Refined Structure Determination of Blue-Emitting Tris(8-hydroxyquinoline) Aluminum(III) (Alq₃) by the Combined Use of Cross-Polarization/Magic-Angle Spinning ¹³C Solid-State NMR and First-Principles Calculation

Abstract

The combined use of cross-polarization/magic-angle spinning (CP/MAS) 13C NMR experiments and gauge-including projector-augmented wave (GIPAW) isotropic chemical shift calculations is an easy and useful method for the structural refinement of organic aggregates. In this study, the method is applied to an important material for organic light-emitting diodes, tris(8-hydroxyquinoline) aluminum(III) (Alq3). CP/MAS 13C NMR spectra include precise structural information of not only the conformation of the molecules but also the intermolecular packing. First, the structural refinements were performed for the Alq3 in the γ- and δ-crystalline forms employing the combined method. Second, information on intramolecular structures and intermolecular structures was distinguished by comparing GIPAW calculations for crystals under periodic boundary conditions and those for isolated molecules extracted from the crystals. It was found from the analysis that the γ-Alq3 and δ-Alq3 crystals have similar intramolecular structures both in the facial isomeric state, whereas their intermolecular packing is significantly different. Both the γ-Alq3 and δ-Alq3 crystals exhibit unusual blue emission, which is different from conventional green emission, and the origin of the difference has been debated. This investigation shows that the origin of the blue-shifted emission is the isomeric states of Alq3, not the intermolecular packing.

Bio-recognitive photonics of a DNA-guided organic semiconductor

“…The XRD pattern of the ssDNA-Alq 3 rod showed typical α-phase peaks for Alq 3 at 11.40° and 12.81°, along with a δ-phase peak at 11.79°. Hence, the ssDNA-Alq 3 rods fabricated in this study contain both α- and δ-phases 8 9 25 26 27 , which is consistent with the yellowish-green luminescence observed in the PL analyses. Upon interaction with specific tDNA molecules, the rods showed an XRD pattern almost identical to that of the initial Alq 3 rods, except that two additional peaks appeared at 10.59° and 13.31°.…”

Mesoporous silica (KIT-6) derivatized with hydroxyquinoline functionalities as a selective adsorbent of uranium(VI)

“…Figure 3 shows CP/MAS 13 C NMR spectra of KIT-6-quinoline-8-ol and KIT-6-quinaldine-8-ol. All carbon species of the two modified KIT-6 are assigned appropriately, and the results confirm that KIT-6 was modified successfully [42][43][44]. The 13 C CP-MAS NMR spectrum of grafted KIT-6 shows three peaks at 13.3, 26.7, and 47.7, 50 ppm, respectively, representative of four methylene carbons.…”

Ex Cathedra Immobilization of 8-Hydroxyquinoline to Inorganic Carriers via a New Silane Coupling Reagent for Extractive Sample Cleanup of Iron(III)

“…The spectrum also contains one peak for aliphatic carbon (1.272 ppm for two CH 3 groups attached to silicon). C-8 of the oxine part appears near 150 ppm. , The introduction of −OH at C-8 in the unsubstituted quinoline changes the chemical shifts (δ) by −10.74, −18.36, and −10.23 ppm for C-9, C-7, and C-5, respectively, placing them at 138.54, 111.50, and 118.23 ppm, respectively, as in the earlier-reported 13 C spectrum . Upon the introduction of the −NN– group at C-5 in the oxine (see the Figure b inset), the electronic environments of C-9, C-7, and C-5 are further affected, and the peaks appear at 92.456, 122.338, 123.437 ppm in the present 13 C NMR spectrum.…”