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Two dimeric smectic molecules, namely α - ω -bis (4- n -pentylanilinebenzylidene-4′-oxy) butane (PABO4) and α - ω -bis (4- n -pentylanilinebenzylidene-4′-oxy) pentane (PABO5), have been considered for sensing UV light. The compounds’ optimization process has been performed through B3LYP hybrid functional together with basis set 6-31+G (d) using the input parameters from the crystallographer. The absorption of UV analysis of these compounds has been estimated, and the configuration interaction single-level method has been used to analyse the electronic transition features coupled with the calculation of excited states using semi-empirical Hamiltonian ZINDO. The CNDO/S, INDO/S together with CI approaches, has been utilized for comparative evaluation. The spectral-associated parameters have been summarized. The molecules discussed in this manuscript present several features, viz. the absorption range of the molecules that is sensitive to different wavelengths, the usage in flexible devices, offering the prospect for UV sensors. Further, the switching applications have been explored based on the oscillator strength data in various regions of wavelengths. Graphical abstract

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Theoretical analysis has been presented on a nematogen 4-dimethylaminobenzaldehyde (4-cyanophenylethylidene) hydrazone (E,E) (C18H18N4) to analyze its phase stability. The net atomic charges and dipole moment at each atomic centre has been calculated using complete neglect of differential overlap/spectroscopy method. The modified Rayleigh-Schrödinger perturbation theory along with multicentered-multipole expansion method has been used to evaluate the long-range intermolecular interactions. A "6-exp" potential function has been used for short-range interactions. The total interaction energy values have been used as input to calculate the probability of a particular configuration using the Maxwell-Boltzmann formula. Further, the Helmholtz free energy, and entropy at room temperature (300 K), nematic-isotropic transition temperature (436 K) and above transition temperature (500 K) have been computed. An attempt has been made to understand the phase stability and behaviour of the molecule. UV absorption spectra have been calculated using complete neglect of differential overlap/spectroscopy, and intermediate neglect of differential overlap/spectroscopy methods. The observed π → π * transitions, electrochemical properties based on highest occupied molecular orbital, lowest unoccupied molecular orbital energies, and principal polarizability components, and anisotropy of polarizability have been reported to understand the kinetic stability, global reactivity, and non-linear optical activity of the molecule.

In this paper the optimization of ofpara-azoxyanisole (PAA) has been carried outwith the help of density functional theory, B3LYP functional and 6-31+G (d) basis set. The input geometry taken was crystallographic in nature. AM1 method was used to evaluate the dipole moment and atomic net charge at different atomic centres. The modified Rayleigh-Schrodinger perturbation theory was used to estimate the long-range intermolecular interactions with the help of multicentered-multipole expansion method. For short-range interactions, a potential function of '6-exp' has been considered. Next, Helmholtz free energy and configurational entropy have been calculated. Theinteraction energy values corresponding to orientationaland translational motions at room temperature (300K) and nematic-isotropic transition temperature (408K) during different molecular interaction modes has been used for such a calculation. These parameters have been used to analyze the thermodynamic stability of PAA. The absorption wavelengths of the molecule have been estimated in the Ultraviolet visible region by employing Discrete Fourier Transform (DFT). UV-Vis stability of the molecule has also been discussed.

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