Enhanced Two‐Photon Absorption of Organic Chromophores: Theoretical and Experimental Assessments

Functional organic materials with enhanced two‐photon absorption lead to new technologies in the fields of chemistry, biology, and photonics. In this article we review experimental and theoretical methodologies allowing detailed investigation and analysis of two‐photon absorption properties of organic chromophores. This includes femtosecond two‐photon excited fluorescence experimental setups and quantum‐chemical methodologies based on time‐dependent density functional theory. We thoroughly analyze physical phenomena and trends leading to large two‐photon absorption responses of a few series of model chromophores focusing on the effects of symmetric and asymmetric donor/acceptor substitution and branching.     

Inside Front Cover: An Ultraviolet Organic Thin‐Film Solid‐State Laser for Biomarker Applications (Adv. Mater. 1/2005)

Thin‐film organic solid‐state lasers operating in the ultraviolet wavelength region are fabricated using a novel spiro‐linked material as active organic layer in an optically pumped distributed feedback (DFB) structure in work reported by Riedl and co‐workers on p. 31. The laser wavelength is tunable between 377.7 nm and 395 nm, the shortest laser wavelength reported so far for thin‐film organic solid‐state lasers. The lasers' suitability for spectroscopic applications was tested by use as an excitation source for solutions containing the common fluorescent dyes Coumarin 6, Coumarin 152, and Rhodamine 6G.     

Inside Front Cover: Excimer‐Based White Phosphorescent Organic Light‐Emitting Diodes with Nearly 100 % Internal Quantum Efficiency (Adv. Mater. 2/2007)

By combining the monomer and excimer/aggregate emission of FPt, a white OLED can be obtained. Incorporating the novel host material 26mCPy and engineering the charge balance properties, Jabbour and co‐workers used FPt to demonstrate, for the first time, nearly 100% internal quantum efficiency in white OLEDs (as shown in the image). The work is reported on p. 197.     

Inside Front Cover: Polarized‐Light‐Emitting Quantum‐Rod Diodes (Adv. Mater. 11/2005)

Polarized‐light‐emitting quantum‐rod diodes have been successfully produced using thin layers of quantum rods oriented by a rubbing technique, as shown on the inside cover. Hikmet and co‐workers report on p. 1436 that diode emission at 620 nm with a luminance efficiency of 0.65 cd A^–1 and an external quantum efficiency of 0.49 % is obtained. Light emitted polarized parallel to the long axis of the rods is 1.5 times more intense than that polarized perpendicular to the rods.     

Inside Front Cover: Plasma‐Assisted Synthesis of Silicon Nanocrystal Inks (Adv. Mater. 18/2007)

The inside cover shows a photo and a schematic of a two‐step nonthermal plasma process used to produced silicon nanocrystal inks, that is, stable colloidal solutions of silicon nanocrystals. In the first (upper) plasma, nanocrystals are formed through plasma‐induced dissociation of silane molecules, leading to nanocrystal nucleation through chemical clustering. In the second (lower) plasma step, organic ligands are attached in‐flight to the silicon nanocrystal surfaces. The collected powder of surface functionalized silicon nanocrystals readily forms stable colloidal solutions in nonpolar solvents, report Lorenzo Mangolini and Uwe Kortshagen on p. 2513.     

Inside Front Cover: Field‐Driven Biofunctionalization of Polymer Fiber Surfaces during Electrospinning (Adv. Mater. 1/2007)

Surface‐biofunctionalized synthetic polymer fibers composed of a fiber‐forming host polymer and an oligopeptide conjugate can be prepared from electrospinning, report Spontak and co‐workers on p. 87. The conjugate consists of a polypeptide segment and a polymer block that is compatible with the host polymer. Because the more polarizable peptide segment migrates to the surface during electrospinning, peptide surface‐enrichment is achieved in a single step without further treatment.     

Inside Front Cover: Controlling Morphology in Polymer–Fullerene Mixtures (Adv. Mater. 2/2008)

On p. 240, Klaus Meerholz and co‐workers show control over the aggregation of P3HT in solution by mixing a dipolar, but miscible solvent to the coating solution. The resulting nanoparticle dispersions are stable and allow a quantitative comparison of the absorption spectra of amorphous and aggregated P3HT. These results are interesting not only because they allow control of morphology on the nanometer scale, but they also show a path to low‐cost morphological control of large‐area films, which is an essential step for the commercialization of plastic PV devices.     

Inside Front Cover: Topological Transformation of Vesicular Mesostructured Silica (Adv. Mater. 5/2005)

The micrometer‐scale self‐assembly behavior of MCM‐41‐type mesostructured silica is shown by Tang and co‐workers on p. 578 through study of a family of vesicular mesostructured silica with topology genera from 1 to 0. The inside cover shows a series of typical vesicular structures with different topologies on the micrometer scale. A better understanding of the micrometer‐scale self‐assembly behavior provides a guide for the rational design of new hierarchical organic–inorganic composite materials, and may also shed new light on the natural biosilicification process.