@article { ISI:000272896300048,
	title = {Magnetic phase transition in valence tautomers as polymorphs of 3-iodolawsone: Single crystal X-ray structure, DSC and EPR studies},
	journal = {Journal of Molecular Structure},
	volume = {938},
	number = {1-3},
	year = {2009},
	month = {DEC},
	pages = {328-335},
	publisher = {ELSEVIER SCIENCE BV},
	address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS},
	abstract = {<p>Three polymorphs of 3-iodolawsone (I-III) have been isolated and characterized by single crystal X-ray diffraction, electron paramagnetic resonance (EPR) spectroscopy and differential scanning calorimetry (DSC) techniques. Polymorphs I and II were crystallized from methanol in two different valence tautomeric forms: hydroxynaphthoquinone (HNQ) and hydroxynaphthoseimquinone (HNSQ) as needles and thick plates, respectively. Polymorph III was crystallized from ethanol in HNQ form, as thin plates Chiral crystals of I belongs to the orthorhombic P2(1)2(1)2(1) space group: II and III belong to the monochnic non-centrosymmetric space group Cc. The molecules are packed via O-H O bonding and pi . pi stacking interactions. The study reveals that relatively stronger intermolecular H-bonding (2.02 angstrom) and most favoured pi . pi stacking (similar to 3 49 angstrom) interactions lead II to HNSQ radicals, presence of which was confirmed by EPR (g = 2.0052) spectroscopy. Interestingly, these materials exhibit crystal-to-crystal magnetic phase transition from polymorph I (diamagnetic) to polymorph II (paramagnetic structure) at 171.1 degrees C as identified by DSC and X-ray crystallographic studies (C) 2009 Elsevier B.V. All rights reserved</p>},
	keywords = {3-Iodolawsone, Hydroxynaphthoquinone (HNQ), Hydroxynaphthosemiquinone radical (HNSQ), Magnetic phase transition, Polymorphs, Valence tautomers},
	issn = {0022-2860},
	doi = {10.1016/j.molstruc.2009.10.005},
	author = {Zaware, Santosh B. and Dagade-Waghmode, Shobha and Gonnade, Rajesh G. and Srinivas, Darbha and Rane, Sandhya Y.}
}
@article {46689,
	title = {Five concomitant polymorphs of a green fluorescent protein chromophore (GFPc) analogue: understanding variations in photoluminescence with pi-stacking interactions},
	journal = {Acta Crystallographica Section B-Structural Science Crystal Engineering and Materials},
	volume = {76},
	year = {2020},
	month = {OCT},
	pages = {850-864},
	type = {Article},
	abstract = {<p>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 {\textquoteleft}zero-dimensional{\textquoteright} centrosymmetric dimeric unit through a short and linear C-H center dot center dot center dot 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 {\textquoteleft}zero-dimensional{\textquoteright} isostructurality. The different fluorescence emissions of Form I (blue) and Forms II to V (yellow) were attributed to the differences in pi-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.</p>
},
	keywords = {green fluorescent protein, hydrogen bonds, isostructurality, photoluminescence, pi-stacking, Polymorphs},
	doi = {10.1107/S2052520620010343},
	author = {Mali, Bhupendra P. and Dash, Soumya Ranjan and Nikam, Shrikant B. and Puthuvakkal, Anisha and Vanka, Kumar and Manoj, Kochunnoonny and Gonnade, Rajesh G.}
}
