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Molecular Photonics

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Systems with enhanced two-photon absorption

Remarkable Organic or Organometallic Octupoles.
Isocyanurates functionalized by donor arms at the periphery reveal remarkable NLO properties as octupolar derivatives. In addition to a good activity/transparency trade-off regarding their hyperpolarizabilities, high two-photon absorption (TPA) cross-sections have been evidenced for the extended derivatives.

G. Argouarch, R. Veillard, T. Roisnel, A. Amar, H. Meghezzi, A. Boucekkine, V. Hugues, O. Mongin, M. Blanchard-Desce, F. Paul Chem. Eur. J. 2012, 18, 11811; DOI: 10.1002/chem.201200484.

Moreover, much improved NLO activities can be achieved by replacing peripheral organic electron-releasing phenyl groups by electron-rich organometallics.

A. Trujillo, R. Veillard, G. Argouarch, T. Roisnel, A. Singh, I. Ledoux, F. Paul Dalton Trans. 2012, 41, 7454 ; DOI: 10.1039/C2DT30555K.

Linear Optical and Third-Order Nonlinear Optical Properties of Some Fluorenyl- and Triarylamine-Containing Tetracyanobutadiene Derivatives

A glass of fluorescence! The synthesis and characterization of four new tetracyanobutadiene (TCBD) derivatives incorporating 2- or 2,7-fluorenyl and diphenylamino moieties are reported. The electroactivity was studied by cyclic voltammetry (CV), while the linear optical and (third order) nonlinear optical (NLO) properties were investigated by electronic spectroscopy and Z-scan studies, respectively. All experimental investigations were rationalized by DFT computations, providing an insight into the electronic structure of these derivatives and on their application potential. We show that these derivatives are nonluminescent in solution at ambient temperatures, but become fluorescent in solvent glasses. This finding constitutes an unprecedented observation for TCBD derivatives. Also, we show by Z-scan studies that these derivatives behave as two-photon absorbers in the near-IR range (800–1050 nm). These third-order NLO properties are discussed and compared with those of their alkynyl precursors, which have been investigated by two-photon excited fluorescence (TPEF).

Z. Pokladek, N. Ripoche, M. Betou, Y. Trolez, O. Mongin, J. Olesiak-Banska, K. Matczyszyn, M. Samoc, M. G. Humphrey, M. Blanchard-Desce, F. Paul Chem. Eur. J. 2016, 22, 10155 – 10167; DOI: 10.1002/chem.201600897.

Fluorescent two-photon absorbers for bio-imaging and theranostics

We are also interested in developing two-photon absorbers for applications in bio-imaging, sensing and photodynamic therapy of cancers. The aim is to design (nano)probes and (nano)devices for imaging and/or therapy, by taking advantage of multiphoton excitation, which allows enhanced 3D resolution and penetration depth as well as reduced photodamages in comparison with one-photon excitation.

pKa tuning in quadrupolar-type two-photon ratiometric fluorescent membrane probes

Two bolaamphiphilic quadrupoles built from a fluorene core conjugated with azine endgroups were designed and successfully used to stain GUV membranes. Their quadrupolar character induces both a shift of the pKa values close to physiological pH and large two-photon absorption responses (i.e. over 1000 GM for acidic forms). As such they hold promise as ratiometric two-photon pH probes for monitoring slight variations of pH near cell membranes using two-photon excitation in the NIR region.

J. Daniel, C. Mastrodonato, A. Sourdon, G. Clermont, J.-M. Vabre, B. Goudeau, H. Voldoire, S. Arbault, O. Mongin, M. Blanchard-Desce Chem. Commun. 2015, 51, 15245-15248; DOI: 10.1039/c5cc04573h.

Synthesis and Characterization of new Conjugated Fluorenyl-Porphyrin Dendrimers for Optics

Seeing porphyrins in a new light! A new family of conjugated meso-tetraphenylporphyrin-based dendrimers with four, eight and up to sixteen fluorenyl groups has been synthesized and fully characterized. These tetraphenylporphyrin-cored dendrimers present peripheral alkynyl π-conjugated dendrons with fluorenyl termini. Variations of the position (para or meta) of the dendron branching on the meso-phenyl rings of the TPP core significantly influence the spectroscopic properties of the final porphyrin dendrimers, as well as the number of terminal 2-fluorene groups in each dendron. Energy transfer from the peripheral fluorene-containing antennae to the central porphyrin core is nearly quantitative, regardless of the number of fluorene groups in the peripheral dendrons and of their branching point at the meso-phenyl rings. However, for the para-functionalized series, larger luminescence quantum yields are observed than for the meta-substituted ones. In comparison with reference TPP, both para and meta-substituted compounds exhibit intrinsic two-photon absorption cross-sections enhanced by at least one order of magnitude, together with higher or maintained singlet oxygen quantum yields. Para-substituted dendrimer TPP2 combines the largest enhancements of both two-photon brightness and two-photon singlet oxygen production. Such kind of molecular engineering is therefore also very promising for theranostic applications combining two-photon fluorescence imaging and photodynamic therapy.

D. Yao, X. Zhang, O. Mongin, F. Paul, C. O. Paul-Roth Chem. Eur. J., 2016, 22, 5583-5597; DOI: 10.1002/chem.201504617.

Organometallic porphyrin derivatives

A large improvement in the NLO properties results when simple zinc(II) tetraphenylporphyrins are functionalized by electron-rich metal-alkynyl endgroups at the para positions of their peripheral meso-phenyl groups.

S. Drouet, A. Merhi, G. Grelaud, M. P. Cifuentes, M. G. Humphrey, K. Matczyszyn, M. Samoc, L. Toupet, C. O. Paul-Roth, F. Paul New J. Chem. 2012, 36, 2192; DOI:10.1039/C2NJ40589J.

For instance, molecules exhibiting large effective two photon absorption (TPA) cross-sections in the visible/near-IR range.

Merhi, G. Grelaud, K. A. Green, N. H. Minh, M. Reynolds, I. Ledoux, A. Barlow, G. Wang, M. P. Cifuentes, M. G. Humphrey, F. Paul, C. O. Paul-Roth Dalton Trans. 2015, 44, 7748; DOI: 10.1039/C5DT00768B.

Switchable NLO-phores

Redox-switching between Six States

Modular construction of complexes containing ferrocenyl, bis(bidentate diphosphine)ruthenium and triarylamine units linked through ethynyl groups has afforded species stable in up to six reversibly-interconvertible redox-active states with distinct linear optical properties.

G. Grelaud, M. P. Cifuentes, T. Schwich, G. Argouarch, S. Petrie, R. Stranger, F. Paul and M. G. Humphrey Eur. J. Inorg. Chem. 2012, 1, 65; DOI: 10.1002/ejic.201100747.

Redox-switching between Two States

Organoiron mono- and bi-metallic complexes containing a 2,7-fluorenediyl unit in the bridge exhibit intramolecular electron-delocalization in their mixed-valent state and switchable cubic nonlinear optical properties. Bridge extension results in less efficient molecular wires, but increasingly contrasted nonlinear electrophores.

F. Malvolti, C. Rouxel, G. Grelaud, L. Toupet, T. Roisnel, X. Yang, G. Wang, A. Barlow, F. I. Abdul Razak, R. Stranger, M. P. Cifuentes, M. G. Humphrey, O. Mongin, M. Blanchard-Desce, C. O. Paul-Roth and F. Paul Organometallics 2015, 34, 5418–5437; DOI: 10.1021/ acs.organomet.5b00769.

Redox-switchable Porphyrin-based Dyads

Spectroelectrochemical studies show four accessible redox states on dyad 3 with the first oxidation process taking place at the Ru(II) centre and the second oxidation and first reduction processes at the porphyrin centre.

A. Merhi, X. Zhang, D. Yao, S. Drouet, O. Mongin, F. Paul, J. A. G. Williams, M. A. Fox and C. O. Paul-Roth Dalton Trans. 2015, 44, 9470-9485; DOI: 10.1039/C5DT00348B.