Abstract
A new white-light-emitting molecule (1) was synthesized and characterized by NMR spectroscopy, high resolution mass spectrometry, and single-crystal X-ray diffraction. Compound 1 crystallizes in the orthorhombic space group Pnma, with a = 12.6814(6), b = 7.0824(4), c = 17.4628(9) Å, α = 90°, β = 90°, γ = 90°. In the crystal, molecules are linked by weak intermolecular C-H···O hydrogen bonds, forming an infinite chain along [100], generating a C(10) motif. Compound 1 possesses an intramolecular six-membered-ring hydrogen bond, from which excited-state intramolecular proton transfer (ESIPT) takes place from the phenolic proton to the carbonyl oxygen, resulting in a tautomer that is in equilibrium with the normal species, exhibiting a dual emission that covers almost all of the visible spectrum and consequently generates white light. It exhibits one irreversible one-electron oxidation and two irreversible one-electron reductions in dichloromethane at modest potentials. Furthermore, the geometric structures, frontier molecular orbitals (MOs), and the potential energy curves (PECs) for 1 in the ground and the first singlet excited state were fully rationalized by density functional theory (DFT) and time-dependent DFT calculations. The results demonstrate that the forward and backward ESIPT may happen on a similar timescale, enabling the excited-state equilibrium to be established.
Highlights
Excited-state intramolecular proton transfer (ESIPT) molecules have been drawing significant attention due to their unusual optical properties [1,2,3,4,5,6]
The results clearly show that upon electronic excitation of 1, the hydroxyl proton (O(2)-H(2A)) is expected to be more acidic, whereas the carbonyl oxygen O(1) is more basic with respect to their ground state, driving the proton transfer reaction
The forward and the backward ESIPT may happen on a similar timescale, and leads to the rapidly established excited-state equilibrium
Summary
Excited-state intramolecular proton transfer (ESIPT) molecules have been drawing significant attention due to their unusual optical properties [1,2,3,4,5,6]. The resulting proton-transfer tautomer is totally different in structure and electronic configuration from its corresponding ground state, that is, a large Stokes shifted K* Ñ K fluorescence This unique optical property has many potential applications, typical examples of which are probes for solvation dynamics and biological environments [11,12,13,14], fluorescence microscopy imaging [15], photochromic materials [16], chemosensors [17,18,19,20,21], nonlinear optical materials [22], near-infrared fluorescent dyes [23], and organic light-emitting diodes (OLEDs) [24,25,26].
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