Cooperative enhancement of the nonlinear optical response in conjugated energetic materials: A TD-DFT study

Exploration for the Optical Properties and Fluorescent Prediction of Nitrotriazole and Nitrofurazan: First-Principles and TD-DFT Calculations

High-energy materials containing azole and furazan have revealed numerous properties; however, the underlying optical properties need to be solved. Meanwhile, the uncertainty for the choice of fluorescent matrix materials and the flexible situational conditions prompted us to estimate the optical and fluorescent properties of 5,5'-dinitro-2H,2H'-3,3'-bi-1,2,4-triazole (DNBT), 4,4'-dinitroazolefurazan (DNAF), and 4,4'-dinitro-3,3'-4,3'-ter-1,2,5-oxadiazole (DNTO). The first-principles calculation with improved dispersion correction terms and time-dependent density functional theory were utilized to calculate the absorbance and excitation energy of DNBT, DNAF, and DNTO, as well as characterization for their crystal structure, electronic structure, molecular orbitals, and so forth, synchronously. In this work, the absorbance anisotropy of DNBT and DNTO is stronger than that of DNAF. The absorbance for each of the (0,0,1) crystal planes in the three compounds is greater than that of the other two crystal planes. Moreover, DNBT has the maximum absorbance on the (0,0,1) crystal plane. The N-N-H from DNBT and N-O-N from DNTO and DNAF are responsible for these results, while N=N in DNAF weakens the performance of N-O-N. UV-vis spectra show that the maximum absorption wavelengths λ_max for DNBT, DNAF, and DNTO are 225, 228, and 201 nm, respectively. The number of five-membered rings and the coplanarity of groups in the intermolecular non-conjugation interaction potentially improve this ability due to the results from the crystal diffraction analysis. In addition, the polarization rate DNBT > DNTO > DNAF based on the molecular orbital analysis and the electrostatic potential calculation implies that the excitation energy of DNBT is less than DNTO, and the excitation energy of DNTO is less than DNAF. This work is beneficial to the expansion of energetic materials into the optical field and the accelerated application process of the related industry.

Theoretical study on functionalized acrylonitrile compounds with a large second-order nonlinear optical response

The nonlinear optical properties of the studied compounds were studied with the help of DFT calculations.

Electronic structure and second-order nonlinear optical property of chiral peropyrenes

Discovery of novel materials with excellent second-order nonlinear optical (NLO) properties is a very attractive topic in chemistry and materials science. Recently, much more attention has been paid to chiral compounds due to their inherent asymmetric structure and intramolecular charge transfer. Currently, the density functional theory (DFT) has become a powerful methodology to rationalize experimental observations and to design new materials with desirable properties. In this work, on the basis of the reported chiral peropyrene, we designed another five compounds consisting of donor or acceptor moieties and the donor/acceptor combinations. We systematically studied their geometrical/electronic structures and electronic transition/second-order NLO properties. The measured UV-Vis/CD spectra of compound 1 are almost reproduced by our calculations, enabling us to assign its electronic transition property and absolute configuration. For these compounds, the different substituents have great effect on their photophysical properties (i.e., band gap, absorption wavelength, and NLO response). The charge transfer synergy provides some useful information for further performance improvement. Interestingly, compound 6 shows a remarkably large first hyperpolarizability value of 18.14 × 10^-30 esu. Our research enables an opportunity for understanding the structure-property relationship of chiral peropyrenes. Graphical abstract The nonlinear optical properties of the studied compounds were studied with the aid of the DFT calculations.

TD-DFT calculations of one- and two-photon absorption in Coumarin C153 and Prodan: attuning theory to experiment

We use TD-DFT to calculate the one-photon absorption (1PA) and two-photon absorption (2PA) properties of C153 and Prodan in toluene and DMSO, and benchmark different methods relative to accurate experimental data available from the literature on these particular systems. As the first step, we modify the range-separated TD-DFT to provide the best prediction for the peak 1PA wavelength, and then apply the optimized functionals to achieve quantitative predictions of the corresponding two-photon absorption cross section, σ_2PA, with an accuracy ∼10-20% in C153 and ∼20-30% in Prodan. To elucidate the origin of residual discrepancies between the theory and experimental observations, we invoked the two essential states model for σ_2PA, which allows us to verify not only the transition wavelength and the σ_2PA value, but also to quantitatively benchmark the calculation of key molecular parameters such as the transition dipole moment and the change of the permanent dipole moment. Such comprehensive cross-checking indicates that a larger discrepancy in Prodan is most likely caused by a noted failure of DFT to predict the relative intensity and relative ordering of closely lying excited states with different degrees of intramolecular charge transfer, which we further support by analyzing the predictions obtained by high-level coupled-cluster calculations in the gas phase. Our results highlight the utility of benchmarking the calculations not only relative to other theoretical methods, but also in comparison to the experimental measurements, wherever such data are available.