Coauthored Publications with: Lin

Journal Article

Nakamura, M, Tsai P-Y, Kasai T, Lin K-C, Palazzetti F, Lombardi A, Aquilanti V.  2015.  Dynamical, spectroscopic and computational imaging of bond breaking in photodissociation: Roaming and role of conical intersections. Faraday Discussions. 177:77-98. AbstractWebsite

Recent experimental and theoretical advances in the study of the dissociation of excited molecules are revealing unexpected mechanisms, when their outcomes are tackled by combining (i) space-time ion imaging of translational features, with (ii) spectroscopic probing of rotational and vibrational distributions; crucial is the assistance of (iii) the quantum chemistry of structural investigations of rearrangements of chemical bonds, and of (iv) the simulations of molecular dynamics to follow the evolution of selective bond stretching and breaking. Here we present results of such an integrated approach to methyl formate, HCOOCH3, the simplest of esters; the main focus is on the rotovibrationally excited CO (v = 1) product and in general on the energy distribution in the fragments. Previous laser studies of dissociation into CO and CH3OH at a sequence of various wavelengths discovered signatures of a roaming mechanism by the late arrival of CO (v = 0) products in time-of-flight ion imaging. Subsequent detailed investigations as a function of excitation energy provided the assessment of the threshold, which opens for triple breakdown into CO and further fragments H and CH3O, as spectroscopically characterized by ion imaging and FTIR respectively. Accompanying quantum mechanical electronic structure calculations and classical molecular dynamics simulations clarify the origin of these fragments through "roaming" pathways involving incipient radical intermediates at energies below the triple fragmentation threshold: a specific role is played by nonadiabatic transitions at a conical intersection between ground and excited states; alternative pathways focalize our attention to regions of the potential energy surfaces other than those in the neighbourhoods of saddle points along minimum energy paths: eventually this leads us to look for avenues in reaction kinetics beyond those of venerable transition state theories. This journal is © The Royal Society of Chemistry.
Li, H-K, Tsai P-Y, Hung K-C, Kasai T, Lin K-C.  2015.  Communication: Photodissociation of CH3CHO at 308 nm: Observation of H-roaming, CH3-roaming, and transition state pathways together along the ground state surface. Journal of Chemical Physics. 142, Number 4 AbstractWebsite

Following photodissociation of acetaldehyde (CH3CHO) at 308 nm, the CO(v = 1-4) fragment is acquired using time-resolved Fourier-transform infrared emission spectroscopy. The CO(v = 1) rotational distribution shows a bimodal feature; the low- and high-J components result from H-roaming around CH3CO core and CH3-roaming around CHO radical, respectively, in consistency with a recent assignment by Kable and co-workers (Lee et al., Chem. Sci. 5, 4633 (2014)). The H-roaming pathway disappears at the CO(v 2) states, because of insufficient available energy following bond-breaking of H + CH3CO. By analyzing the CH4 emission spectrum, we obtained a bimodal vibrational distribution; the low-energy component is ascribed to the transition state (TS) pathway, consistent with prediction by quasiclassical trajectory calculations, while the high-energy component results from H- and CH3-roamings. A branching fraction of H-roaming/CH3-roaming/TS contribution is evaluated to be (8% ± 3%)/(68% ± 10%)/(25% ± 5%), in which the TS pathway was observed for the first time. The three pathways proceed concomitantly along the electronic ground state surface. © 2015 AIP Publishing LLC.
Chang, C-L, Tsai P-Y, Chang Y-P, Lin K-C.  2012.  Interfacial electron transfer from CdSe/ZnS quantum dots to TiO 2 nanoparticles: Size dependence at the single-molecule level. ChemPhysChem. 13:2711-2720., Number 11 AbstractWebsite

Electron transfer (ET) kinetics of CdSe/ZnS core/shell quantum dots (QDs) on bare coverslips and a TiO 2 nanoparticle-coated thin film has been investigated at the single-molecule level. The QDs prepared have three different diameters of 3.6, 4.6, and 6.4 nm. The trajectories of fluorescence intensity are acquired with respect to the arrival time. The on-time events and subsequent fluorescence lifetimes are shorter with decreasing size. Given the lifetime measurements for QDs on glass and TiO 2, the rate constant of ET from QDs to TiO 2 may be determined to be 1.3×10 7, 6.0×10 6, and 4.7×10 6 s -1 for the increasing sizes of the QDs. The plot of on-time probability density versus arrival time is characterized by power-law statistics in the short time region and a bending tail in the long time region. Marcus's ET model is employed to satisfactorily fit the bending tail behavior and to further calculate the ET rate constants. The theoretical counterparts for the different sizes are 1.4×10 7, 6.4×10 6, and 1.9×10 6 s -1, showing good agreement with the experimental results. Going dotty: Electron transfer kinetics of CdSe/ZnS core/shell quantum dots (QDs) on bare coverslips and on TiO 2 nanoparticle coated thin films have been investigated at the single-molecule level. As the size of the QDs changes, the shift in the valence band (VB) energy is less significant than the shift in the conduction band (CB) energy. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Tsai, P-Y, Che D-C, Nakamura M, Lin K-C, Kasai T.  2010.  Orientation dependence in the four-atom reaction of OH + HBr using the single-state oriented OH radical beam. Physical Chemistry Chemical Physics. 12:2532-2534., Number 11 AbstractWebsite

The orientation dependence for the Br atom formation in the reaction of the oriented OH radicals with HBr molecules at 0.26 eV collision energy has been observed for the first time using the hexapole electric field, and we found that the reaction cross-section for O-end attack is more favorable than that for H-end attack by a factor of 3.4 ± 2.3. © the Owner Societies.
Lin, K-C, Tsai P-Y, Chao M-H, Nakamura M, Kasai T, Lombardi A, Palazzetti F, Aquilanti V.  2018.  Roaming signature in photodissociation of carbonyl compounds. International Reviews in Physical Chemistry. 37:217-258., Number 2 AbstractWebsite

An alternative to the transition state (TS) pathway, the roaming route, which bypasses the minimum energy path but produces the same molecular products, was recently found in photodissociation dynamics. This account describes signatures of roaming in photodissociation of the carbonyl compounds, specifically methyl formate and aliphatic aldehydes. Methyl formate was promoted to the excited state, followed by internal conversion via a conical intersection. Then, the energetic precursor dissociated to fragments which proceeded along either TS or roaming path. In contrast to the lack of a roaming saddle point found in methyl formate, the structure of the roaming saddle point for each of a series of aliphatic aldehydes comprises two moieties that are weakly bound at a distance. As its size increases, the energy difference between the TS barrier and the roaming saddle point increases and the roaming pathway becomes increasingly dominant. Experimentally, the rotational-level dependence of the roaming route was measured with ion imaging, while the vibrational-state dependence was observed with time-resolved Fourier-transform infrared emission spectroscopy. The roaming signature was verified theoretically by quasi-classical trajectory (QCT) calculations. As an alternative to the QCT method, a multi-center impulsive model was developed to simulate the roaming scalar and vector properties. © 2018 Informa UK Limited, trading as Taylor & Francis Group.
Tsai, P-Y, Hung K-C, Li H-K, Lin K-C.  2014.  Photodissociation of propionaldehyde at 248 nm: Roaming pathway as an increasingly important role in large aliphatic aldehydes. Journal of Physical Chemistry Letters. 5:190-195., Number 1 AbstractWebsite

Time-resolved Fourier transform infrared emission spectroscopy is employed in the photolysis of propionaldehyde (CH3CH2CHO) at 248 nm to characterize the role of the roaming pathway. High-resolution spectra of CO are analyzed to yield a single Boltzmann rotational distribution for each vibrational level (ν = 1-4) with small rotational and large vibrational energy disposals. A roaming saddle point is found containing two far separated moieties of HCO and CH3CH2 with a weak interaction between them. Quasiclassical trajectory calculations on this configuration yield the CO energy flow behavior, consistent with the findings. The rate constant along the roaming pathway is evaluated to be larger by >1-2 orders of magnitude than those along tight transition state or three-body dissociation pathways. This work implies that the roaming mechanism plays an increasingly important role in aliphatic aldehydes as the molecular size becomes larger. © 2013 American Chemical Society.
Wu, C-C, Lin H-C, Chang Y-B, Tsai P-Y, Yeh Y-Y, Fan H, Lin K-C, Francisco JS.  2011.  Br 2 molecular elimination in photolysis of (COBr) 2 at 248 nm by using cavity ring-down absorption spectroscopy: A photodissociation channel being ignored. Journal of Chemical Physics. 135, Number 23 AbstractWebsite

A primary dissociation channel of Br 2 elimination is detected following a single-photon absorption of (COBr) 2 at 248 nm by using cavity ring-down absorption spectroscopy. The technique contains two laser beams propagating in a perpendicular configuration. The tunable laser beam along the axis of the ring-down cell probes the Br 2 fragment in the B 3Π + ou-X 1Σ g + transition. The measurements of laser energy- and pressure-dependence and addition of a Br scavenger are further carried out to rule out the probability of Br 2 contribution from a secondary reaction. By means of spectral simulation, the ratio of nascent vibrational population for v = 0, 1, and 2 levels is evaluated to be 1:(0.65 ± 0.09):(0.34 ± 0.07), corresponding to a Boltzmann vibrational temperature of 893 ± 31 K. The quantum yield of the ground state Br 2 elimination reaction is determined to be 0.11 ± 0.06. With the aid of ab initio potential energy calculations, the pathway of molecular elimination is proposed on the energetic ground state (COBr) 2 via internal conversion. A four-center dissociation mechanism is followed synchronously or sequentially yielding three fragments of Br 2 + 2CO. The resulting Br 2 is anticipated to be vibrationally hot. The measurement of a positive temperature effect supports the proposed mechanism. © 2011 American Institute of Physics.
Nakamura, M, Palazzetti F, Tsai P-Y, Lin K-C, Kasai T, Che D-C, Lombardi A, Aquilanti V.  2019.  Vectorial imaging of the photodissociation of 2-bromobutane oriented: Via hexapolar state selection. Physical Chemistry Chemical Physics. 21(26):14164-14172. AbstractWebsite

Molecular orientation techniques are becoming available in the study of elementary chemical processes, in order to highlight those structural and dynamical properties that would be concealed by random rotational motions. Recently successful orientation was achieved for asymmetric-top and chiral molecules of much larger complexity than hitherto. In this work, we report and discuss the correlation between the vectors' photofragment recoil velocity v, transition dipole moment μ, and permanent dipole moment d in a dissociation experiment on hexapole oriented 2-bromobutane, photoinitiated by a linearly polarized laser. The sliced ion images of the Br∗(2P1/2) and Br(2P3/2) photofragments were acquired at 234.0 and 254.1 nm, respectively, by a (2 + 1) resonance-enhanced multiphoton ionization technique. A detailed analysis of the sliced ion images obtained at a tilting angle 45° of laser polarization provides information on the correlation of the three vectors, which are confined by two polar angles α and χ and one azimuthal angle φμd in the recoil frame. The sliced ion images of Br fragments eliminated individually from the enantiomers at 254.1 nm yield an asymmetric factor close to zero; for this reason the photofragment angular distributions do not show significant differences. The elimination of the Br∗ fragment at 234.0 nm is mainly correlated with a parallel transition, giving rise to a large anisotropy parameter of 1.85, and thus can be considered as a single state excitation. The resulting recoil frame angles are optimized to 163° ± 8° and 164° ± 1° for α and χ, respectively, whereas φμd is approaching 0° for the best fit. Since for the present molecule, the three vectors have an only slight spatial arrangement, the photofragment angular distributions of the two enantiomers do not show appreciable differences. Theoretical and computational simulations provide us the basis to state that oriented enantiomers can be discriminated on-the-fly in photodissociation processes even initiated by non-circularly polarized light, provided that the three vectors encountered above have specific three-dimensional arrangements. The fact that Br fragment elimination involves a multi-potential dissociation carries uncertainties in theoretical estimates of the vector direction. Therefore, this work represents a preliminary but significant step on the road to chiral discrimination on-the-fly, which is shown to be best propitiated in molecules where vectors are far from having degenerate mutual angular directions. © 2019 the Owner Societies.
Lin, C.-H., WCLLKCSMSML-XK-.  2020.  Non-invasive and time-dependent blood-sugar monitoring via breath-derived CO2 correlation using gas chromatograph with a milli-whistle gas analyze. AbstractWebsite

A clear and positive correlation between the CO2 concentration and the blood-sugar level has been observed via a noninvasive and time-dependent monitoring of CO2 concentration from human breath, which is carried out by using a homemade gas chromatography (GC)/milli-whistle compact analyzer. The time-dependent sampling of the CO2 concentration correlated between 5.0 to 5.6% (1% = 104 ppm) in accordance with blood-sugar level variations of 80 to 110 mg/dL. The analytical method results in a rapid, continuous and non-invasive determination of blood-sugar level via measurement of the CO2 concentration exhaled from the lungs.
Dhenadhayalan, N, Lin K-C, Suresh R, Ramamurthy P.  2016.  Unravelling the Multiple Emissive States in Citric-Acid-Derived Carbon Dots. Journal of Physical Chemistry C. 120:1252-1261., Number 2 AbstractWebsite

Steady-state and time-resolved fluorescence spectroscopy techniques were used to probe multifluorescence resulting from citric-acid-derived carbon dots (C-dots). Commonly, both carboxyl-/amine-functionalized C-dots exhibit three distinct emissive states corresponding to the carbon-core and surface domain. The shorter-wavelength fluorescence (below 400 nm) originates from the carbon-core absorption band at ∼290 nm, whereas the fluorescence (above 400 nm) is caused by two surface states at ∼350 and 385 nm. In addition to three emissive states, a molecular state was also found in amine-functionalized C-dots. Time-resolved emission spectra (TRES) and time-resolved area normalized emission spectra (TRANES) were analyzed to confirm the origin of excitation wavelength-dependent fluorescence of C-dots. The surface functional groups on the C-dots are capable of regulating the electron transfer to affect the multifluorescence behavior. The electron transfer takes place from the carbon-core to surface domain by the presence of -COOH on the surface and vice versa for the case of -NH2 present on the surface. To the best of our knowledge, this is the first report that the multiemissive states are probed in C-dots systems using TRES and TRANES analyses, and related fluorescence mechanisms are verified clearly. © 2015 American Chemical Society.
Chao, M-S, Tornero J, Lin KC, Stolte S, González Ureña A.  2013.  Decoherence cross-section in NO + Ar collisions: Experimental results and a simple model. Journal of Physical Chemistry A. 117:8119-8125., Number 34 AbstractWebsite

Quantum decoherence can be viewed as the mechanism responsible for the quantum-to-classical transition as the initially prepared quantum state interacts with its environment in an irreversible manner. One of the most common mechanisms responsible for the macroscopically observed decoherence involves collisions of an atom or molecule, initially prepared in a coherent superposition of states, with gas particles. In this work, a coherent superposition of quantum internal states of NO molecules is prepared by the interaction between the molecule with both a static and a radiofrequency electric field. Subsequently, NO + Ar collision decoherence experiments are investigated by measuring the loss of coherence as a function of the number of collisions. Data analysis using a model based on the interaction potential of the collisional partners allowed to unravel the molecular mechanism responsible for the loss of coherence in the prepared NO quantum superposition of internal states. The relevance of the present work relies on several aspects. On the one hand, the use of radio-waves introduces a new way for the production of coherent beams. On the other hand, the employed methodology could be useful in investigating the Stereodynamics of chemical reactions with coherent reagents. © 2013 American Chemical Society.
Chen, S-Y, Tsai P-Y, Lin H-C, Wu C-C, Lin K-C, Sun BJ, Chang AHH.  2011.  I2 molecular elimination in single-photon dissociation of CH2I2 at 248 nm by using cavity ring-down absorption spectroscopy. Journal of Chemical Physics. 134, Number 3 AbstractWebsite

Following single-photon dissociation of CH2I2 at 248 nm, I2 molecular elimination is detected by using cavity ring-down absorption spectroscopy. The technique comprises two laser beams propagating in a perpendicular configuration, in which a tunable laser beam along the axis of the ring-down cell probes the I2 fragment in the B 3 ou + - X 1 g + transition. The nascent vibrational populations for v 0, 1, and 2 levels are obtained with a population ratio of 1:(0.65 0.10):(0.30 0.05), corresponding to a Boltzmann-like vibrational temperature of 544 73 K. The quantum yield of the ground state I2 elimination reaction is determined to be 0.0040 0.0025. With the aid of ab initio potential energy calculations, the pathway of molecular elimination is proposed on the energetic ground state CH2I2 via internal conversion, followed by asynchronous three-center dissociation. A positive temperature effect supports the proposed mechanism. © 2011 American Institute of Physics.
Srinivasan, V, Jhonsi MA, Lin K-C, Ananth DA, Sivasudha T, Narayanaswamy R, Kathiravan A.  2019.  Pyrene-based prospective biomaterial: In vitro bioimaging, protein binding studies and detection of bilirubin and Fe3+. Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy. 211 AbstractWebsite

Herein, we have meticulously derived the nanosized fluorescent aggregates from pyrene Schiff base (PS) in DMSO:water (10:90) ratio. The aggregation property of PS molecule was characterized by SEM and TEM measurements, revealed the aggregated particles are in spherical shape with ~3 nm in size. Moreover, aggregates exhibit a high fluorescence quantum yield (48%) which was effectively used for the in vitro bioimaging of two different cancer cells such as A549 and MCF-7 cells in which it exhibiting excellent biocompatibility. Further, it was estimated the capability of twofold acridine orange/ethidium bromide (AO/EB) staining to identify the apoptotic associated changes in cancer cells. Additionally, the aggregates were successfully demonstrated as a luminescent probe for the perceptive biomolecule detection of bilirubin. On the other hand, the PS molecule was successfully utilized for protein binding and metal ion sensing studies. The interaction of bovine serum albumin (BSA) with PS molecule in DMSO was using fluorescence spectroscopic method and nature of interaction was also confirmed through molecular docking analysis. The PS molecule also acts as an excellent sensor for biologically important Fe3+ ion with detection limit of 336 nM. Overall, PS molecule can be a prospective material in biological field both in solution as well as aggregated forms. © 2019 Elsevier B.V.
Veerakumar, P, Thanasekaran P, Lin K-C, Liu S-B.  2017.  Biomass Derived Sheet-like Carbon/Palladium Nanocomposite: An Excellent Opportunity for Reduction of Toxic Hexavalent Chromium. ACS Sustainable Chemistry and Engineering. 5:5302-5312., Number 6 AbstractWebsite

Palladium nanoparticles (Pd NPs) immobilized on a garlic skin-derived activated carbons (GACs) is reported. The morphology, structure, surface compositions, and textural properties of the GACs and Pd@GAC catalyst were investigated by a variety of physicochemical characterization techniques, which revealed a dispersion of Pd NPs with average particle size of ca. 21 nm on sheet-like graphitized GACs with surface areas and pore volumes as high as 1836 m2 g-1 and 0.89 cm3 g-1, respectively. As a result, the Pd@GAC with a Pd loading of ca. 1-2 wt% exhibited superior activity for catalytic reduction of toxic Cr(VI) to Cr(III) surpassing most metal-based catalysts reported in the literature. As evidenced by a comprehensive UV-vis spectrophotometric study, the eco-friendly Pd@GAC catalyst reported herein, which can be facilely prepared with biowaste feedstocks, also showed excellent catalytic performances for efficient reduction of Cr(VI) with extraordinary stability and recyclability over at least five repeated catalytic test cycles. © 2017 American Chemical Society.
Dhenadhayalan, N, Lin K-C.  2015.  Chemically Induced Fluorescence Switching of Carbon-Dots and Its Multiple Logic Gate Implementation. Scientific Reports. 5 AbstractWebsite

Investigations were carried out on the carbon-dots (C-dots) based fluorescent off - on (Fe 3 €‰+ €‰ - S 2 O 3 2 ') and on - off (Zn 2 €‰+ €‰ - PO 4 3 ') sensors for the detection of metal ions and anions. The sensor system exhibits excellent selectivity and sensitivity towards the detection of biologically important Fe 3 €‰+ €‰, Zn 2 €‰+ €‰ metal ions and S 2 O 3 2 ', PO 4 3 ' anions. It was found that the functional group on the C-dots surface plays crucial role in metal ions and anions detection. Inspired by the sensing results, we demonstrate C-dots based molecular logic gates operation using metal ions and anions as the chemical input. Herein, YES, NOT, OR, XOR and IMPLICATION (IMP) logic gates were constructed based on the selection of metal ions and anions as inputs. This carbon-dots sensor can be utilized as various logic gates at the molecular level and it will show better applicability for the next generation of molecular logic gates. Their promising properties of C-dots may open up a new paradigm for establishing the chemical logic gates via fluorescent chemosensors.
Veerakumar, P, Dhenadhayalan N, Lin K-C, Liu S-B.  2015.  Highly stable ruthenium nanoparticles on 3D mesoporous carbon: An excellent opportunity for reduction reactions. Journal of Materials Chemistry A. 3:23448-23457., Number 46 AbstractWebsite

Carbon mesoporous materials (CPMs) have great potential in the field of heterogeneous catalysis. Highly dispersed ruthenium nanoparticles (RuNPs) embedded in three dimensional (3D) CPMs as catalysts with a high surface area (1474 m2 g-1) were prepared by microwave-thermal reduction processes. Characterization technologies including X-ray diffraction (XRD), N2 adsorption/desorption isotherm measurements, field emission transmission electron microscopy (FE-TEM), thermogravimetric analysis (TGA), hydrogen temperature-programmed reduction (H2-TPR), Raman spectroscopy and 13C solid state cross polarization and magic angle spinning (13C CP/MAS) NMR spectroscopy were utilized to scrutinize the catalysts. It was revealed that the Ru/CPM catalysts exhibited a highly ordered 3D mesoporous structure and a large surface area and were widely used as catalysts for reduction reactions. Reduction of p-nitroaniline (p-NA) and crystal violet (CV) using NaBH4 with the use of this catalyst was studied by means of UV-vis spectroscopy. Here, NaBH4 acts as a hydrogen donor. This catalyst shows an excellent catalytic activity towards reduction of p-NA and CV dye at room temperature. Due to the promising properties of CPMs, they can be utilized to fabricate 3D carbon-based materials for a variety of novel applications. © The Royal Society of Chemistry 2015.
Fan, H, Tsai P-Y, Lin K-C, Lin C-W, Yan C-Y, Yang S-W, Chang AHH.  2012.  Molecular elimination of Br2 in photodissociation of CH 2BrC(O)Br at 248 nm using cavity ring-down absorption spectroscopy. Journal of Chemical Physics. 137, Number 21 AbstractWebsite

The primary elimination channel of bromine molecule in one-photon dissociation of CH2BrC(O)Br at 248 nm is investigated using cavity ring-down absorption spectroscopy. By means of spectral simulation, the ratio of nascent vibrational population in v 0, 1, and 2 levels is evaluated to be 1:(0.5 ± 0.1):(0.2 ± 0.1), corresponding to a Boltzmann vibrational temperature of 581 ± 45 K. The quantum yield of the ground state Br2 elimination reaction is determined to be 0.24 ± 0.08. With the aid of ab initio potential energy calculations, the obtained Br2 fragments are anticipated to dissociate on the electronic ground state, yielding vibrationally hot Br2 products. The temperature-dependence measurements support the proposed pathway via internal conversion. For comparison, the Br2 yields are obtained analogously from CH3CHBrC(O)Br and (CH3)2CBrC(O)Br to be 0.03 and 0.06, respectively. The trend of Br2 yields among the three compounds is consistent with the branching ratio evaluation by Rice-Ramsperger-Kassel-Marcus method. However, the latter result for each molecule is smaller by an order of magnitude than the yield findings. A non-statistical pathway so-called roaming process might be an alternative to the Br2 production, and its contribution might account for the underestimate of the branching ratio calculations. © 2012 American Institute of Physics.
Chen, Y-J, Tzeng H-Y, Fan H-F, Chen M-S, Huang J-S, Lin K-C.  2010.  Photoinduced electron transfer of oxazine 1/TiO2 nanoparticles at single molecule level by using confocal fluorescence microscopy. Langmuir. 26:9050-9060., Number 11 AbstractWebsite

Kinetics of photoinduced electron transfer (ET) from oxazine 1 dye to TiO2 nanoparticles (NPs) surface is studied at a single molecule level by using confocal fluorescence microscopy. Upon irradiation with a pulsed laser at 630 nm, the fluorescence lifetimes sampled among 100 different dye molecules are determined to yield an average lifetime of 2.9 ± 0.3 ns, which is close to the value of 3.0 ± 0.6 ns measured on the bare coverslip. The lifetime proximity suggests that most interfacial electron transfer (IFET) processes for the current system are inefficient, probably caused by physisorption between dye and the TiO2 film. However, there might exist some molecules which are quenched before fluorescing and fail to be detected. With the aid of autocorrelation analysis under a three-level energy system, the IFET kinetics of single dye molecules in the conduction band of TiO2 NPs is evaluated to be (1.0 ± 0.1)×104 s-1 averaged over 100 single molecules and the back ET rate constant is 4.7 ± 0.9 s-1. When a thicker TiO2 film is substituted, the resultant kinetic data do not make a significant difference. The trend of IFET efficacy agrees with the method of fluorescence lifetime measurements. The obtained forward ET rate constants are about ten times smaller than the photovoltage response measured in an assembled dye-sensitized solar cell. The discrepancy is discussed. The inhomogeneous and fluctuation characters for the IFET process are attributed to microenvironment variation for each single molecule. The obtained ET rates are much slower than the fluorescence relaxation. Such a small ET quantum yield is yet feasibly detectable at a single molecule level. © 2010 American Chemical Society.
Veerakumar, P, Rajkumar C, Chen S-M, Thirumalraj B, Lin K-C.  2018.  Activated porous carbon supported rhenium composites as electrode materials for electrocatalytic and supercapacitor applications. Electrochimica Acta. 271:433-447. AbstractWebsite

In this study, we developed highly dispersed rhenium nanoparticles decorated on activated carbon (Re@CDACs). The activated carbons were derived from the biomass raw materials cardamom pods (Elettaria cardamomum L) via carbonization followed by activation with ZnCl2 at high temperature. The Re NPs synthesis was achieved by decomposition of [Re2(CO)10] complex via a facile microwave thermal reduction technique. The as-prepared Re@CDACs nanocomposites were characterized by a combination of state-of-the-art techniques. The Re@CDACs nanocomposites so prepared were utilized for electrocatalytic oxidation of sunset yellow (SY) and supercapacitor applications. The Re@CDACs-modified electrodes were found to show extraordinary electrochemical performance for sensitive and selective detection of SY with a wide linear range of 0.05–390 μM and a detection limit and sensitivity of 16 nM (S/N = 3) and 91.53 μA μM−1, respectively, surpassing other modified electrodes. Moreover, these Re@CDACs catalysts were also found to exhibit a higher specific capacitance of 181 F g-1 at a current density of 1.6 A g−1 in 1.0 M H2SO4 electrolyte. The specific capacitance retention of 90% was achieved after 2500 cycles at current density 2.0 A g−1. Therefore, we have demonstrated that the Re@CDACs nanocomposite materials could be used as a promising electrode material in electrochemical oxidation of SY and energy storage applications. © 2018
Veerakumar, P, Tharini J, Ramakrishnan M, Panneer Muthuselvam I, Lin K-C.  2017.  Graphene Oxide Nanosheets as An Efficient and Reusable Sorbents for Eosin Yellow Dye Removal from Aqueous Solutions. ChemistrySelect. 2:3598-3607., Number 13 AbstractWebsite

In this study, 2D graphene oxide nanosheets (GONS) were synthesized and characterized by XRD, Raman, SEM, FE-SEM, TEM, XPS, TGA, UV-vis and FTIR spectral techniques. The efficiency of eosin yellow (EY) dye adsorption on the GONS under various experimental parameters such as contact time, pH and temperature was investigated. Adsorption kinetic data were characterized appropriately using pseudo second-order-kinetics and intraparticle diffusion methods. Free energy of adsorption (ΔG0), enthalpy (ΔH0), entropy (ΔS0) changes, activation energy and Arrhenius factors were also calculated. The endothermic and spontaneous nature of the adsorption process was confirmed by the positive value of the enthalpy change (ΔH0) and the negative value of free energy change (ΔG0). The adsorption mechanism was investigated by FTIR spectra of GONS before and after adsorption of EY dye molecules. The remarkable adsorption capacity of EY onto the GONS can be attributed to the various adsorption interaction mechanisms such as hydrogen bonding, π-π electron, and electrostatic interactions. The maximum adsorption capacity for EY was calculated to be 217.33 mg g-1. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Tsai, P-Y, Chao M-H, Kasai T, Lin K-C, Lombardi A, Palazzetti F, Aquilanti V.  2014.  Roads leading to roam. Role of triple fragmentation and of conical intersections in photochemical reactions: Experiments and theory on methyl formate. Physical Chemistry Chemical Physics. 16:2854-2865., Number 7 AbstractWebsite

The exploration of alternative roads that open to molecules with sufficient energy to yield different products permits prediction and eventually control of the outcomes of chemical reactions. Advanced imaging techniques for monitoring laser-induced photodissociation are here combined with dynamical simulations, involving ample sets of classical trajectories generated on a quantum chemical potential energy surface. Methyl formate, HCOOCH3, is photodissociated at energies near the triple fragmentation threshold into H, CO and OCH3. Images of velocity and rotational distributions of CO exhibit signatures of alternative routes, such as those recently designated as transition-state vs. roaming-mediated. Furthermore, a demonstration of the triple fragmentation route is given, and also confirmed by H-atom product imaging and FTIR time-resolved spectra of the intermediate HCO radical. In addition, the relevance of nonadiabatic transitions promoted by a conical intersection is clarified by simulations as the privileged "reactivity funnel" of organic photochemistry, whereby the outcomes of molecular photoexcitation are delivered to electronic ground states. This journal is © the Owner Societies 2014.
Kao, M-J, Chen C-H, Tsai P-Y, Lim T-S, Lin K-C, Luh T-Y.  2011.  Hydrogen-bonding-induced one-handed helical polynorbornenes appended with chiral alaninegland. Macromolecular Chemistry and Physics. 212:2328-2338., Number 21 AbstractWebsite

Polynorbornenes appended with anthracene and chiral alanine linkers are synthesized. Hydrogen bonding between the adjacent bisamidic linkers brings adjacent anthracene chromophores in a more suitable orientation for exciton coupling and renders one-handed helical structures for these polymers. Excimer formation is observed from their emission spectra. Monoamidic linkers provide only one hydrogen bond, which would be less robust and result in much lower circular dichroic response. Hydrogen bonding between the adjacent chiral alanine linkers brings appended anthracene in a more suitable orientation for exciton coupling and excimer formation, rendering one-handed helical structures in polynorbornenes. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Veerakumar, P, Salamalai K, Dhenadhayalan N, Lin K-C.  2019.  Catalytic Activity of Bimetallic (Ruthenium/Palladium) Nano-alloy Decorated Porous Carbons Toward Reduction of Toxic Compounds. Chemistry - An Asian Journal. 14(15):2662-2675. AbstractWebsite

Chicken feather-derived high-surface-area porous activated carbon (CFAC) material was prepared using chemical activation. A new composite composed of Ru-Pd nanoparticles supported on CFAC (Ru-Pd@CFAC) has been prepared by microwave-thermal reduction in the presence of the support. Characterization by XRD, Raman, BET, FE-SEM/TEM, FT-IR, TGA, XPS, HAADF-STEM-EDS, H2-chemisorption, H2-TPR, and ICP-AES was used to analyze the catalyst. This catalyst is found to be efficient for the reduction of hexavalent chromium (CrVI), potassium ferricyanide (K3[Fe(CN)6]), 4-nitrophenol (4-NP), and pendimethalin (PDM), at room temperature, and remains stable, even after several repeated runs. Moreover, it showed excellent catalytic activity compared with the monometallic counterparts. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Lin, K.-C., MCKCBH-P.  2021.  Halogen-related photodissociation in atmosphere: characterisation of atomic halogen, molecular halogen, and hydrogen halide. AbstractWebsite

Atomic halogen elimination from halogen-related compounds plays a vital role in the depletion of the ozone layer and is well investigated. However, the probabilities for elimination of molecular halogens and hydrogen halides are rarely scrutinised. We develop distinct method for the investigation of each kind of fragment. Velocity-mapping ion-imaging was employed to study the atomic halogen elimination from alkyl halides and aryl halides, focusing on the fractions of the translational energy release, the quantum yields of the atomic fragments, transition probability for curve crossing, competitive halogen-related bond fission, and anisotropy parameters to understand their dynamical complexity. Cavity ring-down absorption spectroscopy was implemented to investigate the molecular halogen fragments dissociated from the aliphatic halides and acyl halides for their optical spectra, vibrational branches, quantum yields, and the dissociation mechanisms. Time-resolved Fourier transform infrared emission spectroscopy was employed to confine the primary products of hydrogen halide elimination from acyl halides in the presence of Ar gas. It is, for the first time, to overview these existing small halogen-related fragments eliminated from halogen-containing compounds. The detailed characterisation of these fragments should unveil complicated halogen-related dissociation mechanisms which may supplement the current knowledge and help with the photochemical assessment of halogen-related environmental issue. © 2020 Informa UK Limited, trading as Taylor & Francis Group.
Dhenadhayalan, N, Lin T-W, Veerakumar P, Lin K-C.  2018.  Metal Nanoparticles Anchored on Rhenium Disulfide Nanosheets as Catalysts for the Reduction of Aromatic Nitro Compounds. ChemNanoMat. AbstractWebsite

Abstract The nanohybrids of noble metal (M=Ag, Au, Pd, Pt, and Ru) nanoparticle-decorated rhenium disulfide nanosheets (ReS2 NSs) were demonstrated as excellent catalysts towards the reduction of aromatic nitro compounds. The M/ReS2 nanohybrids were synthesized by facile hydrothermal method and characterization results proved that each metal nanoparticle was anchored on the ReS2 NSs. These nanohybrids exhibited superior catalytic performance towards the reduction of aromatic nitro compounds including 4-nitrophenol, 2-nitroaniline, and nitrobenzene. Interestingly, the Ru/ReS2 and Pd/ReS2 showed enhanced catalytic reduction compared to Ag/ReS2, Au/ReS2, and Pt/ReS2 and also showed significant catalytic stability due to metal nanoparticles anchored strongly on the surface of ReS2 NSs. Moreover, these M/ReS2 nanohybrids turned out to have much better catalytic performance compared to noble metal nanoparticle-based catalysts. A plausible reduction mechanism was proposed for each nitro compound. It was verified that the metal-nanoparticle-mediated hydrogen transfer was involved in the reduction of nitro compounds to amines. This report demonstrates the catalytic activities for metal nanoparticle-decorated ReS2 nanohybrids, which can serve as a paradigm to open up a future trend in the design of transition metal dichalcogenides nanohybrids as superior catalysts.