Luminescent Materials: Metal Complexes, Clusters, and Nanomaterials (2017)

Guest Editors Kenneth Lo and Loïc Charbonnière summarize the development of the field and present an overview of the contributions in this issue. Although the first reports on fluorescence and phosphorescence dated back to the 16th century,1, 2 the term “luminescence”, originating from the Latin “lumen” meaning light, was only introduced in 1888 by the German physicist Eilhardt Wiedemann to encompass all the phenomena where light is produced by means other than heating.1 Probably because it is related to our most important sense, sight, luminescence has fascinated generations of scientists; famous names such as Stokes, Kasha, Jablonsky, Becquerel(s), and many others have made impressive contributions in the field of photon emission. The pioneering works by these scientists are the cornerstones of the understanding of luminescence phenomena and opened the way to technological advances that boosted the field. The 20th century was particularly rich in such breakthroughs, including the development of powerful light sources and lasers,3 monochromators for enhanced spectral resolution,4 and sensitive photomultipliers for optical detection.5 With the availability of commercial spectrophotometers in laboratories in the mid-1950s, it became easier to record and compare luminescence signals and the different pathways for photon generation upon an input of energy. While the earlier works focused essentially on the studies of the two ends of matter in terms of size, namely minerals/bulk solids and small organic/inorganic molecules, recent decades have witnessed the merging of these areas and the development of new luminescent nanomaterials and molecules. Examples include quantum dots (QDs), lanthanide nanoparticles (NPs), metal clusters, and many others, which shine like new stars in the sky of chemists, physicists, and spectroscopists, offering new avenues and applications in chemical, environmental, materials, and biological sciences. With such a long history and diverse areas of research, it is impossible to deliver a survey of luminescent compounds. Instead, our approach was to gather contributions from recognized colleagues in various fields of luminescent materials. We are grateful to all of them and their co-authors for their valuable contributions in this cluster issue and for shedding some new light on these rapidly emerging areas of research. We have the great pleasure to welcome an essay by Jean-Claude Bünzli, who highlights luminescent lanthanide materials, with the state of the art in the field, applications in daily life, and promising perspectives. Two review articles are also included in this cluster issue. The first one by Marco Montalti and co-workers illustrates the latest advances in gold nanoclusters and the approaches used to enhance their luminescence quantum yields. The second one by Jun-Long Zhang and co-authors covers the area of luminescent metallosalens, with an emphasis on their interesting applications in molecular imaging. Solid-state luminescent materials are represented by interesting contributions on very diverse aspects. Victor Castaing, Bruno Viana, and co-authors illustrate the persistent luminescence of Cr-doped glass ceramics, while Ting Wen, Yannan Zhou, Baocheng Yang, and Yonggang Wang describe the structure–activity relationship of luminescent Eu oxyfluorides. The intriguing structural and luminescence properties of AgI polymers are reported by Shun-Ze Zhan, Dan Li, and co-authors, and the thermal and mechanochemical synthesis of luminescent CuI complexes are described by Masako Kato and her group. At the border of the solid-state and solution chemistry of luminescent compounds, we have exciting contributions focusing on luminescent NPs. In an article recommended by the peer review as a Very Important Paper, Luca Prodi and co-workers describe the collective properties of highly doped NPs and their improved resistance to photobleaching. Another contribution by Alberto Credi and co-authors reports the surface modification of QDs with lipoic acid derivatives. Useful surface functionalization of silica-encapsulated QDs is also described by Joris Sprakel and co-authors. A number of contributions are related to the use of nanosized objects in biological analyses; for example, Manuel Ocaña and co-authors present a microemulsion-based synthesis of multicolor-emitting NPs for computed tomography imaging. Peptide-modified upconverting NPs for tumor-cell targeting are described by Kenneth Yin Zhang and co-workers. The use of related NPs for the ratiometric detection of biological analytes is reported by Sam Hay, Peter Harvey, Louise Natrajan and co-workers, while the more fundamental aspects of energy transfer in core–shell NPs are addressed by Fiorenzo Vetrone, Niko Hildebrandt, and co-workers. At the border of NPs and molecular chemistry, Quan-Ming Wang and co-workers report on the synthesis, structural, and spectroscopic characterization of very elegant Au12Ag14 clusters. Moving on to the molecular scale, various facets of the huge family of luminescent compounds, especially those of transition metal elements, are explored in this issue. Triplet–triplet annihilation upconversion of PtII acetylide complexes is illustrated in another Very Important Paper by Fangfang Zhong and Jianzhang Zhao. Additionally, the strategic synthesis and photophysical properties of a library of polynuclear complexes of RhIII, RuII, and IrIII, including an elegant Ir7Ru octanuclear complex, are introduced by Kathryn Knuckey and Gareth Williams. The structure–property relationship of cyclometalated PtII complexes is highlighted by Cristian Strassert, Axel Klein, and co-authors, while the lowest-lying triplet state of an IrIII phthalocyanine is characterized by Kei Murata and Kazuyuki Ishii using absorption, magnetic circular dichroism, and emission spectroscopy. Chao-Ping Hsu, Shih-Sheng Sun and co-authors illustrate the case of trinuclear bridged rhenium complexes, with their synthesis, electrochemical, and photophysical properties. The optical properties of strongly phosphorescent IrIII naphthalenebenzimidazole complexes are described by Felix Castellano and co-workers, while the modulation of the photophysical properties of azathioxanthones by lanthanide ions is reported by Riikka Arppe, Thomas Just Sørensen, and co-workers. The remarkable applications of luminescent coordination complexes in analytical sensing are covered by Jianzhuang Jiang and co-workers on azacrown-containing boron–phenylpyrrin derivatives for Cu2+, by Stefano Stagni, Elizabeth New, Massimiliano Massi, and co-authors on terpyridine-functionalized aryl tetrazoles as ratiometric sensors for Zn2+, by Li-Zhu Wu and co-authors on CuI-bridged alkynyl–PtII complexes for the detection of Sr2+, and by Frankie Leung and Vivian Yam on luminescent dinuclear alkynyl–AuI crown ether complexes for K+ sensing. Additionally, the spectroscopic and luminescence properties of coordination complexes have been exploited for bioanalytical applications. Luminescent ReI naphthalimide complexes for imaging fission yeast cells are described by Simon Pope and co-authors, and the photophysical, cellular uptake, and imaging studies of luminescent RuII fructose complexes are highlighted by Kenneth Kam-Wing Lo and co-workers. Furthermore, the interesting anticancer activity of luminescent IrIII complexes modified by cationic peptides is reported by Shin Aoki and co-workers. The two last contributions in this cluster issue are also related to applications of luminescent compounds. Ana de Bettencourt-Dias and co-authors report on lanthanide-doped polycarbonate-based materials for white light generation, while Anatolie Gavriluta, Thomas Fix, Aline Nonat, and co-authors illustrate the use of nanolayers of luminescent EuIII complexes to improve photocurrent generation in copper indium gallium selenide (CIGS) solar cells. This cluster issue would never exist without the inspiring and remarkable contributions from all the authors. Once again, we gratefully acknowledge them for joining us in this exciting and rewarding adventure. Notably, our sincere gratitude is expressed to the many reviewers for their valuable time and effort. As guest editors, we would like to warmly thank the editorial staff of EurJIC for their highly professional guidance throughout all the different stages of the preparation of this cluster issue. We hope that this brief survey of the different aspects of luminescent compounds will give the readers, especially the younger colleagues and newcomers, a flavor of some of the most recent advances in the field. Concerning the future trends of luminescent materials, it is a challenge to propose topics, as there remains plenty of space to explore. However, as long as human beings have vision, we are confident that luminescence will be at the forefront of interdisciplinary scientific research. We will see, as always! Kenneth Kam-Wing Lo obtained his BSc and PhD degrees at The University of Hong Kong in 1993 and 1997, respectively. He then worked as a Croucher Foundation Postdoctoral Research Fellow at the Inorganic Chemistry Laboratory of the University of Oxford. In 1999, he joined the Department of Biology and Chemistry (currently Department of Chemistry) of City University of Hong Kong as an Assistant Professor and has been a Professor since 2011. He received an APA Prize for Young Scientist from the Asian and Oceanian Photochemistry Association in 2005, a Distinguished Lectureship Award from the Chemical Society of Japan in 2011, and a Croucher Senior Research Fellowship from the Croucher Foundation in 2015. He will be one of the Chairs of the 2018 Metals in Medicine Gordon Research Conference, and the Chair of the 23rd International Symposium on Photochemistry and Photophysics of Coordination Compounds (ISPPCC) at City University of Hong Kong in 2019. He is currently on the Editorial Advisory Board of Inorganic Chemistry and is an Associate Editor of RSC Advances. His research interest is the utilization of luminescent inorganic and organometallic transition metal complexes as biomolecular probes, cellular imaging reagents, and photocytotoxic agents. Loïc Charbonnière got an engineer diploma from the chemistry school of Strasbourg in 1991. After a master in organic and supramolecular chemistry at Strasbourg in 1993, he moved to Geneva and obtained a PhD in Science in 1996. He then got a one-year position as first assistant at the University of Lausanne in 1997 and returned to the University of Strasbourg for a postdoctoral fellowship in 1998. In 1999, he was appointed to a position of assistant researcher at the French national scientific research center (CNRS) in Strasbourg. In 2009 he founded the laboratory of molecular engineering applied to analytical sciences, and in 2011 he became research director at the CNRS. His main scientific interests concern the design of ligands for the complexation of elements of interest for analytical applications and bioimaging, with a particular emphasis on lanthanide coordination chemistry, the spectroscopy of f elements, and the engineering of supramolecular complexes.