Jean-Charles Vanel

Dependence of the Properties of Dihydroindenofluorene Derivatives on Positional Isomerism: Influence of the Ring Bridging

The future of organic electronics is driven by the synthesis and the study of novel molecular fragments for the construction of highly efficient polymers or oligomers. In this context, polyand oligophenylene derivatives constitute an important class of highly promising molecules, which have been widely studied for the last two decades. Of particular interest in the chemistry and physics of oligophenylenes is the bridged-para-terphenyl unit, namely, 6,12dihydroindeno[1,2-b]fluorene (Scheme 1). Although it has been known since the 1950s, investigations of the dihydroindeno[1,2-b]fluorenyl core only started a decade ago thanks to the pioneering work of M llen, which made this molecule a key building block for electronics. There are nowadays numerous examples of efficient dihydroindeno[1,2-b]fluorenylbased semiconductors that have found application in various fields, such as fluorescent 5–8] and phosphorescent organic light-emitting diodes (OLEDs), organic field-effect transistors, and organic solar cells. This wide range of applications clearly shows the high potential of this building block, but also its versatility. However, the dihydroindeno[1,2-b]fluorene is not the only member of the bridged-terphenyl family, since it possesses four other positional isomers with different phenyl linkages (para/meta/ortho) and different ring-bridging positions (anti vs. syn ; Scheme 1). There are hence five dihydroindenofluorene positional isomers, each possessing its own ring topology, which in turn has structural and electronic consequences. However, in contrast to the dihydroindeno[1,2-b]fluorene, other positional isomers remain very scarce in the literature owing to synthetic difficulties. For example, the dihydroindeno[2,1-a]fluorenyl (syn para-terphenyl) unit (Scheme 1) has only been investigated for organic electronics very recently, and thanks its particular syn geometry has emerged as a promising scaffold for a new generation of excimer-based OLEDs. Similarly, antiaromatic fully conjugated indenofluorene derivatives have recently attracted particular attention; Haley and co-workers have for example reported a new class of (2,1-c)indenofluorenes with high electron affinities. However, the anti and syn meta-terphenyl isomers, that is, dihydroindeno[1,2-a]fluorene and dihydroindeno[2,1-b]fluorene, although known for 60 years, are almost absent from the literature, and their intrinsic properties have never been studied. As the design of novel molecular fragments is of key importance for the future of organic electronics, we report herein the first examples of the use of dihydroindeno[1,2b]fluorene (1) and dihydroindeno[2,1-a]fluorene (2 ; Scheme 1. The five positional dihydroindenofluorene isomers.

Demonstration of full 4×4 Mueller polarimetry through an optical fiber for endoscopic applications.

A novel technique to measure the full 4 × 4 Mueller matrix of a sample through an optical fiber is proposed, opening the way for endoscopic applications of Mueller polarimetry for biomedical diagnosis. The technique is based on two subsequent Mueller matrices measurements: one for characterizing the fiber only, and another for the assembly of fiber and sample. From this differential measurement, we proved theoretically that the polarimetric properties of the sample can be deduced. The proof of principle was experimentally validated by measuring various polarimetric parameters of known optical components. Images of manufactured and biological samples acquired by using this approach are also presented.

Demonstration of Mueller polarimetry through an optical fiber for endoscopic applications

We present very first measurements of Mueller matrices of samples through an optical fiber, opening the way to endoscopic applications for early detection of diseases. The technique is based on measurements of both the single fiber and the assembly fiber+sample Mueller matrices. The 2m optical guide is made of two identical pieces of PM fiber spliced with crossed fast and slow axes in order to (i) minimize residual phase retardance at the output, (ii) and precisely know the eigen axes orientations. Mueller matrices of different calibrated samples are measured, leading to accurate and reliable determination of combined birefringence, diattenuation and depolarization of these samples.

Simple eco-friendly synthesis of the surfactant free SnS nanocrystal toward the photoelectrochemical cell application

A simple, low cost, non-toxic and eco-friendly pathway for synthesizing efficient sunlight-driven tin sulfide photocatalyst was studied. SnS nanocrystals were prepared by using mechanical method. The bulk SnS was obtained by evaporation of SnS nanocrystal solution. The synthesized samples were characterized by using XRD, SEM, TEM, UV-vis, and Raman analyses. Well crystallized SnS nanocrystals were verified and the electrochemical characterization was also performed under visible light irradiation. The SnS nanocrystals have shown remarkable photocurrent density of 7.6 mA cm−2 under 100 mW cm−2 which is about 10 times larger than that of the bulk SnS under notably stable operation conditions. Furthermore, the SnS nanocrystals presented higher stability than the bulk form. The IPCE(Incident photon to current conversion efficiency) of 9.3% at 420 nm was obtained for SnS nanocrystal photoanode which is strikingly higher than that of bulk SnS, 0.78%. This work suggests that the enhancement of reacting area by using SnS nanocrystal absorbers could give rise to the improvement of photoelectrochemical cell efficiency.