A detailed photophysical study was performed on an entangled porous coordination polymer (PCP) containing N,N′-dipyrid-4-yl-1,4,5,8-naphthalenediimide (dpNDI) as an electron acceptor moiety and ...different substituted benzene guests as electron donor units by time-resolved fluorescence spectroscopy. Emission from exciplex (A–D)*EX and charge transfer complex (Aδ−–Dδ+)*CT states was identified thanks to the different conformations adopted by aromatic guests in the different adsorption sites of the PCP (denominated pore A and pore B). Fluorescence lifetime values of exciplexes and charge transfer complexes linearly correlate with the dipole moments and the ionization potentials of different substituted benzene guests, respectively. We have also identified other emissive species with much lower emission efficiency, that is, emission from the NDI pillar itself and from its interaction with the benzenedicarboxylate linker.
Herein, we report the synthesis of polyfunctional BODIPY building blocks suitable to be subjected to several reaction sequences with complete chemoselectivity, thereby allowing the preparation of ...complex BODIPY derivatives in a versatile and programmable manner. The reactions included the Liebeskind–Srogl cross‐coupling reaction (LSCC), nucleophilic aromatic substitution (SNAr), Suzuki, Sonogashira, and Stille couplings, and a desulfitative reduction of the MeS group. This novel synthetic protocol is a powerful route to design a library of compounds with tailored photophysical properties for advanced applications. In this context, it is noteworthy that it offers a straightforward and cost‐effective strategy to shift the BODIPY emission deep into the near‐infrared spectral region while retaining high fluorescence quantum yields as well as highly efficient and stable laser action. These new dyes outperform the lasing behaviour of dyes considered as benchmarks over the red spectral region, overcoming the important drawbacks associated with these commercial laser dyes, namely low absorption at the standard pump wavelengths (355 and 532 nm) and/or poor photostability.
Versatile functionalization of the BODIPY core: The borondipyrromethene (BODIPY) system has been derivatized in a versatile manner through a strategy based on orthogonal reactivity (see figure). This has allowed access to some red/NIR‐emitting dyes with superior properties to current commercial laser dyes.
A series of mono‐ to hexachlorinated BODIPY dyes have been prepared in good to excellent yields through the use of N‐chlorosuccinimide as an inexpensive halogenating reagent. This library of ...chlorinated dyes allowed analysis in detail, from the experimental and theoretical points of view, of the dependency of the photophysical and optical properties of the dyes on the number and positions of the chlorine substituents on their BODIPY cores. Quantum mechanical calculations predict the regioselectivity of the halogenation reaction and explain why some positions are less prone to chlorination. The new chlorinated BODIPYs exhibit enhanced laser action with respect to their non‐halogenated analogues, both in liquid solution and in the solid phase. In addition, chlorination is a facile and essentially costless protocol for overcoming important shortcomings exhibited by commercially available BODIPYs, which should favor their practical applications in optical and sensing fields.
Chlorination is a direct and low‐cost strategy allowing significant enhancement of the optical properties of BODIPY dyes, overcoming some of their most important shortcomings for laser applications such as low absorptions at standard laser pumping wavelengths and/or low photostabilities.
The photodynamics of an orthogonal BODIPY dimer, particularly the formation of triplet states, has been explored by femtosecond and nanosecond transient absorption measurements. The short time scale ...data show the appearance of transient features of triplet character that, according to quantitative analysis of their intensities, account for more than 100% of the initially excited molecules, which reveals the occurrence of a singlet fission process in the isolated dimers. The formation rate of the triplet correlated state 1(TT) is found to depend on the solvent polarity, pointing to the mediation of a charge transfer character state. The dissociation of the 1(TT) state into pairs of individual triplets determines the triplet yield measured in the long time scales. The kinetic model derived from the results provides a comprehensive view of the photodynamics of BODIPY dimers and permits rationalization of the photophysical parameters of these systems.
We took advantage of the chemoselective meso-functionalization of 2,3,5,6-tetrabromo-8-methylthioBODIPY 6 to prepare a series of 2,3,5,6-tetrabromo-8-arylBODIPY derivatives suitable for SNAr ...substitution reactions with phenols exclusively at positions 3 and 5. Pd(0)-catalyzed intramolecular arylation reaction ensued on the remaining brominated positions 2 and 6 to give a new family of benzofuran-fused BODIPY dyes. This method utilizes readily available starting materials and allows for the preparation of the title compounds with excellent functional group tolerance. Moreover, it was demonstrated that the methodology described herein is amenable for the incorporation of biomolecules. The photophysical and lasing properties of the benzofuran-fused BODIPY dyes were thoroughly analyzed with the aid of electrochemical measurements and quantum mechanical simulations. These dyes show bright and intriguing emission (both fluorescence and laser) toward the red edge of the visible spectrum with remarkable tolerance under strong and continuous irradiation.
The development of highly efficient and stable blue‐emitting dyes to overcome some of the most important shortcomings of available chromophores is of great technological importance for modern ...optical, analytical, electronic, and biological applications. Here, we report the design, synthesis and characterization of new tailor‐made BODIPY dyes with efficient absorption and emission in the blue spectral region. The major challenge is the effective management of the electron‐donor strength of the substitution pattern, in order to modulate the emission of these novel dyes over a wide spectral range (430–500 nm). A direct relationship between the electron‐donor character of the substituent and the extension of the spectral hypsochromic shift is seen through the energy increase of the LUMO state. However, when the electron‐donor character of the substituent is high enough, an intramolecular charge‐transfer process appears to decrease the fluorescence ability of these dyes, especially in polar media. Some of the reported novel BODIPY dyes provide very high fluorescence quantum yields, close to unity, and large Stokes shifts, leading to highly efficient tunable dye lasers in the blue part of the spectrum; this so far remains an unexploited region with BODIPYs. In fact, under demanding transversal pumping conditions, the new dyes lase with unexpectedly high lasing efficiencies of up to 63 %, and also show high photostabilities, outperforming the laser action of other dyes considered as benchmarks in the same spectral region. Considering the easy synthetic protocol and the wide variety of possible substituents, we are confident that this strategy could be successfully extended for the development of efficient blue‐edge emitting materials and devices, impelling biophotonic and optoelectronic applications.
So simple, so efficient, and so blue: 8‐Amino‐BODIPY dyes were prepared in a straightforward and efficient fashion (up to 95 % yield). They emit in the blue spectral region (see figure) with ϕ values up to 1.00, high laser efficiencies (up to 62 %), and good photostabilities. These results demonstrate that these new tailor‐made chromophores can overcome some of the shortcomings of commercial blue‐emitting dyes.
The role of the amino group twisting ability in the BODIPY photophysics for nonsterically hindered and constrained molecular structures was studied. When a coplanar disposition of the amino and the ...BODIPY core is feasible, a hemicyanine-like delocalized π-system gives rise to novel blue and efficient BODIPY laser dyes. The key role of such rotamer is confirmed by newly synthesized derivatives where the amino and the BODIPY core are electronically decoupled by steric repulsions.
In order to elaborate organized two-dimensional arrangements of fluorescent dyes in host solid layered materials, rhodamine 6G (R6G) is encapsulated in supported thin films of laponite (Lap) clay. ...Clay films are elaborated by the spin-coating technique and their surface morphology is analyzed by scanning electron (SEM) and atomic force (AFM) microscopies. The internal order of the stacked clay layers is checked by X-ray diffraction technique (DRX). The thermostability of R6G in the Lap films is discussed on the basis of several thermogravimetric and calorimetric techniques (TG, DTA and DSC). The R6G adsorbed species in Lap films are characterized by absorption and fluorescence (steady-state and time-resolved) spectroscopies. Monomers, dimers and higher-order aggregates are identified for very low (<0.1%), moderate (1–25%) and high (>40% of the total cation exchange capacity, CEC, of the clay) dye content, respectively. Both non-fluorescence H-type and fluorescent J-type aggregates of R6G in Lap films are characterized.
Absorption and fluorescence techniques with linearly polarized light are applied to evaluate the anisotropic photoresponse of R6G in Lap films, from which the preferential orientation of dye molecules with respect to the clay layers can be evaluated. The validity of the newly established fluorescence polarization is contrasted with the well-established absorption polarization method, and the emission spectroscopy with linearly polarized light can be applied to establish the preferential orientation of fluorophore molecular probes incorporated in any rigid and ordered 2D host materials, including monolayers and biological membranes.
Functionalized fluorescent silica nanoparticles were designed and synthesized to selectively target cancer cells for bioimaging analysis. The synthesis method and characterization of functionalized ...fluorescent silica nanoparticles (50-60 nm), as well as internalization and subcellular localization in HeLa cells is reported here. The dye, rhodamine 101 (R101) was physically embedded during the sol-gel synthesis. The dye loading was optimized by varying the synthesis conditions (temperature and dye concentration added to the gel) and by the use of different organotriethoxysilanes as a second silica precursor. Additionally, R101, was also covalently bound to the functionalized external surface of the silica nanoparticles. The quantum yields of the dye-doped silica nanoparticles range from 0.25 to 0.50 and demonstrated an enhanced brightness of 230-260 fold respect to the free dye in solution. The shell of the nanoparticles was further decorated with PEG of 2000 Da and folic acid (FA) to ensure good stability in water and to enhance selectivity to cancer cells, respectively. In vitro assays with HeLa cells showed that fluorescent nanoparticles were internalized by cells accumulating exclusively into lysosomes. Quantitative analysis showed a significantly higher accumulation of FA functionalized fluorescent silica nanoparticles compared to nanoparticles without FA, proving that the former may represent good candidates for targeting cancer cells.
The versatility in the synthesis of BODIPY derivatives in terms of functionalization is further demonstrated. In particular, in this work β–β′-BODIPY dimers with varied functional groups in the meso ...positions were synthesized in very efficient yields and short reaction times from a single platform. A photophysical study was carried out in all of the compounds. The resultant dimers show absorption bands at around 600 nm as a consequence of electronically coupled monomers disposed with a dihedral angle of around 30°, which is supported by theoretical simulations. The emission properties of these molecules are distinguished by the appearance of an ICT state as the polarity of the solvent increases.
PDF
