Synthesis and spectroscopic characterization of novel GFP chromophore analogues based on aminoimidazolone derivatives

Abstract

In order to improve the fluorescence properties of the green fluorescent protein chromophore, p-HOBDI ((5-(4-hydroxybenzylidene)-2,3-dimethyl-3,5-dihydro-4H-imidazol-4-one), sixteen dihydroimidazolone derivates were synthesized from thiohydantoin and arylaldehydes. The synthesis developed is an efficient, novel, one-pot procedure. The study provides a detailed description of the spectroscopic characteristics of the newly synthesized compounds, using p-HOBDI as a reference. The new compounds all exhibited significantly stronger fluorescence than p-HOBDI, up to 28 times higher quantum yields. An experimental and theoretical investigation of the relationship of the fluorescence properties with the molecular structure was also carried out. A good correlation was found between the emission wavenumber and the Hammett constant of the functional group, which suggests the intermolecular charge transfer (ICT) mechanism between the aromatic groups.Graphical abstract *Manuscript Click here to download Manuscript: AJancso_Spectrochimica_A_20181201_V1.pdf Click here to view linked References

Synthesis and Fluorescence Mechanism of the Aminoimidazolone Analogues of the Green Fluorescent Protein: Towards Advanced Dyes with Enhanced Stokes Shift, Quantum Yield and Two‐Photon Absorption

“…In this study, 10 novel compounds ( 1 b – k , listed in Table 1) were designed and synthesised from 2‐thiohydantoin ( 2 ) in two‐step procedures (Figure 2) to enhance the fluorescent activity of the GFP analogue scaffold 1 a . The preceding study revealed the beneficial spectroscopic change of the OH group at position 4 on the benzylidene phenyl ring [31] . Another work showed significant improvement in the Stokes shift when OH was placed to position 2 [3] .…”

“…Our recent study revealed that the introduction of a conjugative group (e. g. phenylamino group) to the imidazolone ring enables the fluorescence of the para ‐amino derivatives and it enhances their QY even above that of p ‐HOBDI [31] . The introduction of electron donor substituents into the p ‐HOBDI structure has also been studied to improve the QY, upshift the emission wavelength and increase the Stokes shift.…”

“…The introduction of electron donor substituents into the p ‐HOBDI structure has also been studied to improve the QY, upshift the emission wavelength and increase the Stokes shift. For instance, the change of the 4‐hydroxy group to a 4‐diethylamino group on the phenyl ring improved the QY by up to 28 times [31–33] . An even more remarkable boost in fluorescence is displayed by the amino derivatives in aprotic solvents, out of which the meta‐amino isomer was shown to have an unusually high, 0.46 QY [2,13,34] .…”

“…Solvent‐ and pH‐related effects are also often enhanced by the substituents. For example, solvatofluorochromicity is observed in aprotic solvents and hydrogen‐bond‐mediated fluorescence quenching is happening in protic solvents [2,31] . It was also found that ESPT [35] or in certain cases, excited‐state intramolecular proton transfer (ESIPT) [36] and internal charge transfer (ICT) [31] may also play an essential role in determining the fluorescence properties of the planar GFP‐like chromophores.…”

“…For example, solvatofluorochromicity is observed in aprotic solvents and hydrogen‐bond‐mediated fluorescence quenching is happening in protic solvents [2,31] . It was also found that ESPT [35] or in certain cases, excited‐state intramolecular proton transfer (ESIPT) [36] and internal charge transfer (ICT) [31] may also play an essential role in determining the fluorescence properties of the planar GFP‐like chromophores. Many orthogonal structural modifications of p ‐HOBDI can be found in the literature, also aiming to improve the fluorescence property [37–44] .…”