Rational Design and Investigation of Nonlinear Optical Response Properties of Pyrrolopyrrole Aza-BODIPY-Based Novel Push-Pull Chromophores

Intramolecular charge transfer (ICT)-based chromophores are highly sought for designing near-Infrared (NIR) absorbing and emitting dyes, as well as designing chromophores for nonlinear optical (NLO) applications. The properties of these so-called ‘push-pull’ molecules could be tuned easily through modification of the electronic donor (D) and acceptor (A) groups as well as by the π-conjugating linker. This study presents rational design and quantum chemical investigation of the correlation between the structural attributes, electro-optical properties, and NLO characteristics of molecules with a D–π–A framework for applications in photonics. The one- and two-photon absorption (2PA), average linear polarizability (αav) as well as the first hyperpolarizability (β) of novel chromophores consisting of a Dimeric aza-Boron Dipyrromethene (aza-BODIPY) analogue known as pyrrolopyrrole aza-BODIPY (PPAB) as acceptor and Triphenylamine (TPA) or Diphenylamine (DPA) as electronic donor with thienyl or phenylene groups as linkers are studied. Additionally, the Hyper-Rayleigh Scattering (βHRS) which enables to directly estimate the second-order NLO properties is also calculated for these compounds with 1064 nm excitation in Acetonitrile solvent. Significant increase in the β with increasing solvent polarity indicates the role of ICT in shaping NLO response of these molecules. The two-photon absorption cross-section of studied molecules could also be enhanced through modulation of donor and linker combinations. Our findings show that the D–π–A molecules designed in the present work exhibit significantly larger hyperpolarizabilities values, compared to the standard p-Nitroaniline, making them suitable candidates for future NLO applications.