First-principles theoretical designing of planar non-fullerene small molecular acceptors for organic solar cells: manipulation of noncovalent interactions

Non-fullerene small molecular acceptors (NFSMAs) exhibit promising photovoltaic performance; however, their electron mobilities are still relatively lower than those of fullerene derivatives. The construction of a highly planar conjugated system is an important strategy to achieve high charge mobility. In chemical parlance, it is tedious and costly to synthesize planar compounds by restricting the rotation at a specific bond. Recently, nonbonding intramolecular interactions, also termed "conformational locks," have been considered as an alternative way to achieve planar geometry. The successful implementation of this approach for designing polymers has been extensively reported. Recently, several examples of NFSMAs containing conformational locks have been presented in the literature. This situation encourages us to perform a detailed theoretical investigation in designing planar small molecular acceptors. Various nonbonding interactions were studied using accurate computational methods, and molecules with multiple nonbonding interactions showed high planarity. Planar acceptors showed red-shifted absorption with high oscillator strengths. In addition, backbone planarity plays a very important role in tuning the charge transport properties and decreasing reorganization energy. Our results could provide important information to guide the further design of promising NFSMA materials.

Triphenylamine-Based Fluorescent Styryl Dyes: DFT, TD-DFT and Non-Linear Optical Property Study

The electronic structures and spectroscopic properties of triphenylamine-based monostyryl and bis(styryl) dyes were studied using quantum chemical methods. The ground-state geometries of these dyes were optimized using the density functional theory (DFT) method. The lowest singlet excited state was optimized using time-dependent density functional theory (TD-DFT). The absorption was also calculated using the ground-state geometries. All the calculations were carried out in the gas phase and in solvent. The results indicate that the absorption maxima calculated using the TD-DFT are in good agreement with those obtained experimentally. These dyes possess a large second-order non-linear property and this is mainly due to the strong donor-π-acceptor conjugation which is attributed to the excited state intramolecular charge transfer (ICT). There is a relationship between the hardness and first hyperpolarizability and second hyperpolarizability of mono- and bis(styryl) dyes. The efficiency of the intersystem crossing process can be improved by reducing the energy gap between the singlet and triplet excited states.

Second order hyperpolarizability of triphenylamine based organic sensitizers: a first principle theoretical study

Designed metal-free dyes have been investigated by Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) to evaluate the ground state and excited state geometries of triphenylamine-based organic sensitizers.