Special issue in memory of Prof. King-Chuen Lin

Professor King-Chuen Lin (1953–2022): A visionary chemist, a role model of persistent scientist, and an inspiring mentor, who dedicated his fruitful research career to chemical dynamics, analytical spectroscopy, biophysical instrumentation, and nanomaterials. Professor King-Chuen Lin hailed from Kaohsiung, a bustling port city in southern Taiwan. Upon graduation from the esteemed Provincial Kaohsiung High School, he achieved an impressive ranking in the national university entrance examination to enter National Taiwan University (NTU), the premier institution of higher education in Taiwan. In 1975, he earned a Bachelor of Science degree in Chemistry from NTU. Following his mandatory military service, Prof. Lin set his sights on Michigan State University, where he pursued his doctoral studies. Under the guidance of Professor Stanley Crouch, he completed his Ph.D. in Chemistry (with a focus on Physical and Analytical Chemistry) in 1982. Afterward, he embarked on a post-doctoral training experience at Cornell University. In 1984, Prof. Lin returned to his beloved alma mater in Taiwan and joined the Department of Chemistry at NTU, as a faculty member with a joint appointment in the Institute of Atomic and Molecular Sciences (IAMS), Academia Sinica, the preeminent academic research institution in Taiwan directly responsible to the Presidential Office. He was soon promoted to the position of full professor in 1988. In 2006, he was honored with the esteemed title of Distinguished Professor at NTU. Prof. Lin had a distinguished career spanning almost 30 years at NTU and Academia Sinica, establishing himself as a renowned scholar. He received numerous accolades, including prestigious recognitions such as the Distinguished Research Award and Distinguished Research Fellowship from the National Science Council before 2002. In subsequent years, he was honored with the Academic Award from the Chemical Society Located in Taipei (2009) and the Academic Award from the Ministry of Education (2014), further solidifying his reputation as an esteemed chemistry scholar. In 2018, Professor Lin was the recipient of the R.B. Bernstein Award in Stereodynamics (Switzerland), recognizing his outstanding contributions to the field. The following year, he received the highest academic honor in Taiwan, the National Chair Award, from the Ministry of Education in 2019. These prestigious awards and honors underscore Professor Lin's exceptional standing in academia. Prof. Lin, a visionary and productive chemist, demonstrated a remarkable breadth of research interests spanning multiple fields, including chemical dynamics, analytical spectroscopy, biophysical instrumentation, and nanomaterials. His mentorship extended to numerous young chemists across the globe, including graduate students, post-doctoral fellows, and collaborators. Prof. Lin dedicated tireless efforts to various research projects and provided enthusiastic guidance to approximately 20 doctoral students and over 100 master's students, ensuring their successful completion of their graduate studies. In the early years of his career in NTU, Prof. Lin systematically investigated alkali and alkaline-earth atom molecule reactions. By using the pump-and-probe method, the nascent products (such as KH and MgH) were detected for the first time in a single collision by Prof. Lin under bulk conditions. The state-selective reactions of metal atom and hydrogen (M + H2 → MH + H) were also successfully explained in terms of harpoon mechanism. Total cross sections, radiative lifetimes, and temperature-dependences were measured to prove the depopulation channels and bimodality of the reactions. The collision mechanisms (side-on insertion and collinear abstraction) of atom-molecule reactions were confirmed, and our understanding of these model reactions was completed based on Prof. Lin's experimental results. Electronic transition could be selectively achieved via laser excitation, and a series of heat-pipe experiments were carried out for product characterization by Prof. Lin. A critical analysis indicated that the electronic symmetry of the metal-molecule system plays a major role in the reaction instead of the electronic potential barrier, although the height of the potential energy above threshold is also one of the key factors for metal atom molecule reactions. Utilizing the time-resolved pump-and-probe technique, transition state dynamics of the metal-molecule reactions was also investigated in great detail by Prof. Lin during the period. During the 1990s, while maintaining his early focus on studying the reactions of hydrogen with alkali metals or alkali earth metals through LIF spectroscopy and theoretical calculations, Prof. Lin also achieved highly productive research outcomes in gas-phase reaction dynamics. Specifically, he successfully employed laser spectroscopy to elucidate the reaction mechanisms of fundamental reaction steps in atmospheric chemistry. Later, Prof. Lin applied cavity-ring down spectroscopy and velocity map ion imaging method to investigate the halogen-related photo dissociation in atmosphere, such as characterization of atomic halogen, molecular halogen, and hydrogen halide products from photo-dissociation of aliphatic halides. He also utilized step-scan Fourier transform spectroscopy to investigate the rotational and vibrational energy transfer of key radicals in atmosphere, such as CH and SH, in collisions with various gaseous species. In particular, Prof. Lin employed both velocity map ion imaging method and step-scan Fourier transform spectroscopy, as well as theoretical model, to explore the roaming mechanism in photo-dissociation, which is one of hot topics in the field of reaction dynamics during recent decades. Besides the gas-phase studies mentioned above, Prof. Lin also utilized several spectroscopic methods, such as evanescent-wave cavity-ring down spectroscopy, step-scan Fourier transform spectroscopy, and single-molecule spectroscopy, to investigate interface chemistry, such as elucidating the dynamics of catalytic isomerization of quadricyclane, probing molecular adsorptions at silica interfaces and electron transfer on nanoparticles. During the last decade of his career, Prof. Lin was dedicated to the pursuit of the holy grail in stereodynamics, which involves sorting molecules in order and thus controlling its chemistry. Together with Prof. Toshio Kasai, he built a “chemical microscope” which couples the techniques of high-voltage hexapole guide as a quantum-state selector, brute-force orientation method for making state-selected molecules “to stand still,” and velocity map ion imaging for “taking a photo” of product species created from spatially oriented molecules subjected to reaction. This state-of-the-art apparatus has been employed to image the stereodynamics of halogen-related photo-dissociation, such as uncovering the vector correlation within the reaction mechanism; furthermore, it promises to distinguish the enantiomers of chiral molecules. Prof. Lin's outstanding contributions have been recognized through various awards. In 2018, he was honored with the R.B. Bernstein Award in Stereodynamics, which is one of prestigious international awards for chemistry. The following year, in 2019, he received the National Chair Award of Ministry of Education, which is the most prestigious award in Taiwan for full-time professors actively engaged in academic research and teaching. Prof. Lin's research encompassed not only gas-phase chemical kinetics but also applied laser spectroscopy and analytical chemistry, specifically emphasizing ultra-trace elemental analysis. Upon returning to Taiwan in 1984, Prof. Lin resumed his research in analytical chemistry, focusing on laser-enhanced ionization (LEI) techniques, which were essential in his dissertation research. In 3 years, he successfully developed a unique dual-laser enhancement method by utilizing a nitrogen laser as the second excitation source. An achievement was made by utilizing a second harmonic YAG laser source for resonance excitation followed by a nitrogen laser source for two-photon excitation, resulting in a distinctive combination. This achievement improved the detection limit by more than two orders of magnitude. The details of the theoretical model of this dual-laser method were thoroughly investigated through international collaborations. Furthermore, Prof. Lin utilized LEI techniques to develop novel methods for temperature and analyte ionization efficiency determination. With advanced LEI techniques reaching unprecedented maturity, Prof. Lin began developing various novel instruments with LEI detection by combining flow injection, ion exchange chromatography, and gas chromatography as sample inlet and pretreatment tools to explore more analytical applications for real sample determinations. Simultaneously, he continued to work tirelessly on new aspects of using LEI techniques, such as spatially resolved flame temperature mappings and the ionization efficiency of alkali halides, which are the main interference species in flames. Later, two branches of research activities in trace elemental analysis, inductively coupled plasma mass spectrometry (ICP-MS) and laser-induced breakdown spectroscopy (LIBS), were established in Prof. Lin's laboratory. Around 1995–2000, Prof. Lin launched several research projects focusing on trace elemental analysis in seawater and organic solutions using ICP-MS. The main focus was to develop smart sample introduction systems to reduce the background due to the matrix effect and thereby improve the sensitivity and applicability of ICP/MS. For example, a smart sample introduction system combining a flow-injection system and a home-built ultrasonic nebulizer-membrane dryer was developed to remove the organic matrix, which causes serious problems and extinguishes the argon plasma. Prof. Lin's research in this direction enabled the direct detection of trace lead concentration in aqueous solutions and seawater containing organic species using ICP/MS. Starting in the year 2000, Prof. Lin started a new research direction based on atomic spectroscopy-based elemental analysis using LIBS, an atomic emission technique based on laser ablation. Although the detection limit is not as good as ICP/MS, it still attracted much attention because it is a simple and rapid method that allows remote elemental analysis in hostile environments. One major drawback of LIBS is the serious shot-to-shot signal fluctuation, which makes the application of LIBS to liquid samples a big challenge. At that time, most of the studies focused on spinning solid samples and only a few works were about liquid samples. Prof. Lin led the research team and developed a new type of liquid sample introduction system for LIBS to minimize the serious shot-to-shot signal fluctuation in liquid LIBS. In this scheme, the aqueous sample was introduced to the laser pulses by a homemade electrospray device. The laser pulses were focused onto the tip of the Taylor cone of the electrospray, and the emission signal and the ion currents from the laser-induced breakdown of the liquid sample are collected concurrently to remove the shot-to-shot signal fluctuation. This novel method greatly improved the sensitivity of LIBS for liquid samples. Later, optical multi-channel analyzer was also introduced to study the plasma temperature which was also used as a reference signal to remove the fluctuation. Several follow-ups were published in this direction to demonstrate the power of this developed method. Prof. Lin, a world-class chemical instrumentationist, commenced utilizing his exceptional spectroscopic expertise to pioneer the development of innovative biophysical equipment around the turn of the millennium. An evanescent wave cavity ring-down absorption spectroscopy (EW-CRDS) was developed in the laboratory around 2002 to measure the thermodynamic properties of surface adsorption. The combination of evanescent wave cavity ring-down and dichroism absorption techniques proves to be an effective approach for investigating the orientation of adsorbed molecules at the interface. Subsequently, this technique was adapted to study the interaction between deoxyribonucleic acids (DNA) and functionalized gold nanoparticles (AuNPs). By employing surface-functionalized gold nanoparticles (AuNPs), EW-CRDS has been successfully utilized as a sensing tool for the quantitative detection of Matrix metallopeptide 9 (MMP-9), a biomarker for tumor migration, as well as prostate-specific antigen, a biomarker for prostate cancer, within the laboratory setting. Around the millennium year, single-molecule microscopy had become an emerging biophysics field. Prof. Lin noticed this trend and was highly interested in this topic. To introduce the new research direction, he first initiated a weekly reading club with several Ph.D. students to read the famous book “Single-Molecule Optical Detection, Imaging, and Spectroscopy” edited by Basché, Moerner, Orrit, and Wild. Later in 2003, Prof. Lin sent a Ph.D. student to Prof. Edward Yeung's group at Lowa State University to learn single-molecule microscopy. In 2005, Prof. Lin obtained the fund and was able to purchase the first confocal fluorescence microscope for single-molecule imaging for the group. After a few years and several generations of students, the first scientific paper focusing on the photoinduced electron transfer between Oxazine-1 dye molecules and TiO2 nanoparticles at a single-molecule level from this microscope was published. Furthermore, this technique has been applied to investigate lipid dynamics in the lipid bilayer of small unilamellar vesicles and to probe oxygen gradient across micro-fluidic channels. Until 2022, single-molecule microscopy and spectroscopy remained an important research direction in Prof. Lin's group. The development of the research direction of single-molecule microscopy is a clear example of Prof. Lin's sharp scientific sense as well as his great patience and persistence in conducting research. Prof. Lin did indeed demonstrate his skill over the span of last 10 years and assisted in establishing and implementing his research focus on the synthesis and applications of carbon and silicon quantum dots for selective detection of metal ions in his laboratory. Later on, he focused on synthesis, characterization, photophysical properties, and applications of metal nanoparticle-based functional nanomaterials. Prof. Lin was a sincere and intelligent scientist who was enthusiastic and highly motivated, particularly impressive was his ability to learn new nano-related techniques quickly, and, perhaps more importantly, capable of carrying out research independently. Besides having a strong interest in nanoscience, he also had a solid understanding of recent advancements in the field nanochemistry, particularly in the areas material chemistry, synthesis of ultrafine nanomaterials and using various characterization techniques, electrochemistry, and biosensors. Undoubtedly, he was skilled in their application over a wide span of interesting areas, such as nanocatalysis, biosensing of drugs, catalysis, and energy storage systems. Moreover, he was also a modest gentleman who was diligent and had a high value for teamwork. He has done excellent work on several research topics including synthesis, characterization of carbon porous materials (CPMs) from biomass and applications for catalytic and energy-related areas, semiconductor and metal doped carbon dots nanomaterials for photocatalytic degradation of toxic pesticides, herbicides, and chromium. Several joint projects were carried out successfully and resulted in publication of about four dozen high-quality SCI journals including 8 review articles and 6 book chapters. Unfortunately, Prof. Lin passed away in June 2022. It is difficult to describe, in just a few sentences, the extraordinary human and scientific personality of Lin. He was an unattainable model to imitate, a mentor, and a teacher not only for us, but also for many other his former students and associates and even collaboration colleagues from outside NTU. He left an indelible mark on the professional and personal lives of all of us and his absence arouses a deep sense of emptiness. We attempt to describe the scientific character of Lin and what he symbolizes to those who knew him and held him in high esteem. This special issue is a collection of papers that showcase the diverse research interests of Prof. Lin in the fields of physical chemistry, analytical chemistry, biophysics, and material chemistry. These papers have been contributed by Prof. Lin's friends, colleagues, and former group members. The global chemistry community deeply mourns the loss of Prof. Lin, and through this special issue, the invited contributors aim to honor his memory. We extend our heartfelt gratitude to the Journal of the Chinese Chemical Society (JCCS) for publishing this commemorative issue, which serves as a testament to Prof. Lin's significant scientific contributions.