Engineering a twist in 9,10-diethynylanthracenes by steric interactions.

A series of 9,10-bis(phenylethynyl)anthracenes decorated with sterically demanding tert-butyl substituents have been prepared and spectroscopically characterised. We demonstrate that the introduction of two bulky substituents in the ortho position of the phenyl rings effectively locks the ground state into a conformation in which the three rings are orthogonal. Fluorescence spectroscopy reveals evidence for partial planarisation of this compound in the excited state at ambient temperature, but this is prevented in low temperature solvent glasses.

Preparation of ordered films containing a phenylene ethynylene oligomer by the Langmuir-Blodgett technique.

This paper reports the fabrication and characterization of Langmuir and Langmuir-Blodgett (LB) films incorporating an oligo(phenylene-ethynylene) (OPE) derivative, namely, 4-[4-(4-hexyloxyphenylethynyl)-phenylethynyl]-benzoic acid (HBPEB). Conditions appropriate for deposition of monolayers of HBPEB at the air-water interface have been established and the resulting Langmuir films characterized by a combination of surface pressure and surface potential versus area per molecule isotherms, Brewster angle microscopy, and ultraviolet reflection spectroscopy. The Langmuir films are readily transferred onto solid substrates, and one-layer LB films transferred at several surface pressures onto mica substrates have been analyzed by means of atomic force microscopy, from which it can be concluded that 14 mN/m is an optimum surface pressure of transference, giving well-ordered homogeneous films without three-dimensional defects and a low surface roughness.

Synthesis, fluorescence, and two-photon absorption of a series of elongated rodlike and banana-shaped quadrupolar fluorophores: a comprehensive study of structure-property relationships.

An extensive series of push-push and pull-pull derivatives was prepared from the symmetrical functionalization of an ambivalent core with conjugated rods made from arylene-vinylene or arylene-ethynylene building blocks, bearing different acceptor or donor end-groups. Their absorption and photoluminescence, as well as their two-photon-absorption (TPA) properties in the near infrared (NIR) region, were systematically investigated to derive structure-property relationships and to lay the guidelines for both spectral tuning and amplification of molecular TPA in the target region. Whatever the nature of the core or of the connectors, push-push systems were found to be more efficient than pull-pull systems, and planarization of the core (fluorene versus biphenyl) always leads to an increase in the TPA cross sections.

Effects of (multi)branching of dipolar chromophores on photophysical properties and two-photon absorption.

To investigate the effect of branching on linear and nonlinear optical properties, a specific series of chromophores, epitome of (multi)branched dipoles, has been thoroughly explored by a combined theoretical and experimental approach. Excited-state structure calculations based on quantum-chemical techniques (time-dependent density functional theory) as well as a Frenkel exciton model nicely complement experimental photoluminescence and one- and two-photon absorption findings and contribute to their interpretation. This allowed us to get a deep insight into the nature of fundamental excited-state dynamics and the nonlinear optical (NLO) response involved.

Absolute measurements of photoluminescence quantum yields of solutions using an integrating sphere.

We demonstrate that absolute measurements of the photoluminescence quantum yield of solutions can be made using an integrating sphere and a conventional fluorimeter. With this method the need for measurements against a luminescence standard is overcome. The sphere is mounted inside a commercial fluorimeter, which gives flexibility in excitation and emission wavelength ranges.

Optical properties of donor-acceptor phenylene-ethynylene systems containing the 6-methylpyran-2-one group as an acceptor.

Donor-acceptor phenylene ethynylene systems containing the 6-methylpyran-2-one group, synthesized via classic or microwave-assisted Sonogashira cross-coupling, exhibit pronounced solvatochromism in fluorescence suggesting a highly polar excited state; 4-[4-(4-N,N-dihexylaminophenylethynyl)phenylethynyl]-6-methylpyran-2-one has a fluorescence quantum yield >0.9 in cyclohexane.

Investigation of two-photon absorption behavior in symmetrical acceptor-pi-acceptor derivatives with dimesitylboryl end-groups. Evidence of new engineering routes for TPA/transparency trade-off optimization.

Investigations of the non-linear optical properties of a novel series of A-pi-A quadrupoles, based on dimesitylboron end-groups, reveal the promising potential of elongated vinylboranes derivatives for combined enhanced two-photon absorption cross-section and improved transparency in the visible region. In addition, the excited state lifetime can be significantly enhanced in A-pi-A'-pi-A derivatives. This opens a new route towards optimized molecules for optical power limiting.

Enhanced two-photon absorption with novel octupolar propeller-shaped fluorophores derived from triphenylamine.

[structure: see text] Novel octupolar fluorophores derived from the symmetrical functionalization of a triphenylamine core with strong acceptor peripheral groups via phenylene-ethynylene linkers have been synthesized and shown to exhibit high fluorescence quantum yields, very large TPA cross-sections in the red-NIR region, and suitable photostability.

Synthesis and photophysical properties of new conjugated fluorophores designed for two-photon-excited fluorescence.

[structure: see text] Novel elongated push-push fluorophores (e.g., 9) were synthesized by 2-fold Sonogashira or Wittigminus signHorner reactions.