Exploration of the effect of multiple acceptor and π-spacer moieties coupled to indolonaphthyridine core for promising organic photovoltaic properties: a first principles framework.

Herein, the indolonaphthyridine-based molecules (INDTD1-INDTD8) with A-π-A-π-A configuration were designed by the end-capped modification of INDTR reference with various acceptors. The density functional theory (DFT) and time-dependent DFT (TD-DFT) analyses at M06/6-31G(d,p) level were reported in this research to explore their optoelectronic and photovoltaic features. Their geometrical structures were initially optimized at the afore-said level and followed by various calculations such as the frontier molecular orbitals (FMOs), UV-Visible, density of states (DOS), transition density matrix (TDM), binding energy (E), open circuit voltage (V) and fill factor (FF). Moreover, their global reactivity parameters (GRPs) were depicted by using the HOMO-LUMO band gaps obtained from the FMOs study. The tailored molecules demonstrated lower band gaps (2.183-2.269 eV) than INDTR (2.288 eV). They also showed bathochromic shifts in the visible region in chloroform (735.937-762.318 nm) and gas phase (710.384-729.571 nm) as compared to INDTR (724.710 and 698.498 nm, respectively). Further, intramolecular charge transfer (ICT) was demonstrated via the DOS and TDM graphical maps. Among all the entitled chromophores, INDTD7 showed significantly reduced band gap (2.183 eV), red-shifted absorption value (760.914 nm) in chloroform solvent and minimal E value (0.554 eV). The presence of -SOH groups on the terminal acceptors of INDTD7  may enhance the mobility of charges. The results suggested that the newly designed chromophores can be effective candidates for the future organic solar cell applications. Moreover, this study may encourage the experimentalists to develop photovoltaic materials.