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

Abstract

Polymorphs of fluorescent organic materials offer significant implications in optoelectronics and advanced materials as they modulate photoluminescence properties. A slight alteration in the conformation/ packing of molecules in the crystals shows variation in photoluminescence. This necessitates the polymorph screening of these materials to develop novel crystalline forms with distinct fluorescence emissions for broader application. In continuation of our work on the polymorph screening of Green Fluorescence Protein Chromophore (GFPc), we have synthesized a new imidazoline derivative, ethyl (Z)-2-(2-methyl-5-oxo-4-(3,4,5-trimethoxybenzylidene)-4,5-dihydro-1H-imidazol-1-yl)acetate (1). Polymorph screening of 1 under different crystallization conditions revealed three polymorphs, Form I (needle), Form II (block), and Form III (polycrystalline material). Forms I and II are the outcome of solution crystallization, whereas Form III was produced from the melt crystallization of Forms I and II. DSC, HSM, and powder and single-crystal XRD studies indicate the conversion of Form I and Form III crystals to Form II crystals on thermal stimuli. The photoluminescence studies revealed cyan, yellow, and yellowish-green fluorescence emission for Forms I, II, and III crystals, respectively. The difference in photoluminescence could be due to the variance in aggregation modes like H-aggregation in Form I and J-aggregation in Form II crystals. Form I, Form II, and Form III crystals also showed irreversible thermal fluorescent switching from cyan-yellow-green due to polymorphic phase transitions. The study correlates the direct observation of the modulation of the excited-state transition under thermal stimuli in the crystalline phase. It will help augment the pace in the research of thermally responsive fluorescent materials.

Reversible human-temperature-responsive luminescence switching in a Mn(ii)-based metal halide

“…However, the thermal-response temperatures of previously reported thermosensitive materials are either below the refrigeration temperature or much higher than room temperature (RT). 16–18…”

“…However, the thermal-response temperatures of previously reported thermosensitive materials are either below the refrigeration temperature or much higher than room temperature (RT). [16][17][18] Recently, organic-inorganic hybrid metal halides (OIMHs) have emerged as a new class of stimuli-responsive luminescent materials, owing to the structural flexibility afforded by their modular structure of organic and metal-halide-cluster moieties. [19][20][21][22][23] Therefore, OIMHs can provide a rich database for exploring promising candidates to serve as thermally responsive luminescent materials.…”

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

“…The experimental PXRD studies were carried out on a D8 VENTURE (Bruker-AXS) singlecrystal X-ray diffractometer. 42 The ground powder sample of cocrystals of A was taken in a Lindeman capillary (0.7 mm diameter) and mounted on the diffractometer. The sample-to-detector distance was fixed at 230 mm, and the angles χ were set at 0°.…”

“…38−41 Recently, we reported the irreversible thermal fluorescence switching of polymorphs of a GFPc analogue from cyan−yellow−green due to phase transitions. 42 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, 3,4,5trimethoxy benzylidine imidazolinone (3,4,5-TIA), and correlated the variance in luminescence with crystal packing.…”

“…We followed the cocrystallization approach to produce novel solid crystalline materials of green fluorescent protein (GFP) chromophore analogues to widen the scope of these materials for an extensive range of fluorescence emissions. Especially, green fluorescent protein chromophore (GFPc) analogues are finding applications in molecular biology and biotechnology as genetically encoded fluorescent tags because of their excellent optical and electronic properties. − Recently, we reported the irreversible thermal fluorescence switching of polymorphs of a GFPc analogue from cyan–yellow–green due to phase transitions . The variations in photoluminescence were attributed to differences in the aggregation modes like H-aggregation and J-aggregation.…”