Fluorescence Properties Reinforced by Proton Transfer in the Salt 2,6-Diaminopyridinium Dihydrogen Phosphate

Abstract

Luminescent materials have many interesting applications, but it remains difficult to control the luminescence of organic materials and in particular to retain the same luminescence in solution and in the solid state, a property of interest for various imaging applications. In the present work, the fluorescent properties of the salt of 2,6-diaminopyridinium with dihydrogen phosphate have been explored. As a result of proton transfer from phosphoric acid to the pyridine nitrogen and the stabilizing effect of the two primary amines at the positions ortho to the pyridine nitrogen, the band gap between the HOMO and the LUMO is considerably diminished in comparison with that in 2,6-diaminopyridine. This is confirmed by a red shift in its absorption spectrum. Because protonation is retained in aqueous solution, the dissolved 2,6-diaminopyridinium dihydrogen phosphate salt retains a similar fluorescent spectrum as in the solid state. The crystals have been studied by single-crystal X-ray diffraction; FTIR, Raman, UV-vis-NIR, and luminescence spectroscopy; HOMO-LUMO calculations using DFT; and thermal analysis. The compound provides an example of a supramolecular motif that controls the crystal structure and the luminescence properties. In addition, the crystal exhibits negligible thermal expansion over a temperature interval of 150 °C. In short, 2,6-diaminopyridinium dihydrogen phosphate is an interesting compound for the design of luminescent devices.

Crystal packing, vibrational studies, DFT calculations of a new hybrid nickel (II)‐complex and its application in Heck and Sonogashira cross‐ coupling reactions

“…According to our previous results, the stretching modes of the bands C=C and C=N of the pyridine ring are observed in the region between 1650‐1400 cm ‐1 . In our case, we noted a strong band in the FT‐IR spectrum at 1608 cm ‐1 and a very high intensity peak at 1477 cm ‐1 , assigned to C=C stretching vibrations.…”

“…For visual comparison, the observed and simulated IR and Raman spectra of the [Ni(dmpy)(H 2 O) 4 ]SO 4 are given in Figure and Figure . All the bands observed were assigned by comparison with the spectrum of other compounds . All the IR and Raman bands of this crystal observed in the region below 300 cm ‐1 must be due to external vibrations.…”

Exploration of the Luminescence Properties of Organic Phosphate Salts of 3‐Quinoline‐ and 5‐Isoquinolineboronic Acid

“…The transference of one of the protons of the starting 1‐naphthyl phosphate to the nitrogen atoms of 3QBA and 5IQBA , respectively, results in the formation of additional heterodimeric synthons, which are characterized by the simultaneous presence of a strong N + –H ··· – O/O and a weak C‐H ··· O hydrogen bond (motif B , Scheme ). The N ··· O distances in 3QBA‐1NP and 5IQBA‐1NP are 2.651(1) and 2.629(2) Å, respectively, being significantly shorter than the analogous distances reported by Mani et al for the 2,6‐diaminopyridinium salt of dihydrogen phosphate (2.748(2) Å) . There is a simple method to determine if pyridine rings are neutral or ionized.…”

“…The shift of ν(B–O) and ν(B–C) to higher wavenumbers in relation to the starting boronic acids (Table ) is in accordance with a weaker O‐H bond due to the interaction with the hydrogen phosphate anions in synthon A (Scheme ). Similarly, organic phosphoric acid esters exhibit characteristic bands for the ν(P=O) and ν(P–O) stretching vibrations,, which for 1NP and DPP are located at 1243/767 and 1187/775 cm –1 , respectively. In the boronic acid salts with 1NP and DPP one of the P–OH groups is deprotonated, giving intense ν(P–O) bands in the range of 748–774 cm –1 .…”

Stabilization of Tetrachloride with Mn (II) and Co (II)Complexes and 4-Tert-Butylpyridinium Organic Cation: Elaboration of the Structure and Hirshfeld Surface, Optical, Spectroscopic and Thermal Analyses

“…It can be seen that most of the organic cations do not give rise to bands in the visible domain [59][60][61][62]. The LMCT phenomenon (ligand-to-metal charge transfer) between the chloride atom Cl and metal atom Co can be observed in two bands located at 423 and 469 nm [63][64][65][66][67][68][69]. The bands located at 542, 558 and 576 nm are intended for d-d electronic transitions, showing that the geometry of the cobalt atom contain stetrahedral [CoCl 4 ] 2− ( 4 A 2 (F)→ 4 T 2 (F), 4 A 2 (F)→ 4 T 1 (F) and 4 A 2 (F)→ 4 T 1 (P), which are generally attributed to compounds based on cobalt Co (II) [70][71][72].…”