and J-aggregation. We previously reported five concomitant polymorphs of a chromophore analogue of GFP, 3,4,5-trimethoxy benzylidine imidazolinone (3,4,5-TIA), and correlated the variance in luminescence with crystal packing . Out of five polymorphs, one showed blue emission, while the other four revealed yellow emission.…”

Locking the GFP Fluorophore to Enhance Its Emission Intensity

“…In the crystalline state, 5 can organize in five different polymorphs, all of them presenting AIEE properties with quantum yields of 0.02-0.05, due to the restriction of molecular motions. The emission wavelength is different between the polymorphs, varying from a blue emission around 450 nm to a yellow emission around 550nm, as a result of the strength of the π-π interactions between the donor and the acceptor units in the polymorphs [19]. In an attempt to rigidify the backbone of the dyes, large aromatic substituents were introduced in replacement of the p-hydroxyphenyl ring on the GFPc 6a-e (Figure 6) [20].…”

Polymorphs of Green Fluorescence Protein Chromophore Analogue: Fluorescence Switching with Thermal Stimuli

“…Previously, we reported the five concomitant polymorphs of the synthetically modified chromophore of green fluorescent protein (GFP), solely due to the interplay of isoenergetic weak intermolecular interactions in molecular aggregation. The different fluorescence emission in these polymorphs was attributed to the differences in π-stacking interactions . To continue our work on the generation of a novel class of color-tunable organic fluorescent materials by structural modification and supramolecular control, we have synthesized the GFPc analogue 3,4,5-trimethoxy benzylidine imidazolinone acetate ( 1 ) and investigated its polymorphic tendency under different crystallization conditions.…”

“…The different fluorescence emission in these polymorphs was attributed to the differences in π-stacking interactions. 26 To continue our work on the generation of a novel class of colortunable organic fluorescent materials by structural modification and supramolecular control, we have synthesized the GFPc analogue 3,4,5-trimethoxy benzylidine imidazolinone acetate (1) and investigated its polymorphic tendency under different crystallization conditions. Our investigations into the polymorph screening of 1 resulted in the formation of three polymorphs with different photoluminescence, two of which showed irreversible thermal fluorescent switching due to polymorphic phase transition.…”