Synthesis, Fluorescence and Two-Photon Absorption Properties of Multichromophoric Boron-Dipyrromethene Fluorophores for Two-Photon-Excited Fluorescence Applications

International audienceThe synthesis and the characterization of new multichromophoric boron-dipyrromethene dyes are described. Their absorption, photoluminescence as well as their two-photon absorption properties have been investigated. This work shows that assembling several dyes in conjugated multichromophoric structures is a promising strategy for improving the two-photon absorption properties of such fluorophores in the NIR region while retaining their excellent photoluminescence properties

Two-photon Absorption Engineering of 5-(Fluorenyl)-1,10-phenanthroline-based Ru(II) Complexes

International audienceThis study deals with the fine tuning of the photophysical characteristics, and especially two-photon absorption (2PA) properties, of several homo- and heteroleptic ruthenium(II) complexes involving 5-substituted-1,10-phenanthroline ligands. The 2PA spectra of the complexes were determined in the 700-930 nm range by investigating their two-photon excited luminescence (2PEL). Structure - linear and nonlinear optical properties correlations are discussed, and potential applications (therapy and optical power limiting in the near infrared) can be anticipated

Strong enhancement of two-photon absorption properties in synergic 'semi-disconnected' multiporphyrin assemblies designed for combined imaging and photodynamic therapy.

International audienceThe synthesis and photophysical properties of new multiporphyrin assemblies are described. Their design, based on a smooth electronic disconnection between two-photon absorbing (2PA) octupolar or quadrupolar cores and the peripheral porphyrins, leads to a major increase in (non-resonant) 2PA responses in the NIR, while fully retaining the fluorescence and photosensitization properties of isolated porphyrins. This approach, which involves electronic coupling of semi-disconnected moieties in the higher excited states of the synergic systems, is of interest to fully benefit from the advantages of selective 2PA for application in combined two-photon high resolution imaging and photodynamic therapy

Effects of dipolar interactions on linear and nonlinear optical properties of multichromophore assemblies: A case study

Claudine Katan ‘s present address : CNRS UMR6082 FOTON, INSA de Rennes, 20 avenue des Buttes de Coësmes, CS 70839, 35708 RENNES cedex 7, FranceInternational audienceInterchromophore interactions in flexible multidipolar structures for nonlinear optics were addressed by a combined experimental and theoretical study on two series of one-, two-, and three-chromophore systems in which identical push-pull chromophores are assembled through covalent and flexible linkers in close proximity. The photophysical and nonlinear optical properties (quadratic hyperpolarizability) of the multichromophore systems were investigated and compared to those of the monomeric chromophores. Multimers have larger dipole moments than their monomeric analogues, that is, the dipolar subchromophores self-orientate within the multimeric structures. This effect was found to depend on the intersubchromophore distance in a nontrivial manner, which confirms that molecular engineering of such flexible systems is more complex than in completely geometrically controlled systems. Electric-field-induced second-harmonic generation (EFISHG) measurements in solution revealed increased figures of merit as compared to the monomeric analogue. This effect increases with increasing number and polarity of the individual subchromophores in the nanoassembly and increasing spacing between dipolar subchromophores. Experimental results are interpreted by a theoretical model for interacting polar and polarizable chromophores. The properties of multidipolar assemblies are shown to be related to the relative orientation of chromophores, which is imposed by interchromophore interactions. The supramolecular structure is thus a result of self-organization. The proposed theoretical model was also used to predict the properties of multichromophore structures made up of more polar and polarizable push-pull chromophores, and showed that stronger interchromophore interactions can heavily affect the individual optical responses. This suggests new routes for engineering highly NLO responsive multichromophore systems

Improved Transparency-Nonlinearity Trade-Off with Boroxine-Based Octupolar Molecules

C. Katan present address: CNRS UMR6082 FOTON, INSA de Rennes, 20 avenue des Buttes de Coësmes, CS 70839, 35708 RENNES cedex 7, FranceInternational audienceOver the last two decades, a substantial effort has been devoted to the design of molecules with enhanced NLO responses. It has become increasingly clear over recent years that multipolar structures offer challenging possibilities in this respect. In particular, the octupolar framework provides an interesting route towards enhanced NLO responses and improved nonlinearity-transparency trade-off. In this perspective, we have implemented an innovative route based on octupolar structures derived from the boroxine ring. By grafting three electron-donating appendices on the electron-deficient boroxine core, octupolar quasi-planar molecules displaying markedly improved nonlinearity-transparency trade-off, as compared to the prototypical octupole (TATB) or the extensively studied triazine derivatives, were designed. This route indeed led to octupolar molecules showing (0) values (from calculations and solution measurements) larger than that of TIATB while remaining blue-shifted by nearly 100 nm and totally transparent in the visible region. Combined experimental and theoretical investigations reveal that this behavior is related to a periphery-to-core intramolecular charge transfer phenomenon in relation with the low-aromaticity and electron-withdrawing character of the boroxine ring. This study opens a new route for molecular engineering of transparent octupolar derivatives for NLO, including the design of effective materials for SHG in the visible-blue regio

Dendritic molecular assemblies for singlet oxygen generation: meso-tetraphenylporphyrin-based biphotonic sensitizers with remarkable luminescence

International audienceFour new TPP-based chromophores (1-4) peripherally functionalized with dendrons contg. 2-fluorenyl groups were studied for their potential to serve in photodynamic therapy. Their linear and nonlinear optical properties were investigated. With significant TPA cross-sections at 790 nm, good singlet oxygen generation capabilities and relatively large intrinsic fluorescence, sensitizers such as 1 might become particularly appealing for theranostics

Optical electron transfer through 2,7-diethynylfluorene spacers in mixed-valent complexes containing electron-rich "(η2-dppe)(η5-C5Me5)Fe" endgroups.

International audienceWe report in this communication the study of the intramolecular electron transfer through a 2,7-diethynylfluorenyl spacer in the Fe(II)/Fe(III) mixed-valent (MV) complex [(η(2)-dppe)(η(5)-C(5)Me(5))FeC≡C(2,7-C(21)H(24))C≡CFe(η(5)-C(5)Me(5))(η(2)-dppe)][PF(6)] (1[PF(6)]). The complex is generated in situ by comproportionation from its homovalent dinuclear Fe(II) and Fe(III) parents (1 and 1[PF(6)](2)). It is shown that electronic delocalization is much more effective through a 2,7-fluorenyl than through a 4,4'-biphenyl bridging unit

Ultra-sensitive and selective Hg2+ chemosensors derived from substituted 8-hydroxyquinoline analogues

International audienceNovel analogues of 8-hydroxyquinoline with phosphinate or thiophosphinate functions and styryl fluorophores in the para position to the nitrogen atom were prepared via multi-step syntheses, using phosphorylation and Wittig coupling reactions. A strong affinity between the quinoline analogues and heavy metal ions such as Pb2+, Cd2+ and Hg2+ was highlighted. The interaction of the metal ions with the nitrogen of the styrylquinoline leads to a large red shift of the absorption and emission spectra in agreement with an increase of the photoinduced charge transfer character of the styryl fluorophore. In the presence of metal ions the appearance of a green fluorescence emission is also observed upon excitation at 420 nm or 840 nm, thanks to a significant increase of the two-photon response. Under optimal conditions, a mercury concentration of 15 ppt in a partially aqueous medium can be detected using the thiophosphinate derivative without interference from other metal ions

Addressing charge‐transfer and locally‐excited states in a twisted biphenyl push‐pull chromophore

We present the synthesis and spectroscopic characterization of a twisted push‐pull biphenyl molecule undergoing photoinduced electron transfer. Steady‐state and transient absorption spectra suggest, in this rigid molecular structure, a subtle interplay between locally‐excited and charge‐transfer states, whose equilibrium and dynamics is only driven by solvation. A theoretical model is presented for the solvation dynamics and, with the support of quantum chemical calculations, we demonstrate the existence of two sets of states, having either local or charge‐transfer character, that only “communicate” thanks to solvation, which is the sole driving force for the charge‐separation process