A study of the amplified spontaneous emission (ASE) properties of three bisfluorene-cored dendrimers in the solid state is reported. The results show that the dendron type has a strong impact on the photoluminescence quantum yield and affects the ASE threshold, the optical gain, and loss coefficients. Optically pumped distributed feedback lasers operating in the blue spectral region were fabricated by spin coating the dendrimer films on top of a two-dimensional corrugated fused silica substrate. A best lasing threshold of 4.5μJ∕cm2 and a slope efficiency of 8.3% were obtained, which demonstrate the high potential of these materials for laser applications.

Color information is much less useful to machine vision systems than to people because the spectrum of light illuminating a scene is unknown. For scenes illuminated by daylight, color information can be made significantly more useful to machine vision systems if the scene is imaged using sensors with a specifically chosen combination of spectral responses. In this paper we show that detectors with a full width at half maximum of up to 100 nm can give good color discrimination, and that conjugated dendrimer chromophores have the spectral properties required to allow machine vision systems to confidently use color information.

One-electron reduction inverts the helicity of copper complexes formed from derivatives of S-methylcysteine and methioninol. The change in conformation of the organic ligand is followed in the exciton-coupled circular dichroism (ECCD) spectra of the complexes.

There has been a great interest in recent years in organic nonlinear optical materials for their applications in photonics and optoelectronics. In particular, materials displaying twophoton absorption and efficient two-photon fluorescence are attractive for applications such as optical limiting, [1,2] optical data storage, [3] two-photon fluorescence microscopy, [4] and two-photon pumped lasing.[5] Two-photon pumped lasing is of increasing interest for making smaller, simpler and cheaper visible laser systems, as the gain medium can be pumped at red or near-infrared wavelengths for which laser diodes are inexpensive and more powerful than lasers needed for single-photon pumping. In addition, as the gain medium can be optically pumped at a wavelength longer than that of the laser emission, there is potential to increase the lifetime and photostability of the material.[6] Two-photon pumped lasing in organic small molecules has been demonstrated in the past in dye solutions [7,8] as well as in dye-doped organogels [9] and dye-doped polymer films.[10]In this context, organic semiconductors emerge as attractive candidates, owing to their high gain coefficients, low concentration quenching and optical losses, and ease of processing. [11][12][13] In addition, large molecules with delocalized electrons can display substantial optical nonlinearities and these properties can be further enhanced and tuned by means of synthetic chemistry. [14][15][16] Among these organic materials, conjugated dendrimers are a special category of organic semiconductors where different properties can be assigned to different parts of the macromolecule, allowing for greater flexibility in the design of materials with specific properties.[17]These molecules commonly consist of a central core containing a conjugated chromophore that determines the optical and electronic properties, a number of dendrons branching out of the core that control the intermolecular interactions and a set of surface groups that control the solubility of the molecule. [18][19][20] Changing any of these properties only requires change of part of the structure, which increases the flexibility for tailoring the materials to particular applications. In addition, they are highly processable from solution, meaning that thin films can be deposited onto various substrates by simple techniques such as spin-coating, allowing for an easy and cost-effective integration into devices. Dendrimers have previously shown great potential for use as gain media in lasers [21,22] and have also been studied in the context of nonlinear absorption, for which the effects of the excited state delocalization and the generation of the dendrimer on the nonlinear optical properties were investigated. [23,24] In this Communication, we report on the study of two-photon absorption and photoluminescence properties of a series of first-generation blue-emitting bisfluorene-cored dendrimers. We show that by adding suitable dendrons we may substantially increase the two-photon absorption while not strongly af...

Two-dimensional distributed feedback lasers using a broadband, red polyfluorene gain mediumWe report the trace vapor detection of the molecule 1,4-dinitrobenzene, a model analyte for the explosive substance 2,4,6-trinitrotoluene, via fluoresence quenching of a first generation conjugated dendrimer containing a 2 , 2Ј-bis͓9,9-di-n-hexylfluorene͔ core. We show that much greater sensitivity can be obtained by using the material as a surface emitting distributed feedback laser. We find that the slope efficiency of the laser is a convenient and sensitive indicator of the presence of the analyte. The slope efficiency decreases by a factor 50 in the presence of 1,4-dinitrobenzene.