Immobilization of dipyrenylphosphinic acid to boehmite: Fluorescent hybrid with weakened pyrene-aggregation

Abstract

Ethyldipyrenylphosphate (DPyPOOEt) was designed and synthesized by utilizing ethyldichlorophosphate as the core and 1-bromopyrene as substituting groups, and afterwards dipyrenylphosphinic acid (DPyPOOH) was synthesized by the hydrolysis reaction of DPyPOOEt by using bromotrimethylsilane (TMSBr). Fluorescent hybrid was finally prepared by the dehydration condensation between DPyPOOH and hydroxyl groups on the surface of boehmite. The chemical structure of DPyPOOEt and DPyPOOH were characterized by 1H NMR and 13C NMR. Crystal structure, chemical structure and microtopography of hybrid were characterized by X-ray diffraction spectra (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM), respectively. The results demonstrate that the incorporation of two pyrene substituent groups into phosphine oxide can be successfully immobilized on the surface without any change of crystal structure of boehmite. Fluorescence spectra in solution and powder further demonstrated the occurrence of shape-changed and red-shifted emission peaks of DPyPOOEt and DPyPOOH than that of pyrene. In particular, compared to DPyPOOEt and DPyPOOH in solid, the hybrid shows blue-shifted fluorescence. Optimized molecular conformation, ground electronic structure of DPyPOOEt has been investigated in detail by quantum chemistry method. The introduction of phosphine oxide tunes the conjugated structure of pyrene-ring and spatial conformation between the pyrene-ring. In addition, intramolecular V-shanped conformation when DPyPOOH confined to boehmite surface reduce π-π aggregation between pyrene rings. Therefore, these results indicate that the hybrid is expected to highly efficient blue light-emitting material.