Time evolution of the solvated and conformationally relaxed emissive excited state of the anionic form of salophen, a Schiff base

• Published in: Journal of the Indian Chemical Society Vol. 98; no. 9; p. 100122
• Main Authors: Dasgupta, Souradip, Chowdhury, Arkaprava, Datta, Anindya
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-09-2021
• Subjects: Conformational relaxation; Femtosecond optical gating; Fluorescence; Fluorogenic molecules; Solvation dynamics; Conformational relaxation; Fluorescence; Fluorogenic molecules; Femtosecond optical gating; Solvation dynamics
• ISSN: 0019-4522
• DOI: 10.1016/j.jics.2021.100122

Salophen is a weakly fluorescent Schiff base which forms emissive co-ordination complexes with Zn2+ and Al3+. The complex with Al3+ is significantly more fluorescent than that with Zn2+, presumably because the dimeric complex with Zn2+ is associated with additional nonradiative channels. This contention has been put to test, through a careful investigation of excited state dynamics of the anionic form of salophen (Sal2−), which is the form in which the ligand exists in the complexes. The emissive excited state of the anion (Sal2−) has been found to be solvated and conformationally relaxed, over tens of picosecond. It is significantly more fluorescent than the neutral compound, with fluorescence lifetime that is longer by almost two orders of magnitude. Fluorescence lifetime of the anion is in fact longer than that of the complex with Zn2+ and slightly less than that of the complex with Al3+. So, the earlier hypothesis about additional nonradiative deactivation pathways in the Zn2+ complex gains credence from the present study.
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•Fluorescence lifetime of the anionic form of salophen is significantly longer than the reported lifetime of its neutral form.•The emissive excited state of the anionic form of salophen undergoes solvation and conformational relaxation in picosecond time scale.•While the fluorescence lifetime of the anion is shorter than that of the aluminium complex, it is longer than that of the zinc complex. This observation fortifies the contention of additional non radiative pathways that open up in the Zinc complex due to π- stacking.