Jorge Bañuelos

Structural, photophysical and lasing properties of pyrromethene dyes

The molecular structure and the photophysical properties of pyrromethene-BF2 (PM) dyes are studied with the aim of finding the best structural and environmental conditions which optimize the laser performance of these dyes. To this end, UV–Vis absorption and fluorescence spectra and fluorescence decay curves of several PM dyes are registered in a multitude of solvents with different physicochemical properties and in polymeric solid matrices. Quantum mechanical calculations at different levels are also applied in order to explain the photophysical behaviour of these dyes. The studied pyrromethenes incorporate alkyl (methyl, ethyl and tert-butyl), sulfonate, cyano, and acetoxy- and methacryloyloxy-polymethylene groups in different positions of the chromophore. In the last case, the presence of the polymerizable acryloyl group facilitates the covalent linkage of the chromophore to a polymeric chain, of special technological interest in the development of tunable dye lasers in the solid state. From the experimental results and the theoretical calculations, we discuss different mechanisms of internal conversion for PM dyes, such as the loss in the planarity of the chromophore, the electron flow through the delocalized π-system, the vibrational coupling and the formation of an intramolecular charge transfer state. The present work demonstrates the good correlation between the photophysical and the lasing properties of PM dyes with different structural (substituents) and environmental (solvents and polymers) conditions. Contents PAGE 1. Introduction 340 2. Methodology 342 2.1. Dyes 342 2.2. Instrumental 344 2.3. Computational 345 3. Results and discussion 346 3.1. Preliminary considerations. Molecular structure 346 3.2. General photophysics 348 3.3. 2,6-Disubstituted-pyrromethenes 351 3.3.1. Solvent e.ect 355 3.3.2. Photophysics-lasing correlations 357 3.3.3. PM567 in polymeric matrices: cross-linking e.ect 357 3.4. Acetoxy-pyrromethenes 360 3.4.1. Linear 8-acetoxy analogues 361 3.4.2. 8-phenyl analogues 363 3.4.3. Solid polymeric matrices 365 3.5. 8-Cyano group: intramolecular charge transfer (ICT) state 367 4. Conclusions 371 Acknowledgements 371 References 372

New 8‐Amino‐BODIPY Derivatives: Surpassing Laser Dyes at Blue‐Edge Wavelengths

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.

8-PropargylaminoBODIPY: unprecedented blue-emitting pyrromethene dye. Synthesis, photophysics and laser properties

Highly emitting 8-propargylaminoBODIPY (8-PAB) 2 was prepared in 94% yield. Unlike any other BODIPY structure hitherto described in the literature, 2 displays efficient emission in the blue region of the visible spectrum with a fluorescence quantum yield up to 0.94 and high laser efficiency (35%) at 483 nm.

BODIPY Dye, the Most Versatile Fluorophore Ever?

BODIPY laser dyes constitute a fascinating topic of research in modern photochemistry due to the large variety of options its chromophore offers, which is ready available for a multitude of synthetic routes. Indeed, in the literature one can find a huge battery of compounds based on the indacene core. The possibility of modulating the spectroscopic properties or inducing new photophysical processes by the substitution pattern of the BODIPY dyes has boosted the number of scientific and technological applications for these fluorophores. Along the following lines, I will overview the main results achieved in our laboratory with BODIPYs oriented to optoelectronic as well to biophotonic applications, stressing the more relevant photophysical issues to be considered in the design of a tailor-made BODIPY for a certain application and pointing out some of the remaining challenges.

8-AminoBODIPYs: Cyanines or Hemicyanines? The Effect of the Coplanarity of the Amino Group on Their Optical Properties

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.

Modulation of the photophysical properties of BODIPY dyes by substitution at their meso position.

We report the photophysical properties of new BODIPY derivatives monosubstituted at the central position. The presence of different functional groups induced the appearance of new photophysical processes in BODIPY dyes, such as intramolecular charge or energy transfer. These phenomena are sensitive to solvent properties (mainly the polarity) and have a potential use as fluorescent probes. Adequate modifications in their molecular structure or in the environment polarity can modulate the emission region of these fluorophores in the visible spectral region. Specifically, different processes and photophysical behaviors can be achieved depending on the excited chromophore and/or the solvent characteristics in a bichromophoric pyrene-BODIPY system.

Blue‐to‐Orange Color‐Tunable Laser Emission from Tailored Boron‐Dipyrromethene Dyes

A series of meso-substituted boron-bipyrromethene (BODIPY) dyes are synthesized and their laser and photophysical properties systematically studied. Laser emission covering a wide visible spectral region (from blue to orange) is obtained by just changing the electron donor character of the heteroatom at position 8. The additional presence of methyl groups at positions 3 and 5 results in dyes with a photostability similar to that of the unsubstituted dye but with much improved efficiency. Correlation of the lasing properties of the different dyes to their photophysical properties provides inklings to define synthetic strategies of new BODIPY dyes with enhanced efficiency and modulated wavelength emission over the visible spectral region.

Near‐IR BODIPY Dyes à la Carte—Programmed Orthogonal Functionalization of Rationally Designed Building Blocks

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 (SN Ar), 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.

Nitro and amino BODIPYS: crucial substituents to modulate their photonic behavior

The present work deals with the synthesis and photophysical, quantum mechanical, and lasing characterization of novel BODIPYs bearing amino and nitro groups at different positions in the core. The results emphasize the relevant role on the photophysical and lasing properties, not only of the attached functionality but also of the position in which is grafted, as well as the molecular structure of the indacene core. A wide part of the visible spectrum can be covered by the insertion of an amino group at position 3 (red shift) or 8 (blue shift). Furthermore, the electron withdrawing character of the nitro substituent induces intramolecular charge transfer processes, the efficiency of which depends on the position of the nitro group on the BODIPY core. All these experimental findings can be rationalized with the help of quantum mechanical calculations.

Selective lateral lithiation of methyl BODIPYs: synthesis, photophysics, and electrochemistry of new meso derivatives.

Selected meso BODIPYs (chemically reactive, difficult to obtain by established procedures, or photophysically or electrochemically attractive) have been obtained by unprecedented selective lateral lithiation of 8-methylBODIPYs. The physical study of the obtained new meso BODIPYs reveals interesting tunable properties related to the activation of intramolecular charge-transfer processes, endorsing the new synthetic methodology as useful for the development of smarter BODIPY dyes for technological applications.