Virginia Martínez-Martínez

Modulation of singlet oxygen generation in halogenated BODIPY dyes by substitution at their meso position: towards a solvent-independent standard in the vis region

A series of halogenated BODIPY with different substitutions patterns at meso position such as aryl groups and heteroatoms (methylthio (MeS) and amino (NR2) groups) with various electron-donor and electron-withdrawing properties are studied. A detailed analysis of their photophysical properties as well as a thorough determination of their singlet oxygen quantum yields enlightens the role of the substituents at the meso position. Importantly, one of the new halogenated BODIPY with a methylthio group at the meso position, with intense absorption band in the visible region is proposed as a suitable reference with high singlet oxygen quantum yield, practically constant in different solvents of a wide polarity range.

Distribution and orientation study of dyes intercalated into single sepiolite fibers. A confocal fluorescence microscopy approach

Single sepiolite clay needles doped with dyes of different molecular dimensions, Rhodamine 6G (R6G), Pyronine Y (PY), Styryl 698 (LDS 698) and Styryl 722 (LDS 722), at low and high loadings, are studied by confocal fluorescence microscopy. The combination of fluorescence lifetime imaging (FLIM), polarized fluorescence intensity experiments and spectral resolution shows a straightforward method to study the molecular distribution inside the tunnels and/or at the external channels, the dye orientation (evaluated by the fluorescence dichroic ratio, D) and the formation of different dye species (monomer and aggregates). The ability of the dyes to penetrate into the Sep tunnels is R6G < LDS 698 < PY < LDS 722, analyzed by thermal analysis. As a result the alignment along the main axis of Sep increases in the same order, reaching fluorescence dichroic ratios of around 1.5, 6, 8 and 10 respectively for each dye.

Rational Design of Advanced Photosensitizers Based on Orthogonal BODIPY Dimers to Finely Modulate Singlet Oxygen Generation

The synthesis, photophysical characterization, and modeling of a new library of halogen-free photosensitizers (PS) based on orthogonal boron dipyrromethene (BODIPY) dimers are reported. Herein we establish key structural factors in order to enhance singlet oxygen generation by judiciously choosing the substitution patterns according to key electronic effects and synthetic accessibility factors. The photosensitization mechanism of orthogonal BODIPY dimers is demonstrated to be strongly related to their intrinsic intramolecular charge transfer (ICT) character through the spin-orbit charge-transfer intersystem crossing (SOCT-ISC) mechanism. Thus, singlet oxygen generation can be effectively modulated through the solvent polarity and the presence of electron-donating or withdrawing groups in one of the BODIPY units. The photodynamic therapy (PDT) activity is demonstrated by in vitro experiments, showing that selected photosensitizers are efficiently internalized into HeLa cells, exhibiting low dark toxicity and high phototoxicity, even at low PS concentration (0.05-5×10-6  m).

Enhanced Phosphorescence Emission by Incorporating Aromatic Halides into an Entangled Coordination Framework Based on Naphthalenediimide

Phosphorescence emission at room temperature is turned on in an entangled porous coordination polymer (PCP) with naphthalenediimide (NDI) as chromophore, by incorporating halogenated guests into the pores. The phosphorescent efficiency is drastically increased by the incorporation of aromatic halide guests in comparison with the incorporation of nonaromatic derivatives. Aromatic halide guests trigger a structural transformation, which allows a strong interaction with the NDI ligand in the framework through charge-transfer complexation, and provides an extra population process of the triplet state. The long-lived photoinduced triplet states, with an emission wavelength in the red region of the visible spectrum, demonstrated by this PCP, may open the door for potential uses, for example, as singlet-oxygen generators or for bio-imaging applications.

AcetylacetonateBODIPY-Biscyclometalated Iridium(III) Complexes: Effective Strategy towards Smarter Fluorescent Photosensitizer Agents

Biscyclometalated IrIII complexes involving boron-dipyrromethene (BODIPY)-based ancillary ligands, where the BODIPY unit is grafted to different chelating cores (acetylacetonate for Ir-1 and Ir-2, and bipyridine for Ir-3) by the BODIPY meso position, have been synthesized and characterized. Complexes with the BODIPY moiety directly grafted to acetylacetonate (Ir-1 and Ir-2) exhibit higher absorption coefficients (ϵ≈4.46×104  m-1  cm-1 and 3.38×104  m-1  cm-1 at 517 nm and 594 nm, respectively), higher moderate fluorescence emission (φfl ≈0.08 and 0.22 at 528 nm and 652 nm, respectively) and, in particular, more efficient singlet oxygen generation upon visible-light irradiation (φΔ ≈0.86 and 0.59, respectively) than that exhibited by Ir-3 (φΔ ≈0.51, but only under UV light). Phosphorescence emission, nanosecond time-resolved transient absorption, and DFT calculations suggest that BODIPY-localized long-lived 3 IL states are populated for Ir-1 and Ir-2. In vitro photodynamic therapy (PDT) activity studied for Ir-1 and Ir-2 in HeLa cells shows that such complexes are efficiently internalized into the cells, exhibiting low dark- and high photocytoxicity, even at significantly low complex concentration, making them potentially suitable as theranostic agents.

Formation of a Nonlinear Optical Host-Guest Hybrid Material by Tight Confinement of LDS 722 into Aluminophosphate 1D Nanochannels.

In this work, hemicyanine dye LDS 722 is encapsulated into the 1D elliptical nanochannels of MgAPO-11 aluminophosphate by a crystallization inclusion method. The synthesis of the hybrid material has been optimized through a systematic variation of the crystallization conditions in order to obtain pure and large crystals (around 20 μm×30 μm) suitable for optical applications. The tight fitting between the molecular size of the guest dye and the pore dimensions of the host has favored a rigid planar conformation of the dye, restricting its inherent flexibility, which is confirmed by molecular simulations. Consequently, the encapsulation of LDS 722 into MgAPO-11 has led to an astonishing enhancement of the fluorescence with respect to the dye into MgAPO-5, with slightly larger cylindrical channels, and with respect to the dye in solution. Moreover, the perfect alignment of LDS 722 (dye with intrinsic nonlinear-optical properties) along the channels of MgAPO-11 has revealed attractive second-order nonlinear properties, such as second harmonic generation, proven through microscopy measurements in single crystals.

Preparation, Photophysical Characterization, and Modeling of LDS722/Laponite 2D-Ordered Hybrid Films

A novel hybrid material with promising optical properties for nonlinear optical applications is presented, as formed by LDS 722 organic dye confined in Laponite clay. Thin films of the hybrid material with different dye loadings have been prepared. The film thickness, the dye and water content, and the clay swelling due to guest molecule incorporation have been characterized. Then, the photophysical properties of the thin films have been studied in detail using experimental methods and molecular simulation. As the dye load increases, the hybrid films present a hypsochromic shift in absorption and a bathochromic shift in emission. The former is attributed to the increasing strength of solvation of the dye donor group, while the latter is ascribed to a switch from an intramolecular to an intermolecular charge-transfer process as the dye load increases. The LDS 722 molecules are preferentially oriented in the host clay almost in parallel to the platelet surfaces, inducing macroscopic order that makes the material responsive to polarized light.

Enhanced Charge-Transfer Emission in Polyimides by Cyano-Groups Doping

Conjugated polyimides (PI) are successfully synthesized by chemical imidization through in situ silylation of diamines by the alteration of different donor-acceptor monomers. A detailed photophysical characterization is performed in the monomers and different polymers in tetrahydrofuran solutions. The emission spectra of the related donor-acceptor polymers with electron withdrawing cyano groups showed broader and more intense fluorescence bands in comparison to the polymer without -CN groups. The new emission band results from the contribution of two different charge-transfer (CT) pathways: (i) An intramolecular CT (ICT) state in the donor monomers due to the presence of strong electron withdrawing CN groups, and (ii) a intramolecular CT complex (CTC) in the PI polymer between the donor-acceptor monomers, which is red-shifted and shows longer lifetime respect to the ICT of the diamine monomers. The very wide emission band is a very interesting feature for obtaining white light from UV light.

One-Directional Antenna Systems: Energy Transfer from Monomers to J-Aggregates within 1D Nanoporous Aluminophosphates

A cyanine dye (PIC) was occluded into two 1D-nanopoporus Mg-containing aluminophosphates with different pore size (MgAPO-5 and MgAPO-36 with AFI and ATS zeolitic structure types, with cylindrical channels of 7.3 Å diameter and elliptical channels of 6.7 Å × 7.5 Å, respectively) by crystallization inclusion method. Different J-aggregates are photophysically characterized as a consequence of the different pore size of the MgAPO frameworks, with emission bands at 565 nm and at 610 nm in MgAPO-5 and MgAPO-36, respectively. Computational results indicate a more linear geometry of the J-aggregates inside the nanochannels of the MgAPO-36 sample than those in MgAPO-5, which is as a consequence of the more constrained environment in the former. For the same reason, the fluorescence of the PIC monomers at 550 nm is also activated within the MgAPO-36 channels. Owing to the strategic distribution of the fluorescent PIC species in MgAPO-36 crystals (monomers at one edge and J-aggregates with intriguing emission properties at the other edge) an efficient and one-directional antenna system is obtained. The unidirectional energy transfer process from monomers to J-aggregates is demonstrated by remote excitation experiments along tens of microns of distance.

Singlet Fission Mediated Photophysics of BODIPY Dimers

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.