Synthesis, Characterization, and Crystal Structures of Imides Condensed with p-Phenylamino(Phenyl) Amine and Fluorescence Property

Abstract

A series of aromatic diimide and monoimide compounds condensed with p-phenylamino(phenyl)amine were synthesized and confirmed by Proton Nuclear Magnetic Resonance (¹H NMR), Carbon-13 Nuclear Magnetic Resonance (¹³C NMR), Fourier Transform Infrared Spectroscopy (FT-IR), Elemental Analysis (EA), and High Resolution Mass Spectroscopy (HRMS). Meanwhile, single crystal X-ray diffraction showed the existence of intermolecular N···O hydrogen bonds, which affected the thermal stabilities of corresponding compounds by the support of Thermalgravimetric Analysis (TGA) curves. The steady-state UV-vis absorption peaks of synthetic compounds 1-6 appeared in the range of 220-380 nm. Fluorescence emission spectra showed peaks in the range of 290-420 nm. Meanwhile, deep-blue or violet-blue emissions for 2, 4, and 5 in THF under excitations of 254 nm and 365 nm, respectively, were observed at room temperature in air. Furthermore, Differential pulse voltammetry (DPV) and cyclic voltammogram CV were conducted within -1.5-+1.5 V to show quasi-reversible behavior for conjugated compounds and irreversible behavior for less conjugated ones.

Keywords: X-ray crystal structure; electrochemistry; fluorescence; hydrogen bond; imide; p-phenylamino(phenyl)amine.

Scheme 1

Synthesis of diimide and monoimide compounds.

Figure 1

Schematic diagrams of intermolecular N···O hydrogen bonding interactions that appeared in diimide compounds for 1 (top left), 3 (middle left), and 5 (bottom left). ORTEP structures of 1 (top right), 3 (middle right), and 5 (bottom right) were presented with intermolecular N···O hydrogen bonding interactions. Solvent DMF molecules in 1 were deleted for clarity. Ph-t represented the terminal phenyl unit and Ph-a represented the adjacent phenyl unit relative to core.

Figure 2

Space filling diagrams (left) with listed torsion angles and dihedral angles (right) were presented. Top left and right diagrams are for 1, middle left and right diagrams are for 3; bottom left and right are for 5.

Figure 3

Perspective views for 1 formed by intermolecular N···O hydrogen bonds (a–d) are presented. A large pore was formed by four molecules with equivalent one type of N···O hydrogen bonds (a). Views of embedded solvent DMF molecules (b), solvent free 2D network (c), and channels (d) are presented. The greenish blue dashed line represents the intermolecular N···O hydrogen bonds. The red dashed line represents hanging contacts.

Figure 4

Perspective views for 3 formed by intermolecular N···O hydrogen bonds (a–d) are presented. A small pore was formed by two molecules with non-equivalent two types of N···O hydrogen bonds (a). Views of a single 1D chain (c), and double chains (b,d) for 3 are presented. The greenish blue dashed line represents intermolecular N···O hydrogen bonds.

Figure 5

UV-vis absorption spectra (top), excitation spectra (bottom left, dashed line) and emission spectra of 1–6 (bottom right, solid line) in THF (2 × 10⁻⁵ M) were recorded at room temperature in air. Excitation wavelengths of 265 nm for 1, 277 nm for 2, 274 nm for 3, 300 nm for 4, 278 nm for 5, and 273 nm for 6 were applied to obtain emission spectra.

Figure 6

Emission photographs of solvent THF (most left) and 1–6 in THF, excited at 254 nm (top) and 365 nm (bottom), were recorded at room temperature in air.

Figure 7

Normalized emission spectra of 1 were excited at 286 nm in CH₃CN (black), EtOH (red), THF (blue), and DCM (greenish blue) at room temperature in air.

Figure 8

Differential pulse voltammetry (DPV) in the black dashed line and a cyclic voltammogram (CV) of 1 were measured in DMF with 0.1 M TBAPF₆. The CV of 1-Oxi in the red solid line indicates that oxidation was run first and the 1-Red in the blue solid line indicates that reduction was run first. Pt wire, Pt disk, and Ag/AgCl were used for measurements with a scan rate of 0.1 Vs⁻¹.