BOIMPY: Fluorescent Boron Complexes with Tunable and Environment‐Responsive Light‐Emitting Properties

Abstract

A series of air-stable boron complexes 1-5 were prepared by using N-aryl iminopyrrolide ligands. Designed as minimalist structural mimics of the privileged BODIPY motif, these new BOIMPY (BOron complexes of IMinoPYrrolide ligands) fluorophores feature low molecular symmetry that promotes emission from CT-type excited states with large Stokes shifts and little self-quenching. Through comparative studies on the homologous set of compounds 1-4, we have confirmed that a delicate interplay between conformational twisting and donor-acceptor interaction dictates the mechanism of de-excitation, which responds sensitively to solvent polarity as well as protonation states. Over a wide visible spectral range, the structure-dependent light-emitting properties of BOIMPY molecules are well manifested, even in the solid-state. In order to exploit the environment-sensitive nature of CT-type emission, the BOIMPY motif was elaborated further into a bioprobe molecule 5. Live-cell fluorescence imaging studies have established that 5 is localized exclusively at lipid droplets to produce well-resolved staining patterns without affecting cell viability. These findings promise future elaboration of BOIMPY-based functional molecules for applications in biological imaging, chemical sensing, and molecular switching.

Fluorescence Quenching in BODIPY Dyes: The Role of Intramolecular Interactions and Charge Transfer

“…, was only reported in 2009), followed by an extensive synthetic efforts to functionalize the dye core and tune the chemical and photophysical properties . Alternatively, the success of BODIPY derivatives inspired the design of various similar compounds such as aza‐BODIPY, PODIPY, BODIHY, BOPHY, BOIMPY and others …”

Crystal structure and fluorescence study of (μ-N-[(3,5-dimethyl-1H-pyrrol-2-yl)methylidene]-N-{4-[(3,5-dimethyl-1H-pyrrol-2-yl)methylideneazaniumyl]phenyl}azanium)bis[difluoridoboron(IV)]

“…In addition, their structures can easily be modified and they are not easily affected by the environment (Loudet & Burgess, 2007). The success of BODIPY dyes has led to research on similar structures such as aza-BODIPY structures (Bodio & Goze, 2019), boron complexes of iminopyrrolide ligands (BOIMPY; Suresh et al, 2012Suresh et al, , 2015Lee et al, 2016), bis(difluoroboron)-1,2-bis{(pyrrol-2-yl)methylene}hydrazine (BOPHY; Boodts et al, 2018) structures and other novel organoboron fluorescence materials (Frath et al, 2014).…”

“…BOIMPY has a similar structure to BODIPY, in which the pyrrole ring is located in the same plane as the aromatic ring, the boron atom and the methylene bridge. More importantly, BOIMPY has the advantage of lower molecular symmetry, which can overcome the shortcoming of the short Stokes shifts of BODIPY (Lee et al, 2016). In contrast to BODIPY, studies on BOIMPY are still rare.…”

Bis(dioxaborine) Dyes with Variable π‐Bridges: Towards Two‐Photon Absorbing Fluorophores with Very High Brightness

“…[2,[4][5][6] There are several examples of organoboron dyes that fulfill thesei deal requirements to al arge extent. [1,3,[7][8][9][10][11][12][13][14][15][16][17][18][19] An additional asset would be the capacity of dye to be stimulated in at wo-photon excitationp rocess. [20][21][22] This createst he same emissive state as conventional one-photon excitation,b ut makesu se of near-infrared( NIR) photons.…”

“…If these properties are combined with light absorption at wavelengths longer than 400 nm and emission in the spectral region >500 nm, as well as significant Stokes shifts, then dyes with potential in bioimaging or optoelectronic applications are identified . There are several examples of organoboron dyes that fulfill these ideal requirements to a large extent . An additional asset would be the capacity of dye to be stimulated in a two‐photon excitation process .…”