Maria J. Ortiz

Circularly Polarized Luminescence by Visible-Light Absorption in a Chiral O-BODIPY Dye: Unprecedented Design of CPL Organic Molecules from Achiral Chromophores

Circularly polarized luminescence (CPL) in simple (small, nonaggregated, nonpolymeric) O-BODIPYs (R)-1 and (S)-1 by irradiation with visible light is first detected as proof of the ability of a new structural design to achieve CPL from inherently achiral monochromophore systems in simple organic molecules. The measured level of CPL (|glum|) in solution falls into the usual range of that obtained from other simple organic molecules (10–5–10–2 range), but the latter having more complex architectures since axially chiral chromophores or multichromophore systems are usually required. The new design is based on chirally perturbing the acting achiral chromophore by orthogonally tethering a single axially chiral 1,1′-binaphtyl moiety to it. The latter does not participate as a chromophore in the light-absorption/emission phenomenon. This simple design opens up new perspectives for the future development of new small-sized CPL organic dyes (e.g., those based on other highly luminescent achiral chromophores and/or chirally perturbing moieties), as well as for the improvement of the CPL properties of the organic molecules spanning their use in photonic applications.

First Highly Efficient and Photostable E and C Derivatives of 4,4‐Difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY) as Dye Lasers in the Liquid Phase, Thin Films, and Solid‐State Rods

A new library of E- and C-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivatives has been synthesized through a straightforward protocol from commercially available BODIPY complexes, and a systematic study of the photophysical properties and laser behavior related to the electronic properties of the B-substituent group (alkynyl, cyano, vinyl, aryl, and alkyl) has been carried out. The replacement of fluorine atoms by electron-withdrawing groups enhances the fluorescence response of the dye, whereas electron-donor groups diminish the fluorescence efficiency. As a consequence, these compounds exhibit enhanced laser action with respect to their parent dyes, both in liquid solution and in the solid phase, with lasing efficiencies under transversal pumping up to 73 % in liquid solution and 53 % in a solid matrix. The new dyes also showed enhanced photostability. In a solid matrix, the derivative of commercial dye PM597 that incorporated cyano groups at the boron center exhibited a very high lasing stability, with the laser emission remaining at the initial level after 100 000 pump pulses in the same position of the sample at a 10 Hz repetition rate. Distributed feedback laser emission was demonstrated with organic films that incorporated parent dye PM597 and its cyano derivative. The films were deposited onto quartz substrates engraved with appropriate periodical structures. The C derivative exhibited a laser threshold lower than that of the parent dye as well as lasing intensities up to three orders of magnitude higher.

8-Functionalization of alkyl-substituted-3,8-dimethyl BODIPYs by Knoevenagel condensation.

New 8-alkenylBODIPYs have been synthesized by Knoevenagel condensation between a series of alkyl-substituted-3,8-dimethylBODIPYs and aromatic or aliphatic aldehydes. This is in clear contrast with literature precedents, which indicate that this reaction occurs exclusively on the methyl group at C-3. The change in hybridization of the carbon at the 8-position (from sp(3) to sp(2)) determines the fluorescence emission of the BODIPY, while the presence of electron-donating or -withdrawing groups leads to intramolecular charge transfer processes.

Controlling Optical Properties and Function of BODIPY by Using Asymmetric Substitution Effects

Asymmetrically substituted BODIPY analogues of the dye PM567 have been synthesised from 2-acylpyrroles and pyrroles that bear indene, fluorene or difluorene units. The type of linkage between the fluorene and the BODIPY core plays an important role in the photophysics of the BODIPY chromophore. Indeed, an aliphatic bridge gives rise to an energy-transfer process between the chromophores, whereas a vinyl spacer allows an electronic interaction between them, leading to a large red shift of the spectral bands. The laser action of the new dyes has been analysed under transversal pumping at 10 Hz repetition rate, in both liquid phase and incorporated into solid polymeric matrices. Lasing efficiencies of up to 40% were reached with high photostabilities with the laser output remaining at the initial level after 1×10(5) pump pulses in the same position of the sample. The laser action of the new dyes outperforms the laser behaviour of commercial dyes that emit in the same spectral region. The replacement of fluorene by indene quenches the fluorescence and laser emission, but allows the development of an iron cation fluorescent sensor.

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.

Bis(haloBODIPYs) with Labile Helicity: Valuable Simple Organic Molecules That Enable Circularly Polarized Luminescence

Simple organic molecules (SOM) based on bis(haloBODIPY) are shown to enable circularly polarized luminescence (CPL), giving rise to a new structural design for technologically valuable CPL-SOMs. The established design comprises together synthetic accessibility, labile helicity, possibility of reversing the handedness of the circularly polarized emission, and reactive functional groups, making it unique and attractive as advantageous platform for the development of smart CPL-SOMs.

SmI2-mediated 3-exo-trig cyclization of β,γ-unsaturated carbonyl compounds: diastereoselective synthesis of cyclopropanols.

SmI(2)-mediated 3-exo-trig cyclizations of β,γ-unsaturated carbonyl compounds to generate cyclopropanols are not generally observed processes. The reported examples are limited to β,γ-unsaturated carbonyl compounds that possess ester groups conjugated with the alkene unit. The results of the current study show that this cyclization also occurs when other substitution patterns are present on the alkene moiety, affording (E)-cyclopropanols in good to excellent yields and in most cases with high degrees of diastereoselectivity.

Negishi reaction in BODIPY dyes. Unprecedented alkylation by palladium-catalyzed C–C coupling in boron dipyrromethene derivatives

Negishi reactions of 3-halogen and 3,5-dihalogen substituted BODIPYs with different organozinc reagents are reported as the first examples of this valuable palladium-catalyzed C–C coupling reaction into the family of the BODIPY dyes. It is demonstrated that the Negishi coupling is especially useful for obtaining interesting alkylated BODIPYs, including synthetically-valuable asymmetrically-3,5-disubstituted BODIPYs.

Exploring the Application of the Negishi Reaction of HaloBODIPYs: Generality, Regioselectivity, and Synthetic Utility in the Development of BODIPY Laser Dyes

The generality of the palladium-catalyzed C-C coupling Negishi reaction when applied to haloBODIPYs is demonstrated on the basis of selected starting BODIPYs, including polyhalogenated and/or asymmetrical systems, and organozinc reagents. This reaction is an interesting synthetic tool in BODIPY chemistry, mainly because it allows a valuable regioselective postfunctionalization of BODIPY chromophores with different functional groups. In this way, functional patterns that are difficult to obtain by other procedures (e.g., asymmetrically functionalized BODIPYs involving halogenated positions) can now be made. The regioselectivity is achieved by controlling the reaction conditions and is based on almost-general reactivity preferences, and the nature of the involved halogens and their positions. This ability is exemplified by the preparation of a series of new BODIPY dyes with unprecedented substitution patterns allowing noticeable lasing properties.