Ferrocene conjugated Y-shaped imidazole push-pull chromophores: Structural, luminescence, theoretical, linear and nonlinear optical studies

Abstract

The development of molecular based second order non-linear optical (NLO) chromophores is an exciting discipline with important applications such as optical data storage, telecommunications, optical switch, electro-optic modulator, and NLO bioimaging [1]. Ferrocene conjugated Y-shaped push-pull chromophores 1-6 were synthesized and spectroscopically characterized. The structure of the chromophores 5 and 6 were confirmed by the single crystal X-ray diffraction studies, and it crystallized in a triclinic crystal system with a P-1 centrosymmetric space group. It exhibits several non-covalent interactions in the crystal packing [2]. The solvatochromic studies of chromophores 1-6 showed positive solvatochromism with red-shift from non-polar to polar solvents, due to the high dipolar excited state from the presence of strong electron-donor and acceptor moieties. The electrochemical performance of the chromophores revealed that the one-electron transfer from the ferrocene to ferrocenium ion (Fe²⁺/Fe³⁺). The chromophores 1-6 exhibited low fluorescence intensity due to the quenching nature of ferrocene and then enhanced emission was observed in the aggregation-induced emission (AIE) process, because of the restricted intramolecular rotation. The nonlinear optical response was attained by the Kurtz-Perry powder technique and KDP was used as standard. The second harmonic generation (SHG) efficiency of chromophore 4 shows higher than the others due to the presence of strong donors. In addition, the experimental results were validated with theoretically by DFT/TD-DFT using the B3LYP/6-31+G** level of theory and will be presented.

Fig.1. (a)Single crystal structure of the chromophore 6 and (b) SHG efficiencies of the chromophores.