DFT/TDDFT Investigation on donor-acceptor triazole-based copolymers for organic photovoltaics

Theoretical Insights into the Structural and Optical Properties of D-π-A-based Cyanostilbene Systems of α and β Variants

The π-conjugated organic molecules containing cyanostilbene motifs have been extensively investigated due to their great potential applications in several optoelectronic and biological fields. Developing efficient molecules in this respect requires strategic structural engineering and a deep understanding of the structure-property relationship at the molecular level. In this context, understanding the impact of positional isomerism in cyanostilbene systems is a fundamental aspect of designing desired materials with improved photophysical properties. Herein, we designed ten donor-π-acceptor (D-π-A) type cyanostilbene derivatives (P1 - P10) with different π linkers and compared their structural and optoelectronic properties arising from the positional variations of the -CN group (α and β- variations) through the utilization of density functional theory (DFT) and time-dependent DFT (TDDFT) methods. The topological analyses of the electron density are used to explain the relatively high stability of α isomer compared to that of β. Frontier molecular orbital analysis reveals that 17 molecules tend to show a reduced highest occupied molecular orbital-lowest unoccupied molecular orbital gap, and most of them showed a greater nonlinear optical (NLO) character compared to the parent molecule. TDDFT calculations indicate that β isomers show higher absorption maxima compared to their α counterparts. Among all the scrutinized molecules, the absorption maximum extended up to 602 nm for P9 and it possesses the highest first-order hyperpolarizability. This study sheds light on positional isomers and their reactivity, absorption spectra, and NLO properties of D-π-A type architecture that can be suitably tuned by appropriating the π-bridge for practical applications.

Experimental and Computational Approaches to Sulfonated Poly(arylene ether sulfone) Synthesis Using Different Halogen Atoms at the Reactive Site

Engineering thermoplastics, such as poly(arylene ether sulfone), are more often synthesized using F-containing monomers rather than Cl-containing monomers because the F atom is considered more electronegative than Cl, leading to a better condensation polymerization reaction. In this study, the reaction's spontaneity improved when Cl atoms were used compared to the case using F atoms. Specifically, sulfonated poly(arylene ether sulfone) was synthesized by reacting 4,4'-dihydroxybiphenyl with two types of biphenyl sulfone monomers containing Cl and F atoms. No significant difference was observed in the structural, elemental, and chemical properties of the two copolymers based on nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, transmission electron microscopy, and electrochemical impedance spectroscopy. However, the solution viscosity and mechanical strength of the copolymer synthesized with the Cl-terminal monomers were slightly higher than those of the copolymer synthesized with the F-terminal monomers due to higher reaction spontaneity. The first-principle study was employed to elucidate the underlying mechanisms of these reactions.