Aggregation Induced Emission-Active Ferrocene Appended Naphthalimide and Phthalimide Chromophores for Mechanochromic...

A new ferrocene (Donor) phenyl (π) conjugated phthalimide and naphthalimide (Acceptors) chromophores, Fc-Ph-PI (1) and Fc-Ph-NI (2), were synthesized and characterized. Single-crystal X-ray diffraction studies revealed that chromophore 2 crystallizes centrosymmetric monoclinic P2₁/n space group with non-covalent interactions (intermolecular hydrogen bonding and CH…π interactions), which favors SHG efficiencies. The solvatochromic studies were conducted to elucidate the intramolecular charge-transfer (ICT) process, which results in a 46 nm blueshift in the emission spectra of chromophore 2 relative to its absorption spectra, due to a higher ground-state dipole moment. The aggregation-induced emission (AIE) studies in THF/H₂O mixture at 90% showed enhanced emission for chromophore 2 due to restricted intramolecular rotation (RIR). Additionally, chromophore 2 exhibited mechanofluorochromic and acidochromic behavior, which resulted in an increased emission maximum and intensity. The second-order non-linear optical (NLO) property of the chromophores was studied using Kurtz Perry powder technique, utilizing KDP as a standard reference. Chromophore 2 exhibits 1.35 times higher Second Harmonic Generation (SHG) efficiency than chromophore 1, attributed to efficient charge transfer facilitated by enhanced π-extension of the naphthalimide acceptor. Furthermore, density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations were performed to validate the experimental results using B3LYP/6-31+G** level of theory.