Anthony D'Aléo

Two-photon excited fluorescence of BF2 complexes of curcumin analogues: toward NIR-to-NIR fluorescent organic nanoparticles

The synthesis of borondifluoride complexes of curcuminoids and one- and two-photon absorption properties of 1 and 2 are described. These compounds allow the preparation of organic nanoparticles that were characterized using DLS, TEM and AFM revealing sizes around 50–60 nm for 2. The fluorescence emission spectra of the nanoparticles are red-shifted compared to those of the dye diluted in dichloromethane solution reaching the NIR region of the spectrum. This effect stems from the occurrence of π–π interactions in the solid state, as revealed from the X-ray crystal structure analysis of 1. Those dyes exhibit a significant two-photon absorption cross-section in solution and nanoparticle suspension in water. The nanoparticles are shown to behave as NIR-to-NIR fluorescent nanomaterials that could be potentially used for studies in the biological transparency window. Two-photon brightnesses of ca. 13–14 GM are obtained for both dyes, which are amongst some of the highest values reported to date for NIR-to-NIR luminophores.

11-Aminoundecanoic acid: a versatile unit for the generation of low molecular weight gelators for water and organic solvents

The use of 11-aminoundecanoic acid as a synthetic building-block allows the systematic preparation of (oligo)amide organogelators-including chiral ones-which display remarkable gelation properties in organic solvents and water.

Electronic energy and electron transfer processes in photoexcited donor-acceptor dyad and triad molecular systems based on triphenylene and perylene diimide units.

We investigate the photophysical properties of organic donor-acceptor dyad and triad molecular systems based on triphenylene and perylene diimide units linked by a non-conjugated flexible bridge in solution using complementary optical spectroscopy techniques. When these molecules are diluted in dichloromethane solution, energy transfer from the triphenylene to the perylene diimide excited moieties is evidenced by time-resolved fluorescence measurements resulting in a quenching of the emission from the triphenylene moieties. Simultaneously, another quenching process that affects the emission from both donor and acceptor units is observed. Solution ultrafast transient absorption measurements provide evidence of photo-induced charge transfer from either the donor or the acceptor depending upon the excitation. Overall, the analysis of the detailed time-resolved spectroscopic measurements carried out in the dyad and triad systems as well as in the triphenylene and perylene diimide units alone provides useful information both to better understand the relations between energy and charge transfer processes with molecular structures, and for the design of future functional dyad and triad architectures based on donor and acceptor moieties for organic optoelectronic applications.

meso-Ester Corroles.

The introduction of ester groups on the 5- and 15-meso positions of corroles stabilizes them against oxidation and induces a redshift of their absorption and emission spectra. These effects are studied through the photophysical and electrochemical characterization of up to 16 different 5,15-diester corroles, in which the third meso position is free or occupied by an aryl group, a long alkyl chain, or an ester moiety. Single-crystal X-ray structure analysis of five 5,15-diestercorroles and DFT and time-dependent DFT calculations show that the strong electron-withdrawing character of the 5,15 ester substituents is reinforced by their π overlap with the macrocyclic aromatic system. The crystal packing of corroles 2, 4, 6, 9, and 15 features short distances between chromophores that are stacked into columns thanks to the low steric hindrance of meso-ester groups. This close packing is partially due to intermolecular interactions that involve inner hydrogen and nitrogen atoms, and thereby, stabilize a single, identical corrole tautomeric form.

Influence of the electron donor groups on the optical and electrochemical properties of borondifluoride complexes of curcuminoid derivatives: a joint theoretical and experimental study

Molecules displaying a p-conjugated D–A–D structure, in which D and A are electron donor and acceptor groups, respectively, represent an important class of dyes. In this work, we present a series of borondifluoride complexes of curcuminoid derivatives in which the central dioxaborine ring acts as a strong electron acceptor unit. Compounds 1–15 differ by the nature of the terminal D groups. We have also studied unsymmetrical compounds 16–23 that contain two different terminal donor groups, as well as compounds 24–32 in which an electron acceptor or donor unit has been introduced at the meso position of the dioxaborine ring. We describe the synthesis of the dyes that have not yet been reported in the literature, and report the electrochemical, absorption and fluorescence properties of all the compounds in dichloromethane. To gain insights into the electronic structures and optical properties, we performed DFT/TD-DFT calculations for a panel of representative compounds. We established correlations between the reduction potential and the Hammett s and s + constants, as well as between the redox gap and the emission wavelength. The electron donor character of one terminal D unit strongly influences (88 mV per unit of s) the reduction potential due to the strong resonance interaction along the curcuminoid backbone. The correlation points to the smaller effect of the meso substituent (50 mV per unit of s), which we relate to the twisted ground-state geometry of the meso aryl substituent. The correlation models established in this study may be useful to anticipate the optical and electrochemical properties of borondifluoride complexes of curcuminoids with good reliability.

Theoretical and Experimental Study on Boron β‐Diketonate Complexes with Intense Two‐Photon‐Induced Fluorescence in Solution and in the Solid State

Three boron diketonate chromophores with extended π-conjugated backbone were prepared and their spectroscopic features were investigated through a combined theoretical/experimental study. It was shown that these complexes, which undergo very large electronic reorganization upon photoexcitation, combine large two-photon absorption cross section with an emission energy and quantum efficiency in solution that is strongly dependent on solvent polarity. The strong positive influence of boron complexation on the magnitude of the two-photon absorption was clearly established, and it was shown that the two-photon absorption properties were dominated by the quadrupolar term. For one of the synthesized compounds, intense one- and two-photon-induced solid-state emission (fluorescence quantum yield of 0.65 with maximum wavelength of 610 nm) was obtained as a result of antiparallel J-aggregate crystal packing.

Synthesis, electrochemical and photophysical studies of the borondifluoride complex of a meta-linked biscurcuminoid

The synthesis of the borondifluoride complex of a biscurcuminoid system is described, and its electrochemical and photophysical properties are compared to those of a series of monochromophoric models. The data show that the meta-linked biscurcuminoid exhibits enhanced optical properties in solution, such as high optical brightnesses obtained at one- and two-photon excitation (B1 = 87 000 M−1 cm−1 and B2 = 313 GM, respectively). UV/visible absorption of solid-state particles formed in water solution revealed that the four investigated dyes are strongly aggregated and fluorescence spectroscopy showed that they are emissive in the NIR with fluorescence quantum yields spanning from 1.5 to 12.5%. In the case of the meta-linked biscurcuminoid, a high brightness is obtained using one- and two-photon excitation (B1 = 6952 M−1 cm−1 and B2 = 70 GM, respectively). Such red-shifted emission combined with a yet significant brightness in the solid-state is believed to arise from the choice of the meta-linkage which limits strong intermolecular packing.

Donor–σ–Acceptor Motifs: Thermally Activated Delayed Fluorescence Emitters with Dual Upconversion

A family of organic emitters with a donor-σ-acceptor (D-σ-A) motif is presented. Owing to the weakly coupled D-σ-A intramolecular charge-transfer state, a transition from the localized excited triplet state (3 LE) and charge-transfer triplet state (3 CT) to the charge-transfer singlet state (1 CT) occurred with a small activation energy and high photoluminescence quantum efficiency. Two thermally activated delayed fluorescence (TADF) components were identified, one of which has a very short lifetime of 200-400 ns and the other a longer TADF lifetime of the order of microseconds. In particular, the two D-σ-A materials presented strong blue emission with TADF properties in toluene. These results will shed light on the molecular design of new TADF emitters with short delayed lifetimes.

Salts of 4-Substituted Dipicolinic Acid Derivatives − Very Low Molecular Mass Gelators of Aqueous DMSO

This study reports on the gelation behaviour of a well-known family of dipicolinic acid derivatives that lack any long aliphatic chain as substituent. The mechanism of gelation is likely to arise from the base-assisted deprotonation of the carboxylic functionality which leads to the formation of the

Structure–charge transfer property relationship in self-assembled discotic liquid-crystalline donor–acceptor dyad and triad thin films

The photophysical properties of donor–acceptor (D–A) and donor–acceptor–donor (D–A–D) liquid crystalline dyads and triads based on two different discotic mesogens are examined in thin films by steady-state optical spectroscopy and subpicosecond transient absorption measurements. In these systems, triphenylene and perylene bisimide units are covalently linked by flexible decyloxy chain(s) and act as an electron donor (D) and acceptor (A), respectively. These discotic liquid-crystalline systems form well-separated D and A π-stacked columnar structures in thin films. The absorption spectra of the films indicate an aggregation of the perylene bisimide and triphenylene moieties along the columns. Steady-state photoluminescence measurements show a strong fluorescence quenching that is mainly attributed to a photo-induced charge transfer process taking place between the triphenylene and perylene bisimide units. Subpicosecond transient absorption measurements show that the photoinduced charge transfer (CT) states in the dyad and triad films are formed within 0.3 ps and recombine on a 150–360 ps time scale. In addition, a correlation between the dynamics of the charge recombination process and the spacing distances between D and A units can be established in the dyad and triad films. This study provides important information on the relationship between molecular packing and the charge transfer properties in such self-organized D and A columnar nanostructures.