Exploring the impact of central core modifications among several push-pull configurations to enhance nonlinear optical response.

The present study explores a series of novel donor-π-acceptor (D-π-A) molecules containing 4,4′-dimethyldiphenylamine moiety as donor, 4,4′-dinitrodiphenylborane as acceptor while different π-bridges as efficient linkers between them, which comprises of (− HC CH −) n , (− Ph −) n and (− Ph ̶ HC CH −) n combinations for compounds in series 1, 2 and 3, respectively. Quantum chemical computations are applied to calculate the linear polarizability (α), first (β) and second (γ) hyperpolarizabilities. A comparative analysis is performed considering an increase of NLO polarizabilities as a function of different π-linkers. Among the investigated compounds, 3c shows the largest first and second hyperpolarizabilities of 1378 × 10−30 and 34971 × 10−36 esu, respectively. Interestingly, an increase in NLO polarizability is observed by modifying the π-conjugated bridges and the largest NLO polarizability is observed for series 3 possessing (Ph ̶ HC CH −) n π-linker which is found due to its lower transition energy and higher oscillator strengths. Furthermore, TD-DFT investigations, frontier molecular orbitals (FMOs) and electron density difference (EDD) maps analysis have shown a more efficient intramolecular charge transfer character from donor to acceptor moieties through (Ph ̶ HC CH −) n π-linkers. The density of states (DOS) maps are showing explicit contributions of electronic states from different fragments of a molecular system where the partial contributions of (Ph ̶ HC CH −) n π-linkers is seen significant in HOMO-LUMO orbitals of all the systems in series number 3. Thus, we believe that our study will highlight the importance of different D-π-A chromophores having variant types of π-conjugation cores as discussed in the present investigation. Schematic and graphical description of the designed D-π-A molecules. Image 1 • Three series of novel D-π-A molecules consisting of (HC=CH) n , (Ph) n and (Ph ̶ HC=CH) n combinations • The NLO polarizabilities are calculated using DFT methods. • All the designed series of compounds show reasonably larger NLO responses. • A structure-NLO property relationship is examined using TD-DFT, FMOs and EDD maps. [ABSTRACT FROM AUTHOR]