The role of substituted pyridine Schiff bases as ancillary ligands in the optical properties of a new series of fac-rhenium(i) tricarbonyl complexes: a theoretical view

Abstract

Over the last few years, luminescent Re(i) tricarbonyl complexes have been increasingly proposed as fluorophores suitable for fluorescence microscopy to visualize biological structures and cells.

Intramolecular Hydrogen Bond in Pyridine Schiff Bases as Ancillary Ligands of Re(I) Complexes Is a Switcher between Visible and NIR Emissions: A Relativistic Quantum Chemistry Study

“…By contrast, PSB2 to PSB4 present the −OH in the ortho position with respect to the azomethine link, which would favor the formation of the IHB. Since the presence of highly electronegative halogens (F or Cl) vicinal to −OH impairs the formation of IHB, apparently acting as a switch between the visible and NIR emissions, 11 we wanted to determine whether the presence of other halogens can disrupt the IHB, potentially affecting the emission. Thus, we are interested in comparing Re(I) complexes (Figure 1) concerning their predicted absorption and emission, Stoke's shift, and luminescent lifetimes (τ), among other characterizations aimed to better understand the role of the IHB in the emission modulation.…”

“…11 Recently, it has been shown that the presence of a strongly electronegative halogen (F or Cl) in position 6 visible range to the NIR range. 11 These results suggest a role of the IHB as an important switcher between visible and NIR emissions in this kind of complexes. Since PSBs can be substituted to modulate the properties of the whole Re(I) complex, it is necessary to explore whether other substitutions can also affect the photophysical properties, mainly the emission range.…”

“…8−10 In particular, PSBs harboring an intramolecular hydrogen bond (IHB) are very attractive, especially with walled cells. [2][3][4][5]11,12 Although the role of the IHB in cell uptake and staining properties is hard to determine in biological models, its contribution to photophysical properties of the whole complex has already been described by a theoretical study of Re(I) tricarbonyl complexes harboring PSBs. 11 Recently, it has been shown that the presence of a strongly electronegative halogen (F or Cl) in position 6 visible range to the NIR range.…”

“…[2][3][4][5]11,12 Although the role of the IHB in cell uptake and staining properties is hard to determine in biological models, its contribution to photophysical properties of the whole complex has already been described by a theoretical study of Re(I) tricarbonyl complexes harboring PSBs. 11 Recently, it has been shown that the presence of a strongly electronegative halogen (F or Cl) in position 6 visible range to the NIR range. 11 These results suggest a role of the IHB as an important switcher between visible and NIR emissions in this kind of complexes.…”

“…2−5 Although biocompatibility must be empirically determined directly by working with cell models, due to their complexity, photophysical properties can be predicted using quantum chemical calculations with a good approximation to experimental data. 11,15,16 In this work, we present a relativistic theoretical analysis of two series of fac-[Re(CO) 3 (N,N)PSB] 1+ complexes to predict the role of the IHB in the ancillary ligand concerning their photophysical behavior. N,N corresponds to 2,2′-bipyridine (bpy) (series A) or 4,4′-bis(ethoxycarbonyl)-2,2′-bipyridine (deeb) (series B) (Figure 1).…”