An Alternative Strategy to Polymorph Recognition at Work: The Emblematic Case of Coronene

Abstract

We show that the development of highly accurate density functional theory calculations coupled to low-frequency Raman spectroscopy constitutes a valid method for polymorph characterization alternative/complementary to X-ray. The method is applied here to the temperature-induced, first-order phase transition of coronene, known for a long time, but has remained structurally uncharacterized due to crystal breaking during the process. The astonishing fidelity of the Raman calculated spectra to the experiments allows us to unambiguously identify the low-temperature phase with the β-coronene polymorph, recently reported as new and obtained in the presence of a magnetic field. We also suggest that additional measurements are needed to confirm that a magnetic field can actually drive the growth of a β-polymorph surviving indefinitely at ambient temperature.

Lattice vibrations ofγ- andβ-coronene from Raman microscopy and theory

“…Figure 3(a) shows Raman spectra recorded from a single γ-coronene crystal while reducing the temperature at a rate of 15 K/min. Between 300 K and 175 K two peaks labelled A and B are visible, as observed in previous Raman measurements [20,26]. At 163 K the crystal was observed to shatter.…”

Crystal alignment of surface stabilized polymorph in thioindigo films

“…After re-determining, by X-ray crystallography, the structure of the thioindigo polymorphs, here named α and β, we have interpreted and rationalized their polarized Raman spectra in the low frequency range with the aid of DFT (Density functional theory) calculations. Over this range, polymorphs can be quickly and efficiently discriminated by identifying their vibrational fingerprint [10][11][12][13][14], a tool of the utmost importance when dealing with films. By growing micro-and nanocrystals on surfaces, using solution methods such as drop casting and https://doi.org/10.1016/j.dyepig.2019.107847 Received 17 July 2019; Received in revised form 28 August 2019; Accepted 28 August 2019 the solution bar assisted meniscus shearing (BAMS) technique [15][16][17], we have investigated the polymorph selectivity of the substrate.…”

Rational Control of Charge Transfer Excitons Toward High‐Contrast Reversible Mechanoresponsive Luminescent Switching

“…Similarly, the C=C band of cocrystal NCT (Raman spectra) displays a bathochromic shift for NDI unit (Δ ν ≈9 cm −1 ) but a blue‐shift for Cor. species (Δ ν ≈2 cm −1 ), indicating the existence of charge transfer between Cor and NDI after co‐assembly . However, the C=O stretching vibrations of NDI exhibit a blue‐shift (IR: Δ ν ≈5 cm −1 ; Raman: Δ ν ≈2–6 cm −1 ), which can be attributed to the weakened hydrogen bonding (−C=O⋅⋅⋅H) in the co‐crystal with an elongating distance (2.623 Å between adjacent NDI and Cor., Figure d) compared with that in pure NDI (2.386 Å for NDI‐NDI; Supporting Information, Figure S8) .…”

“…species (Dn % 2cm À1 ), indicating the existence of charge transfer between Cor and NDI after co-assembly. [45,46] However,t he C=Os tretching vibrations of NDI exhibit ab lueshift (IR: Dn % 5cm À1 ;Raman: Dn % 2-6 cm À1 ), which can be attributed to the weakened hydrogen bonding (ÀC=O•••H) in the co-crystal with an elongating distance (2.623 between adjacent NDI and Cor.,F igure 2d)c ompared with that in pure NDI (2.386 for NDI-NDI;S upporting Information, Figure S8). [47] Notably,t his CT transition has induced as ignificant photophysical property.A sp resented in Figure 3b and g, the ternary cocrystal NCT displays an excited red luminescence (a broad peak appeared at ca.…”