Laurent Galmiche

Preparations and Characterizations of Luminescent Two Dimensional Organic-inorganic Perovskite Semiconductors

This article reviews the synthesis, structural and optical characterizations of some novel luminescent two dimensional organic-inorganic perovskite (2DOIP) semiconductors. These 2DOIP semiconductors show a self-assembled nano-layered structure, having the electronic structure of multi-quantum wells. 2DOIP thin layers and nanoparticles have been prepared through different methods. The structures of the 2DOIP semiconductors are characterized by atomic force microscopy and X-ray diffraction. The optical properties of the 2DOIP semiconductors are characterized from absorption and photoluminescence spectra measured at room and low temperatures. Influences of different components, in particular the organic parts, on the structural and optical properties of the 2DOIP semiconductors are discussed.

Lumicyano™: A new fluorescent cyanoacrylate for a one-step luminescent latent fingermark development

Latent fingermarks developed by cyanoacrylate fuming often lack contrast; therefore further enhancement is required, such as dye staining. This second step is part of the conventional detection sequences performed by forensics practitioners. Dye-staining or powder dusting aims at improving contrast and at increasing the legibility of details, yet their use may at times be limited. Indeed powder dusting may not be effective due to unexpected adherence to the background, and poor affinity to the cyanoacrylate. In the same way staining processes can dye a whole semi-porous surface or may wash the marks. To avoid that second step, a new luminescent cyanoacrylate (Lumicyano™) which allows one-step development without changing the fuming chamber settings (80% humidity rate, 120°C fuming temperature) was developed and assessed. This study aimed at comparing Lumicyano™ to a conventional two-step process. A detailed sensitivity study was conducted on glass slides, as well as the processing of various non-porous and semi-porous substrates, usually considered as problematic for a dye staining step. The results indicate that Lumicyano™ detects fingermarks with equal or better sensitivity and ridge details than currently used cyanoacrylate. Secondly in luminescent mode, good ridges clarity and excellent contrast are observed, even if Lumicyano™ is sometimes less bright than the two-step process. Furthermore, conventional enhancement can still be carried out if needed. As a conclusion, Lumicyano™ makes it possible to avoid an enhancement step which can be detrimental to further examinations, particularly on rough or semi-porous surfaces.

Synthesis and optical properties of novel organic–inorganic hybrid UV (R–NH3)2PbCl4 semiconductors

We report on the synthesis and the optical properties of several novel ultraviolet (UV) semiconductors (R–NH3)2PbCl4. These semiconductors are two dimensional organic–inorganic perovskite (2DOIP) materials and have multiple quantum-well energy level structures. We systematically varied the organic components (R–NH3+), and discussed their influence on the self-organization ability, excitonic optical features, and long-term photo-stabilities of the 2DOIPs. The trends of selecting the organic groups to tailor the optical features and to improve the self-organization and long-term photo-stabilities of 2DOIPs are obtained by analyzing the experimental results. Self-organization abilities are found to be highly dependent on the interactions among the organic components. The excitonic optical properties of 2DOIPs are found to depend more on the steric structures, and less on the electronic structures and chemical properties of the organic groups (R–NH2) as long as the organic groups are optically inert. However, the long-term photo-stabilities of the (R–NH3)2PbCl4 semiconductors are highly dependent on the thermal and photo stabilities of organic components. We find a new UV semiconductor, (C6H11CH2NH3)2PbCl4 (CMPC), which has better photo-stability than the usually used (C6H5C2H4NH3)2PbCl4 (PEPC).

Photostability of 2D Organic-Inorganic Hybrid Perovskites

We analyze the behavior of a series of newly synthesized (R-NH3)2PbX4 perovskites and, in particular, discuss the possible reasons which cause their degradation under UV illumination. Experimental results show that the degradation process depends a lot on their molecular components: not only the inorganic part, but also the chemical structure of the organic moieties play an important role in bleaching and photo-chemical reaction processes which tend to destroy perovskites luminescent framework. In addition, we find the spatial arrangement in crystal also influences the photostability course. Following these trends, we propose a plausible mechanism for the photodegradation of the films, and also introduced options for optimized stability.

Two-Dimensional Perovskite Activation with an Organic Luminophore.

A great advantage of the hybrid organic-inorganic perovskites is the chemical flexibility and the possibility of a molecular engineering of each part of the material (the inorganic part and the organic part respectively) in order to improve or add some functionalities. An adequately chosen organic luminophore has been introduced inside a lead bromide type organic-inorganic perovskite, while respecting the two-dimensional perovskite structure. A substantial increase of the brilliance of the perovskite is obtained. This activation of the perovskite luminescence by the adequate engineering of the organic part is an original approach, and is particularly interesting in the framework of the light-emitting devices such as organic light-emitting diodes (OLEDs) or lasers.

First Occurrence of Tetrazines in Aqueous Solution: Electrochemistry and Fluorescence

The photophysical and electrochemical properties of tetrazines substituted by linear 2,3-naphtalimide antennas and/or adamantane groups specifically dedicated to host-guest interactions with cyclodextrins are studied both in organic and aqueous media. In acetonitrile solvent, the reduction potential of tetrazine leading to the anion radical is shifted, depending on the electron-withdrawing power of the substituent of the tetrazines. Due to the hydrophobic character of these compounds, their solubilization in aqueous solution is achieved successively in presence of either β-cyclodextrins or gold nanoparticules modified by β-cyclodextrins. We demonstrate that the formation of the inclusion compound tetrazine-cyclodextrin allows the solubilization of the tetrazines in aqueous solution. The supramolecular assemblies obtained in water retain tetrazines emission properties, yielding a yellow fluorescence.

New highly electrodeficient cationic fluorescent tetrazines: a step toward the strongest purely organic photooxidants

Strongly fluorescent electrodeficient tetrazines substituted with cationic heterocycles have been prepared. These compounds can be reversibly reduced at a high potential and consequently they are strong oxidants in the excited state. As a result of their very strong photooxidant character, their fluorescence is quenched in the presence of toluene, m-xylene, styrene and sometimes even benzene, through a photoinduced electron transfer reaction via a dynamic quenching mechanism. Beyond their photooxidizing properties, these new molecules have potential towards the realization of new fluorescence sensors. As an example, tetrazine 3 has been dispersed on silica particles and we have demonstrated that its fluorescence is quenched upon exposure to benzene vapors.

CHAPTER 4:Use of Light in Fingerprint Detection

In this chapter, visual examination of fingerprints under various lightings (visible, UV, IR) is discussed. The main methods of fingermark development on porous and non-porous surfaces which use fluorescence to optimize the contrast between the fingerprint and its substrate are described. Lastly, miscellaneous and sometimes prospective methods using light and/or fluorescence to reveal fingerprints are broached.