The response of electronic and energetic properties of conjugated vs aromatic molecules to an external uniform electric field

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.

Geometrical, electrical, and energetic parameters of hetero-disubstituted cumulenes and polyynes in the presence and absence of the external electric field

Cumulenes and polyynes have the potential to be applied as linear, sp-hybridized, one-dimensional all-carbon nanowires in molecular electronics and optoelectronics. The delocalization and conductivity descriptors of the two π-conjugated systems, heterodisubstituted with the NO2, CN, NH2, and OH groups, were studied using the B3LYP, B3LYP/D3, CAM-B3LYP, and ωB97XD DFT functionals, combined with the aug-cc-pVTZ basis set. Three independent types of molecular descriptors, based on geometry (the HOMA index), electrical properties (trace of the polarizability tensor), and energetic (the HOMO-LUMO energy gap) were shown to be mutually correlated and provided concordant indication that communication through the cumulene chain was considerably better than through the polyyne one. The communication can be tuned by using substituents of significantly different π-electron donor-acceptor properties as well as by the external electric field directed along the carbon chain.

Oriented External Electric Field Tuning of Unsubstituted Azoheteroarene Thermal Isomerization Half-Lives

Azoheteroarenes are relatively new photoswitchable compounds, where one of the phenyl rings of an azobenzene molecule is replaced by a heteroaromatic five-membered ring. Recent findings on methylated azoheteroarenes show that these photoswitches have potential in various optically addressable applications. The thermal stability of molecular switches is one of the primary factors considered in the design process. For molecular memory or energy storage devices, long thermal relaxation times are required. However, inducing a short thermal isomerization lifetime is required to release stored energy or as an alternative to photoswitching to avoid overlapping absorption spectra that reduce switching fidelity. In this study, we investigate how oriented external electric fields can be used to tune the thermal isomerization properties of three unsubstituted heteroaryl azo compounds-azoimidazole, azopyrazole, and azopyrrole. We show that favorable electric field orientations can increase the thermal half-life of studied molecules by as much as 60 times or reduce it from tens of days to seconds, compared to their half-life values in the field-free environment. A deeper understanding of the relationship between structure and kinetic properties provides insight as to how molecular switches can be designed for their electric field response in switching applications.