Browsing by Author "Raghunath, Putikam"

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A new pyrene-based aggregation induced ratiometric emission probe for selective detections of trivalent metal ions and its living cell application
(2015-02-01)
Singh, Ashutosh
;
Singh, Ravinder
;
Shellaiah, Muthaiah
;
Prakash, Epperla Chandra
;
Chang, Huan-Cheng
We synthesize a newly designed pyrene-based fluorescent probe FBP containing a Schiff base and amide linkage as a receptor, which demonstrates selective UV-vis and fluorometric detections of trivalent metal ions in various semi-aqueous solution conditions. Interestingly, by increasing water contents the aggregation induced ratiometric emissions (AIREs) of photoluminescence in FBP solutions (in DMSO/H2O) are enhanced from blue to green due to the excimer formation of the aggregates in water. In addition, the enhanced aggregated ratiometric green fluorescence behaviors of FBP in the presence of trivalent metal ions (Al3+, Fe3+, and Cr3+) are observed in semi-aqueous solutions as well as the solid state, which is well utilized to detect trivalent metal ions in living cells. Further verification of the probe detections, their interactions toward trivalent metal ions are well characterized by the time-resolved photoluminescence (TRPL) of spectroscopic responses as well as theoretical calculations. Therefore, we believe the application of such a new AIRE-based approach is first reported among Schiff base and pyrene-based fluorescentchemo- and bio-sensors. (C) 2014 Elsevier B.V. All rights reserved.
Ab initio chemical kinetics for hypergolic reactions of nitrogen tetroxide with hydrazine and methyl hydrazine
(2019-09-01)
Trinh Le Huyen
;
Raghunath, Putikam
;
Lin, M. C.
;
交大名義發表
;
應用化學系
The kinetics and mechanisms for the hypergolic reactions of N2O4 (NTO) with N2H4 and CH3NHNH2 have been investigated by ab initio molecular orbital theory based on the UCCSD(T) method with the 6-311 + G(3df, 2p) basis set. These reactions are important to the propulsion chemistry of the N2O4-N2H3X (X = H, CH3) propellant systems. The results of our calculations show that the hypergolic ignition reactions of NTO with N2H4 and CH3NHNH2, producing N2H3NO + HNO3 and CH3NHN(H)NO/CH3N(NO)NH2 + HNO3, respectively, can be initiated by the rapid attack of hydrazine molecules by ONONO2, following the isomerization of NTO via loose, roaming-like transition states with 5.9 and 6.3 kcal/mol above the reactants in the presence of the hydrazine reactants as spectators. The rate constants for the reactions have been predicted in the temperature range 298-2000 K with the transition state theory; the result indicates, for example, that the half-life of N2O4 at 300 K in a mixture containing an excess amount of N2H4 at atmospheric pressure was predicted to be as short as 1.4 x 10(-3) s; similarly, a 50-50 mixture of N2O4 and N2H4 at atmospheric pressure decays by half within 4.1 x 10(-5) s upon mixing at 300 K, both reflecting the very effective hypergolic initiation of these propellant systems.
Ab Initio Chemical Kinetics for Nitrogen Tetroxide Reactions with 1,1-and 1,2-Dimethylhydrazines
(1970-01-01)
Le Huyen, Trinh
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Raghunath, Putikam
;
Lin, Ming Chang
;
交大名義發表
;
應用化學系
This work employed the quantum-chemical method at the CCSD(T)/6-311+G(3df,2p)//B3LYP/6-311+G(3df,2p) level to study the mechanisms and kinetics of N2O4 (NTO) with H2NN(CH3)(2) and CH3NHNHCH3 hypergolic initiation reactions, the processes critical to the chemical rocket propulsion of the N2O4-hydrazine propellant systems. The reaction of N2O4 with the dimethylhydrazines (DMHZ's) can be started by the fast reaction of DMHZ's with ONONO2, taking place after the novel N2O4 -> ONONO2 transformation with each of DMHZ's as a spectator within the NTO-DMHZ collision complexes, through loose, roaming-like transition states during the bimolecular encounters. The barriers for such isomerization processes were found to be 7.2 and 9.9 kcal/mol for H2NN(CH3)(2) and CH3NHNHCH3, respectively. The kinetics of these reactions have been computed in the temperature range 200-2000 K; the results indicate that under the ambient temperature and pressure condition, the half-life of NTO in the presence of an excess amount of H2NN(CH3)(2) is predicted to be 3.3x10(-5) s. The results of a similar estimate for CH3NHNHCH3 is about 2 orders of magnitude longer; both estimates indicate that very effective hypergolic reactions can occur upon mixing in these systems.
Ab Initio Chemical Kinetics for Reactions of H Atoms with SiHx (x=1-3) Radicals and Related Unimolecular Decomposition Processes
(2013-06-15)
Raghunath, Putikam
;
Lee, Yun-Min
;
Wu, Shang-Ying
;
Wu, Jong-Shinn
;
Lin, Ming-Chang
Hydrogen atoms and SiHx (x = 1-3) radicals coexist during the chemical vapor deposition (CVD) of hydrogenated amorphous silicon (a-Si: H) thin films for Si-solar cell fabrication, a technology necessitated recently by the need for energy and material conservation. The kinetics and mechanisms for H-atom reactions with SiHx radicals and the thermal decomposition of their intermediates have been investigated by using a high high-level ab initio molecular-orbital CCSD (Coupled Cluster with Single and Double)(T)/CBS (complete basis set extrapolation) method. These reactions occurring primarily by association producing excited intermediates, (SiH2)-Si-1, (SiH2)-Si-3, SiH3, and SiH4, with no intrinsic barriers were computed to have 75.6, 55.0, 68.5, and 90.2 kcal/mol association energies for x = 1-3, respectively, based on the computed heats of formation of these radicals. The excited intermediates can further fragment by H-2 elimination with 62.5, 44.3, 47.5, and 56.7 kcal/mol barriers giving Si-1, Si-3, SiH, and (SiH2)-Si-1 from the above respective intermediates. The predicted heats of reaction and enthalpies of formation of the radicals at 0 K, including the latter evaluated by the isodesmic reactions, SiHx + CH4 SiH4 + CHx, are in good agreement with available experimental data within reported errors. Furthermore, the rate constants for the forward and unimolecular reactions have been predicted with tunneling corrections using transition state theory (for direct abstraction) and variational Rice-Ramsperger-Kassel-Marcus theory (for association/decomposition) by solving the master equation covering the P, T-conditions commonly employed used in industrial CVD processes. The predicted results compare well experimental and/or computational data available in the literature. (C) 2013 Wiley Periodicals, Inc.
Ab Initio Chemical Kinetics of Key Processes in the Hypergolic Ignition of Hydrazine and Nitrogen Tetroxide
(2014)
Raghunath, Putikam
;
Nghia, N. T.
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Lin, Ming-Chang
;
應用化學系
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Department of Applied Chemistry
Kinetics and mechanisms of key processes leading to the hypergolic ignition of N2H4 and N2O4 have been studied by high-level ab initio molecular orbital theory in conjunction with statistical theory calculations. The results of this work suggest that the explosion following the contact of N2H4 and N2O4 in liquid or gaseous state at low temperatures can be initiated by the rapid reaction of N2H4 with ONONO2 isomers of N2O4 producing H2NN(H)NO+HNO3 without thermal activation accompanying with 21 kcal mol(-1) exothermicity. The HNO3 thus formed can instantaneously produce [N2H5+]NO3-] salt releasing twice as much acid base neutralization energy to enhance NO2 and N2H3 radical production. The thermochemistry and rate constants for reactions of species involved (NO2, NO3, N2O4, and its isomers, OH and N2Hx,(x= 2, 3, and 4)) in the chain initiation and propagation have been predicted and compared with available data in the literature.
Controlled Sol-Gel and Diversiform Nanostructure Transitions by Photoresponsive Molecular Switching of Tetraphenylethene- and Azobenzene-Functionalized Organogelators
(2020-07-01)
Arumugaperumal, Reguram
;
Hua, Wei-Ling
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Raghunath, Putikam
;
Lin, Ming-Chang
;
Chung, Wen-Sheng
The implementation of stimuli-responsive materials with dynamically controllable features has long been an important objective that challenges chemists in the materials science field. We report here the synthesis and characterization of [2]rotaxanes (R1 and R1-b) with a molecular shuttle and photoresponsive properties. Axles T1 and T1-b were found to be highly efficient and versatile organogelators toward various nonpolar organic solvents, especially p-xylene, with critical gelation concentrations as low as 0.67 and 0.38 w/v %, respectively. The two molecular stations of switchable [2]rotaxanes (R1 and R1-b) can be revealed or concealed by t-butylcalix[4]arene macrocycle, thus inhibiting the gelation processes of the respective axles T1 and T1-b through the control of intermolecular hydrogen-bonding interactions. The sol-gel transition of axles T1 and T1-b could be achieved by the irradiation of UV-visible light, which interconverted between the extended and contracted forms. Interestingly, the morphologies of organogels in p-xylene, including flakes, nanobelts, fibers, and vesicles depending on the molecular structures of axles T1 and T1-b, were induced by UV-visible light irradiation. Further studies revealed that acid-base-controllable and reversible self-assembled nanostructures of these axle molecules were mainly constructed by the interplay of multi-noncovalent interactions, such as intermolecular pi-pi stacking, CH-pi, and intermolecular hydrogen-bonding interactions. Surprisingly, our TPE molecular systems (R1, R1-b, T1, and T1-b) are nonemissive in their aggregated states, suggesting that not only fluorescence resonance energy transfer but also aggregation-caused quenching may have been functioning. Finally, the mechanical strength of these organogels in various solvents was monitored by rheological experiments.
Development of Hybrid Pseudohalide Tin Perovskites for Highly Stable Carbon-Electrode Solar Cells
(2020-05-13)
Rameez, Mohammad
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Lin, Eric Yan-Ru
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Raghunath, Putikam
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Narra, Sudhakar
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Song, Donghoon
Tin-based perovskites degrade rapidly upon interaction with water and oxygen in air because Sn-I bonds are weak. To address this issue, we developed novel tin perovskites, FASnI((3-x))(SCN)(x) (x = 0, 1, 2, or 3), by employing a pseudohalide, thiocyanate (SCN-), as a replacement for halides and as an inhibitor to suppress the Sn2+/Sn4+ oxidation. The structural and electronic properties of pseudohalide tin perovskites in this series were explored with quantum-chemical calculations by employing the plane-wave density functional theory (DFT) method; the corresponding results are consistent with the experimental results. Carbon-based perovskite devices fabricated with tin perovskite FASnI(SCN)(2) showed about a threefold enhancement of the device efficiency (2.4%) relative to that of the best FASnI(3)-based device (0.9%), which we attribute to the improved suppression of the formation of Sn4+, retarded charge recombination, enhanced hydrophobicity, and stronger interactions between Sn and thiocyanate for FASnI(SCN)(2) than those for FASnI(3). After the incorporation of phenylethyleneammonium iodide (PEAI, 10%) and ethylenediammonium diiodide (EDAI(2), 5%) as coadditives, the FASnI(SCN)(2) device gave the best photovoltaic performance with J(SC) = 20.17 mA cm(-2), V-OC = 322 mV, fill factor (FF) = 0.574, and overall efficiency of power conversion PCE = 3.7%. Moreover, these pseudohalide-containing devices display negligible photocurrent-voltage hysteresis and great stability in ambient air conditions.
Development of Novel Mixed Halide/Superhalide Tin-Based Perovskites for Mesoscopic Carbon-Based Solar Cells
(2020-04-02)
Rameez, Mohammad
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Shahbazi, Saeed
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Raghunath, Putikam
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Lin, Ming Chang
;
Hung, Chen Hsiung
Tin perovskites suffer from poor stability and a self-doping effect. To solve this problem, we synthesized novel tin perovskites based on superhalide with varied ratios of tetrafluoroborate to iodide and implemented them into solar cells based on a mesoscopic carbon-electrode architecture because film formation was an issue in applying this material for a planar heterojunction device structure. We undertook quantum-chemical calculations based on plane-wave density functional theory (DFT) methods and explored the structural and electronic properties of tin perovskites FASnI(3-x)(BF4)(x) in the series x = 0, 1, 2, and 3. We found that only the x = 2 case, FASnI(BF4)(2), was successfully produced, beyond the standard FASnI(3). The electrochemical impedance and X-ray photoelectron spectra indicate that the addition of tin tetrafluoroborate instead of SnI2 suppressed trap-assisted recombination by decreasing the Sn4+ content. The power conversion efficiency of the FASnI(BF4)(2) device with FAI and Sn(BF4)(2) in an equimolar ratio improved 72% relative to that of a standard FASnI(3) solar cell, with satisfactory photostability under ambient air conditions.
Distinct Nanostructures and Organogel Driven by Reversible Molecular Switching of a Tetraphenylethene-Involved Calix[4]arene-Based Amphiphilic [2]Rotaxane
(2018-10-23)
Arumugaperumal, Reguram
;
Raghunath, Putikam
;
Lin, Ming-Chang
;
Chung, Wen-Sheng
;
應用化學系
Aggregation induced emission (AIE) active and acid/base controllable amphiphilic [2]rotaxanes R1 and R2 were successfully constructed with tetraphenylethene (TPE) as a stopper and t-butylcalix[4]arene or calix[4]arene macrocycle as a wheel over the axle component. The AIE effect of [2]rotaxanes R1 and R2 was greatly affected by the molecular shuttling of t-butylcalix[4]arene or calix[4]arene macrocycle, which was triggered by the acid/base strategy. In the case of [2]rotaxane R1, aggregation was achieved in the presence of less amount of water compared with those of [2]rotaxane R2, and the deprotonated [2]rotaxanes R1-b and R2-b, owing to the stronger interaction between the TPE and t-butylcalix[4]arene macrocycle and restricted intramolecular rotation (RIR), thus making it responses in less quantity of water along with highly fluorescent emission. [2]Rotaxane R1-b started to aggregate at 70% water fraction (f(w)), while [2]rotaxane R2-b started to aggregate at 75% f(w) which allowed them to morph into hollow nanospheres, whereas they formed only nanospheres at 99% f(w) in CH3CN/water cosolvent system due to the higher degree of aggregation in aqueous media. To our delight, controllable morphology of self-assembled structures was indeed formed from these [2]rotaxanes. Interestingly, by the interplay of a wide range of multi-self-assembly driving forces, the slack stacking of rotaxane unit forms a hollow on the surface of nanospheres to become hollow nanospheres. Among the four [2]rotaxanes studied here, R1 possessed a narrower HOMO-LUMO band gap compared to those others, as confirmed by computational study. Furthermore, only [2]rotaxane R1 formed organogel in methanol solvent and its reversible gel-sol transition could be achieved by the addition of acid and base. This implies that the formation of dumbbell shape cross-linked 3D network structures were mainly governed by pi-pi stacking, van der Waals force, and intermolecular H-bonding interactions during the gelation processes.
Effective hydrogenation of TiO2 photocatalysts with CH3OH for enhanced water splitting: A computational and X-ray study
(2019-09-15)
Wang, Tsai-Te
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Raghunath, Putikam
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Lin, Yu-Chang
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Lin, Yan-Gu
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Lin, Ming-Chan
We have investigated computationally and experimentally the efficacy of CH3OH treatment of anatase TiO2 nanoparticles (NPs) and compared the results obtained with H-2 as the hydrogenation source. The results indicate that TiO2 NPs heated at 300 degrees C in 120 Torr of CH3OH vapor is more effective than the samples heated under 800 Torr of H-2 at the same temperature. Ultraviolet-visible spectroscopy (UV-VIS), Photoluminescence spectroscopy (PL) and X-ray diffraction spectroscopy (XRD) were employed to study the optical property. The effect of temperature of hydrogenation has been systematically studied for NPs in the 200-450 degrees C range for both H-sources based on H-2 evolution, employing Xe lamp as the light source. The hydrogenated TiO2 NPs using H-2 and CH3OH have been analyzed by soft X-ray absorption near-edge structure analyses with and without Xe lamp irradiation in situ. The result indicates that CH3OH hydrogenation can induce a much stronger Ti-O interaction along direction d(z)(2) and increase the unoccupied DOS of Ti t(2g) states. This is why the CH3OH treated TiO2 exhibits a greater photo-activity. The crucial role of the hydrogenation using CH3OH was also investigated systematically and confirmed by quantum-chemical calculations with complementary synchrotron-based X-ray techniques. The results are consistent with the predicted barriers for the formation of H atoms on the TiO2 surface, 4-9 kcal/mol, considerably lower than that in the H-2 case, 48 kcal/mol.
Hydrogen-bonded effects on supramolecular blue phase liquid crystal dimeric complexes
(2015-01-01)
Wei, Chong-Lun
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Chen, Te-Cheng
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Raghunath, Putikam
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Lin, Ming-Chang
;
Lin, Hong-Cheu
In this study, a series of novel asymmetric hydrogen-bonded (H-bonded) dimeric complexes D/P and D/P* (proton donors D = A, A*, AF and AF*) were synthesized and self-assembled by appropriate molar ratios of H-donors (A, A*, AF and AF*) and H-acceptors (P and P*). In addition, the influences of the lateral fluoro-substituent of H-donors, the number (along with the position) of chiral centers and the molar ratio of H-donors and H-acceptors on the mesophasic behaviours (e.g., BPs) of asymmetric H-bonded dimeric complexes are investigated. Interestingly, the blue phase (i.e., BPI) was observed in complexes A*/P, A*/P*, AF*/P and AF*/P* containing at least a chiral center in H-donors (A* and AF*), including the widest BPI ranges of complexes AF*/P* (ca. 6 degrees C and 13 degrees C for 1 : 1 and 3 : 1 mol, respectively). For the first time, the hydrogen-bonded effects on supramolecular blue phase LCs are compared with their analogous covalent diads. Based on our theoretical calculation, we discovered that the bend angle plays an important role in manipulating the existence of the blue phase, which is preferred to appear at the bend angle within 132.1-152.9 degrees. Hence, owing to inappropriate bend angles, both H-bonded dimeric complex A/P* and covalent diad A*-P (with bend angles of 162.0 degrees and 126.5 degrees, respectively) did not possess any blue phase.
Isomerization of N2O4 in Solid N2H4 and Its Implication for the Explosion of N2O4-N2H4 Solid Mixtures
(2018-10-18)
Raghunath, Putikam
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Lin, M. C.
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交大名義發表
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National Chiao Tung University
The mechanism responsible for the explosion of solid mixtures of nitrogen tetroxide (N2O4) and hydrazine (HZ) or methyl-substituted HZs, detected experimentally by slow warming from 77 to 203-223 K, has been elucidated by quantum chemical calculations using the Vienna ab initio simulation package code. The result of the calculation for the reaction of a N2O4 molecule embedded in the middle of the N2H4 molecular crystal, N2O4@HZ(23), indicates that a loose nonconventional transition state (TS) occurring by stretching the O2N-NO2 bond up to 2.18 A with the concerted rotation of one of the NO2 groups producing the reactive ONONO2 isomer (ONONO2@HZ(23)) has a low 13.1 kcal/mol barrier at TS1; the process is exothermic by 45 kcal/mol, reflecting the much stronger ONONO2 binding with N2H4. A further simultaneous reaction of ONONO2 with 2N(2)H(4) in the same unit cell occurs with a small 1.4 kcal/mol barrier producing NO3- + NH2N(H)NO + N2H5+ with an overall exothermicity of 70.2 kcal/mol. The mechanism for this last-step reaction is distinctly different from that in the gas phase taking place via a five-centered concert mechanism giving N2H3NO and HNO3, which can further produce N2H5+NO3- by the rapid acid-base neutralization process. On the basis of the predicted structure, energy, and vibrational frequencies at TS1, we estimated the rate constant at 218 K for the N2O4-ONONO2 isomerization reaction in solid N2H4 to be 1.35 s(-1), giving the half-life of N2O4 @HZ 23 to be as short as 0.5 s. This result can explain why the slow warming of the solid mixtures of N2O4 and N2H4 from 77 K exploded reproducibly at 218 K.
KSCN-induced Interfacial Dipole in Black TiO2 for Enhanced Photocatalytic CO2 Reduction
(2019-07-17)
Fu, Fang-Yu
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Shown, Indrajit
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Li, Chia-Shuo
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Raghunath, Putikam
;
Lin, Tsai-Yu
Tuning the electronic band structure of black titania to improve photocatalytic performance through conventional band engineering methods has been challenging because of the defect-induced charge carrier and trapping sites. In this study, KSCN-modified hydrogenated nickel nano cluster-modified black TiO2 (SCN-H-Ni-TiO2) exhibits enhanced photocatalytic CO2 reduction due to the interfacial dipole effect. Upon combining the experimental and theoretical simulation approach, the presence of an electrostatic interfacial dipole associated with chemisorption of SCN has dramatic effects on the photocatalyst band structure in SCN H-Ni-TiO2. An interfacial dipole possesses a more negative zeta potential shift of the isoelectric point from 5.20 to 3.20, which will accelerate the charge carrier separation and electron transfer process. Thiocyanate ion passivation on black TiO2 demonstrated an increased work function around 0.60 eV, which was induced by the interracial dipole effect. Overall, the SCN H-Ni-TiO2 photocatalyst showed an enhanced CO2 reduction to solar fuel yield by 2.80 times higher than H-Ni-TiO2 and retained around 88% product formation yield after 40 h.
Lateral fluoro-substitution and chiral effects on supramolecular liquid crystals containing rod-like and H-bonded bent-core mesogens
(2016-01-01)
Han, Chun-Chieh
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Yang, Li-Han
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Raghunath, Putikam
;
Lin, Ming-Chang
;
Kumar, Rohit
The first series of liquid crystalline supramolecular diads C/D containing asymmetric rod-like and H-bonded bent-core mesogens were designed and synthesised, among which supramolecular diad P*(III)/A*(II) with two chiral centers on both the H-acceptor/H-donor and non-lateral fluoride substitution possessed a wide blue phase (BPI) range of 13.7 degrees C. According to the molecular modeling, a large biaxial parameter (>= 3.2) and an appropriate HTP value (4.2-4.8 mu m(-1)) are the most important factors to stabilize the double twisted cylinder structure (i.e., BPI) in supramolecular diads. Moreover, the bent angles, biaxial parameters and dipole moments of supramolecular diads are mainly affected by the locations and numbers of H-bonds and chiral centers. Not only larger bent angles and biaxial parameters but also smaller dipole moments and HTP values were obtained by removing the lateral fluoride substitution on supramolecular diads to achieve the blue phase of P*(III)/A*(II) (without lateral fluoride substitution). Finally, the special optimal 1 : 1 molar ratio of supramolecular diad P*(III)/A*(II) (i.e., H-donor = 50 mol%) with the widest blue phase range is mainly attributed to its rod-like and H-bonded bent-core mesogens, rather than H-donor = 75 mol% in most supramolecular complexes containing linear H-bonded rod-like mesogens.
Linear solubilizing side chain substituents enhance the photovoltaic properties of two-dimensional conjugated benzodithiophene-based polymers
(2015-11-19)
Jiang, Jian-Ming
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Raghunath, Putikam
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Lin, Yu-Che
;
Lin, Hsi-Kuei
;
Ko, Chen-Lin
In this study we synthesized medium-band gap, two-dimensional (2-D) conjugated polymers comprising electron-rich benzo[1,2-b:4,5-b\'] dithiophene (BDT) units presenting conjugated thiophene (T) side chains and electron-deficient alkoxy-modified 2,1,3-benzooxadiazole (BO) moieties. We introduced various solubilizing substituents-linear alkyl, alkoxy, and alkythio units-on the thiophene side chains to obtain a series of 2-D conjugated D-pi-A polymers: PBDTT-C-BO, PBDTT-O-BO, and PBDTT-S-BO. The solubilizing substituents of the BDT units altered the solubility, conformations, and electronic properties of the synthesized conjugated polymers, allowing tuning of the photovoltaic properties when blended with fullerenes. We investigated the effects of the different linear solubilizing substituents of the BDT units on the structural, optical, and electronic properties (e.g., band gap energies) of the resulting 2-D conjugated polymers, as determined from quantum-chemical calculations, UV-Vis absorption spectra, and grazing-incidence X-ray diffraction. Atomic force microscopy and transmission electron microscopy images revealed the morphologies of active layers comprising these 2-D conjugated polymers and the fullerene derivative [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM). Through rational structural modifications of the solubilizing substituents in the 2-D conjugated polymers with alkoxy, alkythio or alkyl units, the resulting PCEs varied from 5.4 to 7.5%. A polymer solar cell based on a blend of PBDTT-C-BO and PC71BM exhibited the best photovoltaic performance among our three studied systems, with a high short-circuit current density (J(sc)) of 15.7 mA cm(-2) and a power conversion efficiency of 7.5%, without the need for any processing additives or post-treatment processes, highlighting the importance of careful selection of appropriate solubilizing substituent that attached to the donor segments when designing efficient D-pi-A polymers for use in solar cells. (C) 2015 Elsevier Ltd. All rights reserved.
Location and Number of Selenium Atoms in Two-Dimensional Conjugated Polymers Affect Their Band-Gap Energies and Photovoltaic Performance
(2014-10-28)
Jiang, Jian-Ming
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Raghunath, Putikam
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Lin, Hsi-Kuei
;
Lin, Yu-Che
;
Lin, M. C.
We synthesized and characterized a series of novel two-dimensional Se-atom-substituted donor (D)-p-acceptor (A) conjugated polymersPBDTTTBO, PBDTTTBS, PBDTTSBO, PBDTSTBO, PBDTTSBS, PBDTSTBS, PBDTSSBO, and PBDTSSBSfeaturing benzodithiophene (BDT) as the donor, thiophene (T) as the p-bridge, and 2,1,3-benzooxadiazole (BO) as the acceptor with different number of Se atoms at different p-conjugated locations, including the pi-bridge, side chain, and electron-withdrawing units. We then systematically investigated the effect of different locations and the number of Se atoms in these two-dimensional conjugated polymers on the structural, optical, and electronics such as band-gap energies of the resulting polymers, as determined through quantum-chemical calculations, UVvis absorption spectra, and grazing-incidence X-ray diffraction. We found that through the rational structural modification of the 2-D conjugated Se-substituted polymers the resulting PCEs could vary over 3-fold (from 2.4 to 7.6%), highlighting the importance of careful selection of appropriate chemical structures such as the location of Se atoms when designing efficient D-p-A polymers for use in solar cells. Among these tested BO-containing polymers, PBDTSTBO that has moderate band gaps and good open-circuit voltages (up to 0.86 V) when mixed with PC71BM (1:2, w/w) provided the highest power conversion efficiency (7.6%) in a single-junction polymer solar cell, suggesting that these polymers have potential applicability as donor materials in the bulk heterojunction polymer solar cells.
Monomeric and aggregation emissions of tetraphenylethene in a photo-switchable polymer controlled by cyclization of diarylethene and solvent conditions
(2017-10-14)
Singh, Ravinder
;
Wu, Hsin-Yen
;
Dwivedi, Atul Kumar
;
Singh, Ashutosh
;
Lin, Chien-Min
A novel photo-switchable polymer P-PHT containing diarylethene (DAE) and tetraphenylethene (TPE) moieties and a triazole linker in the repeating unit was synthesized to study the aggregation-induced emission (AIE) behaviour of TPE with both the open and closed forms of DAE in P-PHT with high water contents. The photo-switching phenomena of DAE (from open to closed forms under UV-irradiation) in P-PHT were prominent in organic solvent (THF), high water contents (at 90% H2O) and acidic conditions. Upon UV-irradiation of P-PHT at 90% water content, the AIE of TPE was completely quenched via an energy transfer event from TPE to cyclized DAE. Interestingly, the rare monomeric emission of TPE was first discovered by the photo-cyclization of DAE in P-PHT compared with the AIE behaviour of TPE with the open form of DAE in P-PHT with AIE favourable conditions of high water content (90% H2O) and acidic conditions.
Multi-stimuli-responsive high contrast fluorescence molecular controls with a far-red emitting BODIPY-based [2]rotaxane
(2018-10-01)
Arumugaperumal, Reguram
;
Venkatesan, Parthiban
;
Shukla, Tarun
;
Raghunath, Putikam
;
Singh, Ravinder
A novel fluorescent switchable [2]rotaxane NIR4 composed of two different molecular stations and rotaxane arms terminated with far-red boron-dipyrromethene (BODIPY) fluorophores and its derivatives were synthesized by CuAAC click chemistry. The molecular shuttling motion of mechanically interlocked molecules (MIMs) could be addressed by the fluorescence signal transduction via distance dependent photo-induced electron transfer process of [2]rotaxane NIR4 triggered by external chemical stimuli of acid/base. Moreover, the flexible arms of triazolium moiety in [2]rotaxane NIR4 and its axle NIR2 exhibited impressive selectivity and sensitivity toward complementary anionic analyte (H2PO4-), where the specific mechanical molecular motion was supported by quantum mechanical calculations. The development of [2]rotaxane NIR4 with a high level of structural complexity can be utilized for novel dual sensory detections of acid-base and dihydrogen phosphate (H2PO4-) anion. Importantly, the host of NIR2 and [2]rotaxane NIR4 could be applied for the vitro imaging and clarify the distribution of H2PO4- at subcellular levels.
Ni-Nanocluster Modified Black TiO2 with Dual Active Sites for Selective Photocatalytic CO2 Reduction
(2018-01-11)
Billo, Tadesse
;
Fu, Fang-Yu
;
Raghunath, Putikam
;
Shown, Indrajit
;
Chen, Wei-Fu
One of the key challenges in artificial photosynthesis is to design a photocatalyst that can bind and activate the CO2 molecule with the smallest possible activation energy and produce selective hydrocarbon products. In this contribution, a combined experimental and computational study on Ni-nanocluster loaded black TiO2 (Ni/TiO2[Vo]) with built-in dual active sites for selective photocatalytic CO2 conversion is reported. The findings reveal that the synergistic effects of deliberately induced Ni nanoclusters and oxygen vacancies provide (1) energetically stable CO2 binding sites with the lowest activation energy (0.08 eV), (2) highly reactive sites, (3) a fast electron transfer pathway, and (4) enhanced light harvesting by lowering the bandgap. The Ni/TiO2[Vo] photocatalyst has demonstrated highly selective and enhanced photocatalytic activity of more than 18 times higher solar fuel production than the commercial TiO2 (P-25). An insight into the mechanisms of interfacial charge transfer and product formation is explored.
Novel asymmetrical single- and double-chiral liquid crystal diads with wide blue phase ranges
(2015-01-01)
Wei, Chong-Lun
;
Chen, Te-Cheng
;
Raghunath, Putikam
;
Lin, Ming-Chang
;
Lin, Hong-Cheu
In this study, two series of novel asymmetrical single- and double-chiral liquid crystal diads using a central linker to link two different mesogenic cores were successfully synthesized. The effects of the position of chiral centers and the number of aromatic rings on the mesomorphic and electro-optical properties were investigated. We found that diads III-N (where N = A, B, C and D) have better mesophasic properties than II-N (where N = A, B, C, D and E). Compared with III-C with a chiral center at the terminal alkoxyl chain, diad III-D exhibited the widest temperature range of BPI (ca. 31 degrees C) as the chiral center was introduced to the central linker. Besides III-D, BPs were also observed in diads II-B and III-B with a chiral center at the central spacer. According to our experimental results and molecular modeling, the mesomorphic properties and temperature ranges of BPs will be affected by the values of biaxiality and dipole moment, along with the bent shape of molecular geometry. Therefore, we demonstrated the first example of asymmetrical single- and double-chiral liquid crystal diads involved chiral centers located at the central linker to exhibit BPs, including the mesophases of BPI and BPIII, which might offer new BP single-components to the future applications of eutectic liquid crystal mixtures with wide BP ranges.