Key Electronic, Optical Nonlinearity and Structural Insights Into Brominated Spiropyrrolidines: A Combined SC‐XRD and DFT Study

ABSTRACT Currently, structural and optoelectronic properties of two brominated spiropyrrolidines, SPD1 (3’‐(4‐bromobenzoyl)‐1’‐methyl‐4’‐(naphthalen‐2‐yl)spiro[indoline‐3,2’‐pyrrolidin]‐2‐one) and SPD2 (3’‐(4‐bromobenzoyl)‐1’‐methyl‐4’‐ferrocenylspiro[indoline‐3,2’‐pyrrolidin]‐2‐one) were investigated. Structural validation was accomplished via single‐crystal X‐ray diffraction (SC‐XRD), whereas key electronic and NLO properties were investigated through DFT/TD‐DFT approaches at the M06/6‐311G( d,p ) level. The N‐H bond in entitled crystals indicated the strong hydrogen bonding interactions which stabilized the crystal lattice. Further, the intermolecular interactions calculated through Hirshfeld surface analysis played a significant role in stability and crystal packing. Among synthesized crystals, SPD1 , having a naphthalene moiety, displayed the smallest energy gap (4.244 eV) with greater softness value, illustrated good charge transfer aptitude, resulting in high polarizability and improved NLO response compared to SPD2 , having ferrocene unit. Comparative study with urea, a standard reference for NLO investigation, confirmed the greater hyperpolarizability of entitled spiropyrrolidines. These results suggest the potential utilization of SPD1 and SPD2 in optoelectronic and NLO applications.