Understanding the role of symmetric/asymmetric curcuminoids in designing efficient optical, nonlinear optical and photovoltaic materials.

The curcuminoid class of organic compounds is very versatile which possesses applications over vast fields of science and technology. In the present investigation, we systematically designed six curcuminoid (Crmd) derivatives with symmetric and asymmetric structures, which are named as Crmd-1 to Crmd-6. We used 2,2-difluoro-4,6-divinyl-dioxaborinine moiety as a linker to design symmetric and asymmetric donor π-conjugation and acceptor configurations. Triphenylamine and triphenylborane are used as donor and acceptors which are intrinsically donor and acceptors owing to the presence of vacant p-orbital in boron and lone pair of electrons in nitrogen atoms, respectively. Density functional theory (DFT) is applied using M06/6-311G* method to calculate linear polarizability (α), and second hyperpolarizability (γ). The value of isotropic linear polarizability (αiso) and anisotropic linear polarizability (αiso) are 125.3 × 10–24 esu and 148.1 × 10–24 esu for Crmd-6, respectively. By comparative analysis, it is observed that the highest value of γ amplitude is calculated to be 6472.3 × 10–36 esu for Crmd-6. The robust increase in non-linear optical (NLO) polarizability is observed due to the asymmetric intramolecular charge transfer (ICT) and better D-π-A configuration in Crmd-6. Time dependent DFT calculations are performed to observe the origin of third-order NLO polarizabilities. Furthermore, frontier molecular orbitals, electron density difference, molecular electrostatic potential diagrams, and transition density matrix analysis demonstrate enhanced charge redistribution from the donor to the acceptor fragments. The use of modern computational tools highlights an effective ICT, which leads stronger third-order NLO response properties in designed curcuminoid derivatives. [ABSTRACT FROM AUTHOR]