Cluster-model DFT simulations of the infrared spectra of triazine-based molecular crystals

Abstract

Understanding the intermolecular interactions in the context of crystal packing is of fundamental significance in molecular materials science. Infrared (IR) spectroscopy can provide complementary structural information; however, it still remains a great challenge to accurately predict the molecular IR vibrations in the crystalline phase. Here we report a cluster-model approach to simulate the IR spectra of triazine-based molecular crystals via density functional theory (DFT) calculations. In the properly designed cluster models, the molecular IR vibrations are expressed by a representative unit, while the nearest-neighbouring molecules are treated as a "frozen shell" to mimic the surrounding crystallographic environments. Much smaller clusters can be built by considering the crystallographic equivalence in the unit cell, which are able to perform DFT calculations on more complicated crystal structures with endurable computational costs. The simulated spectra show excellent consistencies with the experimental ones, particularly providing an in-depth understanding of the vibrational modes closely related to hydrogen bonding. Most importantly, the selectively built clusters based on the crystallographically independent molecules in the unit cell allow us to perform specific IR-spectral simulations, by which their distinct hydrogen-bonding environments have been clearly revealed for the first time.

Synthesis of carbon nitride oligomer as a precursor of melon with improved fluorescence quantum yield

“…Melon could be obtained by heating melamine in N 2 atmosphere at a relatively high temperature of 430-600 °C. The XRD and FT-IR data of melem and melon are in good agreement with the previously reported data, 13,[18][19][20][21][22] indicating that the compounds are successfully synthesized. The theoretical pressure phase diagrams of these CN compounds obtained by free-energy calculations 23 are consistent with the conditions described here for the synthesis of melem and melon.…”

“…Based on the FT-IR data, the NH stretching vibration peaks ((N-H)) observed at approximately 3500 cm -1 in the spectrum of melem 20 indicate the presence of NH 2 groups in melem, and identical peaks are also observed in the data for as-CN415.…”

Tune the Fluorescence and Electrochemiluminescence of Graphitic Carbon Nitride Nanosheets by Controlling the Defect States

“…Figure 1 shows the XRD patterns of those CNNSs. CNNSs 450 exhibits a typical peak of g‐CN (002) at 27.2° and a serial of peaks of melem [25–27] . When the condensation temperature is higher than 500 °C, the peaks of melem disappears completely in the obtained CNNSs.…”

“…CNNSs 450 exhibits a typical peak of g-CN (002) at 27.2°and a serial of peaks of melem. [25][26][27] When the condensation temperature is higher than 500°C, the peaks of melem disappears completely in the obtained CNNSs. Instead, only two typical diffractions peaks of g-CN appear, namely a peak at around 12.8°assigning to the hydrogen bonds for maintaining an intralayer long-range atomic order and a peak at around 27.5°assigning to the stacking of polymeric sheets.…”

DFT Modelling of Molecular Structure, Vibrational and UV-Vis Absorption Spectra of T-2 Toxin and 3-Deacetylcalonectrin

“…Previous molecular crystal studies have evidenced that the frequencies of the intra-molecular vibrational modes weakly depend on the crystalline environment in the absence of strong inter-molecular interaction. This assumption is widely used in discussing the vibrational states of the molecular crystals [28][29][30][31].…”