Rationalization of the Color Properties of Fluorescein in the Solid State: A Combined Computational and Experimental Study

Abstract

Fluorescein is known to exist in three tautomeric forms defined as quinoid, zwitterionic, and lactoid. In the solid state, the quinoid and zwitterionic forms give rise to red and yellow materials, respectively. The lactoid form has not been crystallized pure, although its cocrystal and solvate forms exhibit colors ranging from yellow to green. An explanation for the observed colors of the crystals is found using a combination of UV/Vis spectroscopy and plane‐wave DFT calculations. The role of cocrystal coformers in modifying crystal color is also established. Several new crystal structures are determined using a combination of X‐ray and electron diffraction, solid‐state NMR spectroscopy, and crystal structure prediction (CSP). The protocol presented herein may be used to predict color properties of materials prior to their synthesis.

Experimental and Theoretical Evaluation of the Stability of True MOF Polymorphs Explains Their Mechanochemical Interconversions

“…It is interesting to note that the observed energy differences between ZIF polymorphs significantly exceed those between polymorphs of organic molecules, where lattice energy differences lie within 7.2 kJ mol -1 in 95% of cases. 63 In order to better understand materials structural features responsible for observed energetic trends, 64 we accompanied the calorimetric studies with CASTEP 56 periodic DFT calculations ( Table 2). In these calculations, the geometries of observed structures were fully optimized (atom coordinates and cell parameters) to yield total electronic energies.…”

Hypergolic Triggers as Co‐crystal Formers: Co‐crystallization for Creating New Hypergolic Materials with Tunable Energy Content

“…This value is consistent with the hypergolicity as well as the red color of the material. In contrast, solid 1 exhibits a higher measured band gap (3.40 eV), consistent with its colorless appearance . A lowering of the band gap upon co‐crystallization is explained by theoretical density of states (DOS) calculations (see Supporting Information), which reveal that the highest occupied crystal orbital (HOCO) of 1⋅NBz is entirely localized on the NBz molecules at each point in k space.…”

Energy–Structure–Function Maps: Cartography for Materials Discovery

“…In this application area, the use of solid‐state density functional theory (DFT) for assessing relative stabilities has gained popularity; the high cost of DFT can be justified when the computational effort is focused on the crystal packing of one target molecule. Applications of CSP to functional materials have been less common, at least for molecular crystals, aside from a relatively small number of studies for small‐molecule organic semiconductors, pigments, fluorescent molecules, and explosives . However, the development of efficient, accurate force fields, coupled with highly parallelized structure searching methods and rapid improvements in computational hardware mean that it is now possible to apply CSP in screening applications for the discovery of functional organic materials (Figure b) and to couple this with property predictions.…”