Effect of multi-donor and extended π-conjugation in ferrocene appended indanedione chromophores for aggregation induced emission enhancement (AIEE) and nonlinear optics

• Published in: Dyes and pigments 2024-12, Vol.231, p.112422, Article 112422
• Main Authors: Subiksha, Vengidusamy Srinivasan, Viswanathan, Thamodharan, Prabu, Selvam, Palanisami, Nallasamy
• Format: Article
• Language: English
• Subjects: Aggregation induced emission enhancement (AIEE); DFT calculations; Donor-π-Acceptor; Ferrocenyl indanedione; Non-linear optics; Thin film
• ISSN: 0143-7208
• DOI: 10.1016/j.dyepig.2024.112422

A new (D-D’π-A) type ferrocene and methoxyphenyl (D-D′) conjugated indanedione (A) based linear and π-extended multi-donor-π-acceptor chromophores 1–4 were synthesized and characterized. The chromophores 2–4 were further investigated by single-crystal analysis through X-ray diffraction, revealing centrosymmetric space groups with non-covalent interactions (inter, intramolecular hydrogen bonding, and C–H…π interactions) and these molecular packing interactions favor SHG efficiencies. Electrochemical studies show the one-electron charge transfer (Fe2+⇌Fe3+) and observed greater redox potential of chromophore 4 than the parent ferrocene due to the substitution effect. The solvatochromic studies in emission spectra resulted in redshift (56–109 nm) for the chromophores 1–4 by increasing the solvent polarities, which indicates higher excited state stabilization relative to the ground state, results effective intramolecular charge transfer process within the chromophores. The occurrence of ferrocene moieties lowers the fluorescence intensities of the chromophores 1–4, which was overcome through aggregation induced emission enhancement (AIEE) studies at 60 % (THF/H2O). The AIEE state also shows 23 times higher quantum yield than the THF solution for chromophore 4. In addition, a thin film using polymethyl methacrylate as a binder shows a significant blue shift with higher emission intensity than those obtained in the solution due to the intermolecular interactions and enhancement of viscosity. The SHG efficiency studied using the Kurtz and Perry powder technique results in a higher value for chromophore 4 (2 times higher than the reference KDP) attribute to the multi donors, acceptor, and extended π conjugation reducing the anti-parallel alignment in the solid state. The computational calculations were done to validate the experimental results using B3LYP/6-31+G** level of theory. The enhanced SHG efficiencies with increased fluorescence intensity in the AIE state were observed in the multi-donor-π-acceptor (D-D′-π-A) based push-pull chromophores. [Display omitted] •AIEE active ferrocenyl chromophores 1–4 were structurally analyzed.•The significant solvatochromic shift in emission spectra indicates a higher excited state dipole moment.•Enhanced emission was achieved by the AIEE process using THF/water mixture at 60 % and also in a thin film state.•Chromophore 4 shows higher SHG efficiencies due to the multi-donor π acceptor system, which also shows similar trends