Zinc(II) bis(dipyrromethenate)s crystal solvates with dimethyl sulfoxide Composition, stability and spectral-luminescent properties

It was found that 3,3′-, 2,3′ and 2,2′-zinc(II) bis(dipyrromethenate)s ([Zn2L2]) form stable supramolecular complexes of the composition [Zn2L2(DMSO)n] (n = 1 or 2) with dimethyl sulfoxide (DMSO). The [Zn2L2(DMSO)n] are stable in the solid phase and solutions. Composition, stability, and spectral-luminescent properties of the [Zn2L2(DMSO)n] crystal solvates were studied by means of FTIR, PXRD, 1H NMR, DOSY, absorption and fluorescence analyses. Spectroscopic studies showed that the quantum yields (φ) of [Zn2L2(DMSO)n] are lower (to ∼1.6–3.6 times) than quantum yields (φо) of [Zn2L2] in cyclohexane. Quantum-chemical study allowed to suggest the most likely mechanism of the DMSO molecules coordination on the coordinating centers of [Zn2L2]. It is demonstrated, that the high-energy coordination interactions (Zn − O) in [Zn2L2(DMSO)n] are the main cause of the fluorescence quenching of [Zn2L2] in the presence of DMSO. Fluorescence quenching of [Zn2L2] in the DMSO presence is based on the photoinduced electron transfer (PeT) mechanism. The obtained results are interesting for the development of new [Zn2L2] fluorescent sensors of the DMSO molecules.