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Öğe Carbazole based D-A-pi-A chromophores for dye sensitized solar cells: Effect of the side alkyl chain length on device performance(Pergamon-Elsevier Science Ltd, 2017) Kiymaz, Deniz; Sezgin, Meryem; Sefer, Emre; Zafer, Ceylan; Koyuncu, SermetA series of Carbazole based Donor-Acceptor-pi Bridge-Acceptor (D-A-pi-A) dyes that contain different alkyl side chains with different lengths have been synthesized. Electrochemical and optical properties of these dyes were demonstrated by impedance spectroscopy, cyclic voltammetry, UV-Vis absorption and fluorescence spectroscopy, respectively. Herein, we report PV performance of dye-sensitized solar cells depending on the molecular structure of the dyes in terms of comparison of alkyl chain length on the carbazole moiety using an ionic liquid based electrolyte under standard AM 1.5 illumination. The results demonstrate that the dye containing alkyl chain with 4C atoms exhibited better performance compared to alkyl chains with 2C, 6C and 12C atoms. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe A Concept for Dopant-Free Hole Transport Layers for Efficient and Stable New-Generation Perovskite Solar Cells(Amer Chemical Soc, 2024) Akin Kara, Duygu; Turgut, Sevdiye Basak; Cirak, Dilek; Karaman, Merve; Can, Mustafa; Koyuncu, Sermet; Gultekin, BurakA new donor-acceptor type polymers containing benzothiadiazole (HB1) and benzoselenidiazole (HB2) as acceptor units were prepared or use as hole transport layers in perovskite solar cells (PSCs). It was observed that the electrochemical HOMO-LUMO band gap narrowed from 2.74 to 1.88 depending on the variation in the acceptor unit. In addition, the charge-transfer band at 580 nm undergoes a 30 nm red-shift and broadens to the near-infrared region. HB1 and HB2 were introduced as dopant-free HTMs to replace the commonly used 2,2 ',7,7 '-tetrakis[N,N-di(4-methoxyphenyl)amino]-9-9 '-spirobifluorene (spiro-OMeTAD) in planar heterojunction n-i-p type of PSCs. Compared with HB2, HB1 exhibited better film morphology and mobility, resulting in improved charge-carrier extraction and transport. Dopant-free HB1 devices fabricated using the Cs0.05FA0.79MA0.16-Pb (IxBr1-x)3 triple cation perovskite displayed a champion power conversion efficiency of 11.69% under one sun illumination (100 mW cm(-2)) which is higher than the efficiency of HB2-based devices. The inflated performance was attributed to the reduced charge recombination and improved conductivity. In addition, these new HTMs exhibited higher hydrophobicity and thermal stability than their doped spiro-OMeTAD counterpart, making it possible to achieve good stability.Öğe Effect of a pi-bridging unit in triphenylamine-benzothiadiazole based donor acceptor chromophores for dye-sensitized solar cells(Pergamon-Elsevier Science Ltd, 2014) Yigit, Mesude Zeliha; Bilgili, Hakan; Sefer, Emre; Demic, Serafettin; Zafer, Ceylan; Can, Mustafa; Koyuncu, SermetTwo new metal free sensitizers based on triphenylamine-benzothiadiazole were synthesized and used in dye sensitized solar cells (DSSCs). Electrochemical and optical properties of the dyes were studied by cyclic voltammetry, UV-vis absorption and fluorescence spectroscopy. A red shift was observed by the attachment of a thiophene (MZ-259) instead of a phenylene (MZ-255) bridge. The reverse effect was observed in the electrochemical properties because of the more electron-donating thiophene incorporated into the cyanoacrylic acid as an anchoring-acceptor unit in this system resulted in a higher LUMO level. The charge distribution of the dyes was also proved by DFT calculations using the Spartan10 program with the parameters of B3LYP and 6-31G** basis set. Finally the photovoltaic performances were investigated under standard AM 1.5 illumination with a power of 100 mW/cm(2) using an ionic liquid based electrolyte. The power conversion efficiencies, eta, were increased from 3.16% to 3.81% by using thiophene instead of phenylene as a pi-bridge unit. (C) 2014 Elsevier Ltd. All rights reserved.Öğe Electrochemical and optical properties of biphenyl bridged-dicarbazole oligomer films: Electropolymerization and electrochromism(Pergamon-Elsevier Science Ltd, 2009) Koyuncu, Sermet; Gultekin, Burak; Zafer, Ceylan; Bilgili, Hakan; Can, Mustafa; Demic, Serafettin; Kaya, Ismet; Icli, Siddik4,4'-Di(N-carbazoyl)biphenyl monomer (CBP) was synthesized and coated onto ITO-glass surface by electrochemical oxidative polymerization. Its CV shows two distinct one-electron and stepwise oxidation processes occurred at 1.29 and 1.61 V. By using this property, the monomer was electrochemically polymerized separately at these oxidation states and thus, two different oligomer films were obtained afterwards. Their spectro-electrochemical and electrochromic properties were also investigated. Switching ability of the oligomers was evaluated by kinetic studies upon measuring the percent transmittance (%T) at their maximum contrast point, indicating that these oligomers were found to be suitable material for electrochromic devices. (C) 2009 Elsevier Ltd. All rights reserved.Öğe Electrochemical and optical properties of biphenyl bridged-dicarbazole oligomer films: Electropolymerization and electrochromism(Pergamon-Elsevier Science Ltd, 2009) Koyuncu, Sermet; Gultekin, Burak; Zafer, Ceylan; Bilgili, Hakan; Can, Mustafa; Demic, Serafettin; Kaya, Ismet; Icli, Siddik4,4'-Di(N-carbazoyl)biphenyl monomer (CBP) was synthesized and coated onto ITO-glass surface by electrochemical oxidative polymerization. Its CV shows two distinct one-electron and stepwise oxidation processes occurred at 1.29 and 1.61 V. By using this property, the monomer was electrochemically polymerized separately at these oxidation states and thus, two different oligomer films were obtained afterwards. Their spectro-electrochemical and electrochromic properties were also investigated. Switching ability of the oligomers was evaluated by kinetic studies upon measuring the percent transmittance (%T) at their maximum contrast point, indicating that these oligomers were found to be suitable material for electrochromic devices. (C) 2009 Elsevier Ltd. All rights reserved.Öğe Electrochemical and optical properties of novel donor-acceptor thiophene-perylene-thiophene polymers(John Wiley & Sons Inc, 2008) Koyuncu, Sermet; Kus, Mahmut; Demic, Serafettin; Kaya, Ismet; Ozdemir, Eyup; Icli, SiddikIn this study, donor-acceptor type thiophene-perylene-thiophene monomers were synthesized and polymerized by both oxidative polymerization using FeCl3 as catalyst and the electrochemical process. UV-vis, FTIR, H-1 NMR, and elemental analysis techniques were used for structural characterization. Thermal behaviors of these compounds were determined by using TGA system. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels and electrochemical and optical band gap values were calculated by using the results of cyclic voltammetry and UV-vis measurements, respectively. The number-average molecular weight (M-n), weight-average molecular weight (M-n), and polydispersity index (PDI) values of synthesized polymers were determined by size exclusion chromatography. Conductivity measurements of these polymers were carried out by electrometer by using a four-point probe technique. The conductivity was observed to be increased by iodine doping. (C) 2008 Wiley Periodicals, Inc.Öğe Electrochromic and electroluminescent devices based on a novel branched quasi-dendric fluorene-carbazole-2,5-bis(2-thienyl)-1H-pyrrole system(Royal Soc Chemistry, 2011) Koyuncu, Sermet; Usluer, Ozlem; Can, Mustafa; Demic, Serafettin; Icli, Siddik; Sariciftci, Niyazi SerdarWe report here the synthesis of a novel branched quasi-dendric system, 9,9'-(9,9'-dihexylfluorene-2,7-diyl)bis[3,6-bis(2,5-bis(2-thienyl) pyrrol-1-yl)carbazole], (FCSNS), in four steps, followed by coating onto an ITO-coated glass surface by an electropolymerization process to give a very stable cross-linked polymeric film (poly-FCSNS). The yellowish-green color of this film in its neutral state changed reversibly to black upon oxidation. An electrochromic device, assembled in the sandwich configuration [ITO/anodically coloring polymer (poly-FCSNS)//gel electrolyte//cathodically coloring polymer/(PEDOT)/ITO], exhibited a relatively short response time (about 1 s), a high redox stability, and a high coloration efficiency (1624 cm(2) C-1). In addition to electrochromic studies, organic light-emitting diode (OLED) work was also carried out using FCSNS. A multilayer OLED having a configuration of ITO/PEDOT:PSS/FCSNS/Alq(3)/LiF : Al was fabricated, and it showed a turn-on voltage of approximately 6 V and exhibited a bright green emission with a luminance of 3700 cd m(-2). The maximum luminous efficiency was found to be 2.0 cd A(-1) at 14 V and 11.75 mA cm(-2). The emitted light from the OLED device is green, and has the color coordinates of (x, y) (0.33, 0.54) according to CIE. Electrochemical and optical properties were also studied by using cyclic voltammetry, UV-Vis absorption and fluorescence spectroscopy, respectively.Öğe Highly conjugated isoindigo and quinoxaline dyes as sunlight photosensitizers for onium salt-photoinitiated cationic polymerization of epoxy resins(Wiley, 2022) Ercan, Bahar T.; Gultekin, Sirin S.; Yesil, Tamer; Dincalp, Haluk; Koyuncu, Sermet; Yagci, Yusuf; Zafer, CeylanIn this study, photoinitiated cationic polymerization of epoxy resins by photoinduced electron transfer reactions using four new chromophoric dyes, namely (3E)-1,1 '-bis(2-ethylhexyl)-6,6 '-dipyren-1-yl-3,3 '-biindole-2,2 '(1H,1 ' H)-dione (ISOIV), (3 ' E)-1,1 '''-diethyl-1 ',1 ''-bis(2-ethylhexyl)-1H,1 ''' H-5,6 ':3 ',3 '':6 '',5 '''-quaterindole-2 ',2 ''(1 ' H,1 '' H)-dione (ISOV), (3E)-6,6 '-bis(9-ethyl-9H-carbazole-3-yl)-1-[(2R)-2-ethylhexyl]-1 '-[(2S)-2-ethylhexyl]-3,3 '-biindole-2,2 '(1H,1 ' H)-dione (ISOVIII) and 3,3 '-(6-bromokinoksalin-2,3-diyl)bis(9-ethyl-9H-carbazole) (TPDC6), and diphenyliodonium hexafluorophosphate (Ph2I+PF6-; DPI) under sunlight is reported. Upon irradiation, photoexcited dye forms an exciplex with DPI. Electron transfer reactions within the exciplex result in the formation of ionic species capable of initiating ring-opening polymerization of an epoxy resin. It is shown that among the investigated dyes, ISOVIII and TPDC6 exhibited higher initiation efficiency in accordance with their stronger electron-donating nature due to the presence of carbazole groups. (c) 2021 Society of Industrial Chemistry.Öğe A narrow range multielectrochromism from 2,5-di-(2-thienyl)-1H-pyrrole polymer bearing pendant perylenediimide moiety(Elsevier Sci Ltd, 2015) Sefer, Emre; Bilgili, Hakan; Gultekin, Burak; Tonga, Murat; Koyuncu, SermetA new 2,5-di-(2-thienyl)-1H-pyrrole (SNS) moiety containing perylenediimide (PDI) acceptor as pendant side chain has been synthesized for an electroactive monomer and then directly deposited onto ITO/glass surface via electrochemical polymerization process. The observed electronic interaction only at the excited state due to the presence of phenylene spacer between SNS-donor and PDI-acceptor moiety leads to efficient fluorescence quenching. This charge separation behavior was also proved by theoretical DFT calculations. Thin films of the polymer electropolymerized onto transparent electrode exhibited ambipolar multi-electrochromic behavior including purple, violet-red-khaki-blue colors in both anodic and cathodic regime only between -1.2 and 1.0 V. We further demonstrated that this polymer film has a high contrast ratio (Delta T = 45% at 900 nm), a faster response (0.5 s), high coloration efficiency (254 cm(2) C-1) and retained its performance by 92% even after 5000 cycles. (C) 2014 Elsevier Ltd. All rights reserved.Öğe A new conducting polymer of 2,5-bis(2-thienyl)-1H-(pyrrole) (SNS) containing carbazole subunit: Electrochemical, optical and electrochromic properties(Elsevier Science Sa, 2009) Koyuncu, Sermet; Zafer, Ceylan; Sefer, Emre; Koyuncu, Fatma Baycan; Demic, Serafettin; Kaya, Ismet; Ozdemir, Eyup; Icli, SiddikWe report here the synthesis of a new electroactive monomer 3,6-di-tert-butyl-[4-(2,5-di-2-thienyl-1H-pyrrol-1-yl)phenyl]-9H-carbazole in five steps and polymerization of this monomer by two different procceses: Kumada Coupling and electro-oxidative. The product obtained by chemical polymerization exhibits a high thermal stability and narrow molecular weight distribution. While, in the UV-vis absorption spectrum of monomer the absorption peaks appear at 338 nm, the chemically synthesized polymer absorbs at 428 nm with 90 nm red shift. Cyclic voltammogram of monomer shows two separate oxidation processes which reflect the first oxidation at +0.84 V and a second one at +1.43 V. When the polymeric film prepared by electrochemical process was subjected to a repeated cyclic scan between -0.2V and +1.0V, it switches among three different colors (orange, green and blue). The oxidation and reduction response times were calculated as 2.0 s for this polymer film and exhibits high redox stability. The results anticipate that this kind of polymers can be used for designing electrochromics based on the use of one molecule for the generation of three basic colors (RGB). (C) 2009 Elsevier B.V. All rights reserved.Öğe A new conducting polymer of 2,5-bis(2-thienyl)-1H-(pyrrole) (SNS) containing carbazole subunit: Electrochemical, optical and electrochromic properties(Elsevier Science Sa, 2009) Koyuncu, Sermet; Zafer, Ceylan; Sefer, Emre; Koyuncu, Fatma Baycan; Demic, Serafettin; Kaya, Ismet; Ozdemir, Eyup; Icli, SiddikWe report here the synthesis of a new electroactive monomer 3,6-di-tert-butyl-[4-(2,5-di-2-thienyl-1H-pyrrol-1-yl)phenyl]-9H-carbazole in five steps and polymerization of this monomer by two different procceses: Kumada Coupling and electro-oxidative. The product obtained by chemical polymerization exhibits a high thermal stability and narrow molecular weight distribution. While, in the UV-vis absorption spectrum of monomer the absorption peaks appear at 338 nm, the chemically synthesized polymer absorbs at 428 nm with 90 nm red shift. Cyclic voltammogram of monomer shows two separate oxidation processes which reflect the first oxidation at +0.84 V and a second one at +1.43 V. When the polymeric film prepared by electrochemical process was subjected to a repeated cyclic scan between -0.2V and +1.0V, it switches among three different colors (orange, green and blue). The oxidation and reduction response times were calculated as 2.0 s for this polymer film and exhibits high redox stability. The results anticipate that this kind of polymers can be used for designing electrochromics based on the use of one molecule for the generation of three basic colors (RGB). (C) 2009 Elsevier B.V. All rights reserved.Öğe A New Donor-Acceptor Double-Cable Carbazole Polymer with Perylene Bisimide Pendant Group: Synthesis, Electrochemical, and Photovoltaic Properties(John Wiley & Sons Inc, 2009) Koyuncu, Sermet; Zafer, Ceylan; Koyuncu, Fatma Baycan; Aydin, Banu; Can, Mustafa; Sefer, Emre; Ozdemir, Eyup; Icli, SiddikWe report here electrochemical synthesis of novel soluble donor-acceptor (D-A) polymer with suitably functionalized perylenetetracarboxylic diimide dye derivative covalently linked to carbazole moiety (Cbz-PDI). The band gap, E, was measured using UV-Vis spectroscopy and compared with that obtained by cyclic voltammetry (CV). Efficient intramolecular electron transfer from carbazole-donor to perynediimide-acceptor leads to remarkable fluorescence quenching of the perylene core. Furthermore, spectroelectrochemical property and surface morphology of the polymer film were investigated. Characteristic monoanion and dianion radical bands on the UV-Vis absorption spectra attributed to the electrochemical reduction of the neutral polymer were observed. During the reduction process, red color of the film turned into blue and violet, respectively. Finally, the photovoltaic performance of the D-A double-cable polymer was checked and nearly 0.1% electrical conversion efficiency is obtained under simulated AM 1.5 solar light with 100 mW/cm(2) radiation power. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6280-6291, 2009Öğe A New Donor-Acceptor Double-Cable Carbazole Polymer with Perylene Bisimide Pendant Group: Synthesis, Electrochemical, and Photovoltaic Properties(John Wiley & Sons Inc, 2009) Koyuncu, Sermet; Zafer, Ceylan; Koyuncu, Fatma Baycan; Aydin, Banu; Can, Mustafa; Sefer, Emre; Ozdemir, Eyup; Icli, SiddikWe report here electrochemical synthesis of novel soluble donor-acceptor (D-A) polymer with suitably functionalized perylenetetracarboxylic diimide dye derivative covalently linked to carbazole moiety (Cbz-PDI). The band gap, E, was measured using UV-Vis spectroscopy and compared with that obtained by cyclic voltammetry (CV). Efficient intramolecular electron transfer from carbazole-donor to perynediimide-acceptor leads to remarkable fluorescence quenching of the perylene core. Furthermore, spectroelectrochemical property and surface morphology of the polymer film were investigated. Characteristic monoanion and dianion radical bands on the UV-Vis absorption spectra attributed to the electrochemical reduction of the neutral polymer were observed. During the reduction process, red color of the film turned into blue and violet, respectively. Finally, the photovoltaic performance of the D-A double-cable polymer was checked and nearly 0.1% electrical conversion efficiency is obtained under simulated AM 1.5 solar light with 100 mW/cm(2) radiation power. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6280-6291, 2009Öğe A new processable donor-acceptor polymer displaying neutral state yellow electrochromism(Elsevier Sci Ltd, 2013) Oguzhan, Eda; Bilgili, Hakan; Koyuncu, Fatma Baycan; Ozdemir, Eyup; Koyuncu, SermetWe report here the synthesis of a new solution processable neutral state yellow polymeric electrochromic material containing 2,5-bis-dithienyl-1H-pyrrole (SNS)-donor and 1,8 naphthalimide-acceptor (SNS-NI) as a subunit. The electrochemical and optical properties were investigated via cyclic voltammetry (CV), UV Vis absorption and fluorescence emission measurements, respectively. Besides, electrochromic performance of poly(SNS NI) has been compared to the both the film preparation method and poly(1-phenyl-2,5-dithiophen-2-ylpyrrole) [poly(SNS-P)] as a standard polymer. In the poly(SNS-NI), yellow color of the polymer film at neutral state converted to green and then dark blue upon the polymer film fully oxidized in the positive regime. SNS NI polymer film prepared via spin casting process exhibits a high contrast ratio in the near-IR region (Delta T% = 56% at 890 nm), a response time of about 1 s, high coloration efficiency (299 cm(2) C-1) and retained its performance by 98.6% even after 5000 cycles. Finally, the results clearly indicate that both electronic nature of the molecule and film preparation method have a major impact on electrochromic performance of these polymers. Crown Copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.Öğe A Novel High-Contrast Ratio Electrochromic Material from Spiro[cyclododecane-1,9 '-fluorene]bicarbazole(Wiley-Blackwell, 2011) Usluer, Ozlem; Koyuncu, Sermet; Demic, Serafettin; Janssen, Rene A. J.A novel electroactive spirocyclododecylfluorene monomer named 2,7-bis(carbazol-9-yl)-9,9'-spiro[cyclododecane- 1,9'-fluorene] (SFC) was synthesized and electrochemically polymerized to give a very stable multi-electrochromic polymer (poly-SFC). Two separate oxidation processes were observed for both SFC monomer and poly-SFC that carries two carbazole units. The polymeric film of poly-SFC was coated onto ITO/glass surface, and it shows different colors (transparent, yellowish green, green, and dark green) upon stepwise oxidations. An electrochromic device based on poly-SFC was assembled in the sandwich cell configuration of ITO/poly-SFC// gel electrolyte//PEDOT/ITO. Poly-SFC exhibits 90% of transparency at neutral state and a high contrast ratio (Delta T = 58% at 800 nm). This device constructed from it represents a response time of about 1 s, high coloration efficiency (1377 cm(2) C-1) and retained its performance by 96.4% even after 1000 cycles. Exhibiting high transparency at neutral state, reversible redox behavior, resistance to overoxidation, and especially high contrast ratio at near IR region can make poly-SFC be useful and promising candidate for electrochromic applications despite having a relatively slow response time. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 333-341, 2011Öğe Push-pull type material having spirobifluorene as pi-spacer for dye sensitized solar cells(Pergamon-Elsevier Science Ltd, 2016) Can, Mustafa; Bilgili, Hakan; Demirak, Kadir; Gultekin, Burak; Koyuncu, Sermet; Kus, Mahmut; Zafer, Ceylan; Demic, Serafettin; Icli, SiddikTwo organic dyes for dye-sensitized solar cells (DSSC) based on spirobifluorene were synthesized and characterized. Electrochemical, spectroscopic and photovoltaic properties of the dyes have been investigated. Hexyloxy substituted triarylamine was used as electron donating moiety in the molecule while spirobifluorene and cyanoacrylic acid were used as pi-bridge and acceptor groups, respectively. MK162-sensitized solar cells exhibited a short-circuit current (I-SC) of 4,92 mA cm(-2), an open-circuit voltage (V-OC) of 520 mV and a fill factor (FF) of 0.59, resulting an overall power conversion efficiency of 1,52 where the reference cell, Z907 was yielded an overall conversion efficiency of 4.08% efficiency with 620 mV of V-OC and 14.51 mA cm(-2) of Isc under standard AM 1.5 illumination. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Quantification of the Effects of Recombination and Injection in the Performance of Dye-Sensitized Solar Cells Based on N-Substituted Carbazole Dyes(Amer Chemical Soc, 2010) Barea, Eva M.; Zafer, Ceylan; Gultekin, Burak; Aydin, Banu; Koyuncu, Sermet; Icli, Siddik; Fabregat Santiago, Francisco; Bisquert, JuanTwo new sensitizers for dye sensitized solar cells have been designed consisting of thiophene units asymmetrically functionalized by N-aryl carbazole. The di(tert-butyl) carbazole moieties acts as an electron donor group, the thiophene chain as a bridge group, and the cyanoacrylic acid as an anchoring and electron acceptor group. An increase of the conjugation length produces two main effects: first, it leads to a red-shift of the optical absorption of the dyes, resulting in an improved overlap of the absorption with the solar spectrum. Second, the oxidation potential decreases. The photovoltaic performance of this set of dyes as sensitizers in mesoporous TiO2 solar cells was investigated using electrolytes containing the iodide/triiodide redox couple. The dye with the best absorption characteristics showed the highest photocurrent but lower open circuit voltage due to more losses by recombination. A trend between structure (molecule dyes size) and recombination is demostrated using an analysis procedure based on beta-recombination model that combines impedance spectroscopy and density current-voltage data.Öğe Solution processable neutral state colourless electrochromic devices: effect of the layer thickness on the electrochromic performance(Royal Soc Chemistry, 2016) Tahtali, Gurhan; Has, Zeynep; Doyranli, Ceylan; Varlikli, Canan; Koyuncu, SermetIn this study, a neutral state colourless electrochromic device fabricated through a solution process is introduced. The device contains indium doped transparent oxide coated glass as the transparent conductive electrode, poly(N-(2-ethylhexyl) carbazol-3,6-diyl) (PCbz) as the anodically colouring material, poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) as the ion storage layer and a lithium perchlorate based conducting gel electrolyte. A maximum optical contrast (Delta T%) of 58% at 800 nm is achieved by optimizing the film thickness of both the organic layers. The device that has layers of 220 nm PCbz and 120 nm PEDOT: PSS thickness revealed a high coloration efficiency (1246 cm(2) C-1) and colouring and bleaching response times of 5.6 s and 2.3 s, respectively.
