scholarly journals Approaching the Spin-Statistical Limit in Visible-to-UV Photon Upconversion

2021 ◽  
Author(s):  
Axel Olesund ◽  
Jessica Johnsson ◽  
Fredrik Edhborg ◽  
Shima Ghasemi ◽  
Kasper Moth-Poulsen ◽  
...  
Keyword(s):  
Quantum Yield ◽  
Transient Absorption ◽  
High Energy ◽  
Delayed Fluorescence ◽  
Photochemical Reactions ◽  
Quantum Yields ◽  
Great Promise ◽  
Time Resolved ◽  
Statistical Limit ◽  
Triplet Triplet Annihilation

Triplet-triplet annihilation photon upconversion (TTA-UC) is a process in which triplet excitons combine to form emissive singlets, and holds great promise to improve the spectral match in solar energy and biological applications. While high TTA-UC quantum yields has been reported for e.g., red-to-green TTA-UC systems there are only a few examples of visible-to-UV transformations in which the quantum yield reaches 10%. In this study we investigate the performance of six annihilators when paired with the sensitizer 2,3,5,6-tetra(9H-carbazol-9-yl)benzonitrile (4CzBN), a purely organic compound that exhibits thermally activated delayed fluorescence (TADF). We report a record-setting TTA-UC quantum yield of 16.8% (out of a 50% maximum) for 1,4-bis((triisopropylsilyl)ethynyl)naphthalene (TIPS-Naph), demonstrating the first example of a visible-to-UV TTA-UC system approaching the classical spin-statistical limit of 20%. Three other annihilators, of which 2,5-diphenylfuran (PPF) has never been used for TTA-UC previously, also showed impressive performances with TTA-UC quantum yields above 12%. In addition, a new method to determine the rate constant of triplet-triplet annihilation is proposed in which only time-resolved emission measurements are needed, circumventing the need for more challenging transient absorption measurements. The results reported herein represent an important step towards highly efficient visible-to-UV TTA-UC systems which hold great potential for driving high-energy photochemical reactions.

Der Einfluß der Bandbreite des Anregungslichtes bei der Bestimmung von Quantenausbeuten photochemischer Reaktionen / The Influence of the Bandwidth of the Exciting Light in Determining the Quantum Yields of Photochemical Reactions

1979 ◽  
Vol 34 (11) ◽  
pp. 1344-1351
Author(s):  
R. Schöneich ◽  
J. Bendig ◽  
D. Kreysig
Keyword(s):  
Quantum Yield ◽  
Radiation Intensity ◽  
Photochemical Reactions ◽  
Wave Number ◽  
Quantum Yields ◽  
Exciting Light ◽  
Considerable Influence ◽  
Interference Filters

Monochromatic excitation is one of the experimental requirements for determining quantum yields of photochemical reactions. It can, however, be strictly satisfied only in certain conditions. The photoisomerization of E,E-1,4-diphenylbutadiene-(1,3) is taken as an example for studying the effect of the bandwidth of the exciting light by using interference filters. The bandwidth is shown to have a considerable influence on the experimentally determined value of the partial quantum yield. Identical results are obtained when making allowance for the wave number dependence on radiation intensity and the absorption of the reactant compounds

Time-Resolved Pulsed FT-IR Emission Studies of Photochemical Reactions

1993 ◽  
Vol 47 (9) ◽  
pp. 1438-1445 ◽  
Author(s):  
D. E. Heard ◽  
R. A. Brownsword ◽  
D. G. Weston ◽  
G. Hancock
Keyword(s):  
Plasma Etching ◽  
Infrared Emission ◽  
Photochemical Reactions ◽  
Quantum Yields ◽  
Time Resolved ◽  
Ion Plasma ◽  
Ft Ir ◽  
Ir Emission ◽  
Product Species ◽  
Emission Studies

A time-resolved Fourier transform emission spectrometer, operating in the stop-scan mode, is demonstrated as an inexpensive and versatile instrument for observation of infrared vibrational chemiluminescence. The entire evolution of an emission spectrum is obtained from a single scan of the interferometer, with a spectral and temporal resolution of 2 cm−1 and 10 ns, respectively. Results are presented for a number of radical-radical reactions studied by this technique, where emission from highly excited CO, HF, CO2, and N2O is observed. Measurements include nascent vibrational distributions, quantum yields for branching into different product channels, and bimolecular rate constants for the production and vibrational relaxation of product species. Experiments at low total pressure enable nascent vibrational and rotational distributions to be found for the HF fragment of the CO2 laser photolysis of 1,1-chlorofluoroethylene. In addition, time-resolved spectra of HF, CO, CO2, CF4, and CHF3 are demonstrated for infrared emission observed from a reactive ion plasma etching chamber.

Environmental Effects on the Relationship Between the Quantum Yields of Carbon Assimilation and in vivo PsII Electron Transport in Maize

1991 ◽  
Vol 18 (3) ◽  
pp. 267 ◽  
Author(s):  
JP Krall ◽  
GE Edwards
Keyword(s):  
Electron Transport ◽  
Energy Dissipation ◽  
Quantum Yield ◽  
High Energy ◽  
Co2 Assimilation ◽  
Quantum Yields ◽  
Photon Flux ◽  
Ps Ii ◽  
C4 Species ◽  
The Relationship

The partitioning of light energy absorbed by photosystem (PS) II in the C4 species maize was investigated under various photosynthetic photon flux densities (PPFD), temperatures, and intercellular CO2 concentrations. The relationship between the quantum yield of PSII electron transport (�e) and the quantum yield of CO2 assimilation (ΦCO2) was generally found to be linear, with similar slopes. This indicates that PSII electron transport is tightly coupled to CO2 assimilation such that measurements of �e may be used to estimate photosynthetic rates in maize. Coefficients of quenching of PSII chlorophyll fluorescence indicated that, under excessive PPFD or when CO2 assimilation was decreased due to suboptimal or supraoptimal temperature or low Ci, the energy in excess of that needed to drive the reduced rate of PSII electron transport was dissipated via a mechanism known to be correlated to the trans-thylakoid proton gradient (high energy quenching, qE) and a mechanism believed to arise in the PSII antenna chlorophyll (qN(slow)). At suboptimal temperature the energy dissipation was principally at the antenna level and qE was low, while at supraoptimal temperature the reverse was true. The results are discussed relative to coupling of PSII activity to CO2 fixation and mechanisms of energy dissipation in this C4 species.

Zur Anwendimg vpm Extinktionsdiagrammen bei der kinetischen Analyse von Photoreaktionen / Kinetic Analysis of Photochemical Reactions Using Extinction Diagrams

1972 ◽  
Vol 27 (11) ◽  
pp. 1354-1359 ◽  
Author(s):  
Heinz Mauser ◽  
Volker Starrock ◽  
Hans-Joachim Niemann
Keyword(s):  
Quantum Yield ◽  
Kinetic Analysis ◽  
Rate Constant ◽  
Extinction Coefficient ◽  
Photochemical Reactions ◽  
Experimental Results ◽  
Quantum Yields ◽  
Reaction Step ◽  
Consecutive Reaction ◽  
Consecutive Reactions

The reaction of anthraquinone in alkaline methanol irradiated with 313 nm light is followed spectrophotometrically. The experimental results point to an irreversible consecutive reaction A → B → C. Since the concentration and extinction coefficient of the intermediate are unknown, the partial quantum yield cannot be calculated. A new method is described for calculation of the concentration of the unknown intermediate using the extinction diagram. It is suitable for consecutive reactions, if the rate constant of the first reaction-step is very great as compared with that of the second. Now the partial quantum yields of the two reaction-steps can be calculated.

scholarly journals Photochemical α-Cleavage Reaction of 3’,5’-Dimethoxybenzoin: A Combined Time-Resolved Spectroscopy and Computational Chemistry Study

Molecules ◽  
2020 ◽  
Vol 25 (15) ◽  
pp. 3548
Author(s):  
Yuanchun Li ◽  
Xiting Zhang ◽  
Zhiping Yan ◽  
Lili Du ◽  
Wenjian Tang ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Quantum Yield ◽  
Dft Calculations ◽  
Density Functional ◽  
Transient Absorption ◽  
Type I ◽  
Functional Theory ◽  
Time Resolved ◽  
Norrish Type ◽  
Intramolecular Hydrogen

Benzoin is one of the most commonly used photoinitiators to induce free radical polymerization. Here, improved benzoin properties could be accomplished by the introduction of two methoxy substituents, leading to the formation of 3’,5’-dimethoxybenzoin (DMB) which has a higher photo-cleavage quantum yield (0.54) than benzoin (0.35). To elucidate the underlying reaction mechanisms of DMB and obtain direct information of the transient species involved, femtosecond transient absorption (fs-TA) and nanosecond transient absorption (ns-TA) spectroscopic experiments in conjunction with density functional theory/time-dependent density functional theory (DFT/TD-DFT) calculations were performed. It was found that the photo-induced α-cleavage (Norrish Type I reaction) of DMB occurred from the nπ* triplet state after a rapid intersystem crossing (ISC) process (7.6 ps), leading to the generation of phenyl radicals on the picosecond time scale. Compared with Benzoin, DMB possesses two methoxy groups which are able to stabilize the alcohol radical and thus result in a stronger driving force for cleavage and a higher quantum yield of photodissociation. Two stable conformations (cis-DMB and trans-DMB) at ground state were found via DFT calculations. The influence of the intramolecular hydrogen bond on the α-cleavage of DMB was elaborated.

scholarly journals Photophysical relaxation mechanism of excited phtalimide compounds

2019 ◽  
Vol 58 (4) ◽  
Author(s):  
Ignas Čiplys ◽  
Ryoji Orita ◽  
Shinji Ando ◽  
Vidmantas Gulbinas
Keyword(s):  
Transient Absorption ◽  
Relaxation Mechanism ◽  
Quantum Yields ◽  
Solvent Mixtures ◽  
Electronic Components ◽  
Time Resolved Fluorescence ◽  
Model Compounds ◽  
Time Resolved ◽  
Fluorescent Materials ◽  
Intramolecular Rotation

Fluorescent polymers are one of the most desired materials for making novel flexible electronic components or spectral converters. Favourable properties of polyimides (PIs) make them a potentially attractive class of polymers but, unfortunately, they generally show a very weak fluorescence. As a result, there has been a large amount of work directed towards finding the reasons behind the lack of fluorescence of PIs and making their new fluorescent variants. Amine-substituted phtalimides are heavily used as model compounds for fluorescent PIs. In this work we have examined the photophysical relaxation mechanism of such two phtalimides (3Pi and 3Pyr) that were previously discovered to have low quantum yields of fluorescence. Our aim was to find the reason behind this lack of fluorescence and to suggest ways to make these properties more attractive. We have investigated the photophysics of phtalimides by time resolved fluorescence and ultrafast transient absorption techniques in solvent mixtures of different viscosities. Our results demonstrate that intramolecular rotation is a crucial process that opens up an alternative relaxation pathway to fluorescence in phtalimides, which has to be suppressed for designing more fluorescent materials.

scholarly journals Triplet–triplet annihilation in highly efficient fluorescent organic light-emitting diodes: current state and future outlook

2015 ◽  
Vol 373 (2044) ◽  
pp. 20140321 ◽  
Author(s):  
Denis Y. Kondakov
Keyword(s):  
Light Emitting Diodes ◽  
Practical Importance ◽  
Delayed Fluorescence ◽  
Organic Light Emitting Diodes ◽  
Light Emitting ◽  
Highly Efficient ◽  
Organic Light ◽  
Statistical Limit ◽  
Special Cases ◽  
Triplet Triplet Annihilation

Studies of delayed electroluminescence in highly efficient fluorescent organic light-emitting diodes (OLEDs) of many dissimilar architectures indicate that the triplet–triplet annihilation (TTA) significantly increases yield of excited singlet states—emitting molecules in this type of device thereby contributes substantially to their efficiency. Towards the end of the 2000s, the essential role of TTA in realizing highly efficient fluorescent devices was widely recognized. Analysis of a diverse set of fluorescent OLEDs shows that high efficiencies are often cor-related to TTA extents. It is therefore likely that it is the long-term empirical optimization of OLED efficiencies that has resulted in fortuitous emergence of TTA as a large and ubiquitous contributor to efficiency. TTA contributions as high as 20–30% are common in the state-of-the-art OLEDs, and even become dominant in special cases, where TTA is shown to substantially exceed the spin-statistical limit. The fundamental features of OLED efficiency enhancement via TTA—molecular structure-dependent contributions, current density-dependent intensities in practical devices and frequently observed antagonistic relationships between TTA extent and OLED lifetime—came to be understood over the course of the next few years. More recently, however, there was much less reported progress with respect to all-important quantitative details of the TTA mechanism. It should be emphasized that, to this day and despite the decades of work on improving blue phosphorescent OLEDs as well as the recent advent of thermally activated delayed fluorescence OLEDs, the majority of practical blue OLEDs still rely on TTA. Considering such practical importance of fluorescent blue OLEDs, the design of blue OLED-compatible materials capable of substantially exceeding the spin-statistical limit in TTA, elimination of the antagonistic relationship between TTA-related efficiency gains and lifetime losses, and designing devices with an extended range of current densities producing near-maximum TTA electroluminescence are the areas where future improvements would be most beneficial.

Isomerization enhanced quantum yield of dibenzo[a,c]phenazine-based thermally activated delayed fluorescence emitters for highly efficient orange OLEDs

2020 ◽  
Vol 8 (28) ◽  
pp. 9639-9645
Author(s):  
Changjiang Zhou ◽  
Wen-Cheng Chen ◽  
He Liu ◽  
Xiaosong Cao ◽  
Nengquan Li ◽  
...  
Keyword(s):  
Quantum Yield ◽  
Delayed Fluorescence ◽  
Quantum Yields ◽  
Thermally Activated Delayed Fluorescence ◽  
Thermally Activated ◽  
Highly Efficient

Highly efficient orange/red OLED emitters are obtained with isomerization enhanced quantum yields.

Low-Power Triplet-Triplet Annihilation Upconversion with a New Anthracene Derivatives

2016 ◽  
Vol 852 ◽  
pp. 1265-1270
Author(s):  
Sai Jiang Zhu ◽  
Chang Qing Ye ◽  
Yan Fu ◽  
Zuo Qing Liang ◽  
Xiao Mei Wang
Keyword(s):  
Quantum Yield ◽  
Low Power ◽  
Power Density ◽  
High Efficiency ◽  
Excitation Power ◽  
Quantum Yields ◽  
Excitation Power Density ◽  
High Quantum ◽  
Anthracene Derivatives ◽  
Triplet Triplet Annihilation

Two new anthracene derivatives were synthesized as emitter for low power triplet-triplet annihilation upconversion. Compared with anthracene, the emitter exhibits high quantum yields up to 85%. Pd (II) tetraphenylporphyrin which was selected as the sensitizer with the existence of BBA in DMF, We find a pretty high efficiency (Φuc=21.9%) of the upconversion fluorescence at 532nm with a low excitation power density of 0.5w/cm2.With the comparison of Anthracene, BBA and BTPA systems, quantum yield of the emitter is very important to the improving of the efficiency of upconversion.

PDT-related photophysical properties of conformationally distorted palladium(II) porphyrins

2001 ◽  
Vol 05 (12) ◽  
pp. 853-860 ◽  
Author(s):  
A. WIEHE ◽  
H. STOLLBERG ◽  
S. RUNGE ◽  
A. PAUL ◽  
M. O. SENGE ◽  
...  
Keyword(s):  
Quantum Yield ◽  
Molecular Oxygen ◽  
Photophysical Properties ◽  
Bathochromic Shift ◽  
Luminescence Spectroscopy ◽  
Quantum Yields ◽  
Triplet States ◽  
Singlet Molecular Oxygen ◽  
Time Resolved ◽  
Phosphorescence Quantum Yield

The photodynamic therapy (PDT) related photophysical properties of five palladium(II) porphyrins with increasing steric demand of the meso-substituents were investigated by steady state and time-resolved absorption and luminescence spectroscopy. The steric strain of the meso-substituents is reflected in a bathochromic shift of the B-band in the absorption spectra. In contrast to free-base porphyrins, the palladium(II) complexes exhibit only a very weak fluorescence with Φ Fl ~ 10-4. Instead, the corresponding triplet states of the porphyrins are formed via inter system crossing (ISC) with a quantum yield ΦISC of nearly unity. A phosphorescence quantum yield ΦISC of 10-4 was determined assuming dynamic quenching. The triplet state of all compounds is efficiently quenched by molecular oxygen, generating singlet molecular oxygen with a quantum yield of ΦΔ ~ 0.85. The various substitution patterns exerted no significant influence on the ISC rates or singlet oxygen quantum yields. Significant differences, on the other hand, were observed with respect to the triplet lifetimes, with a tendency of longer lifetimes for the porphyrins with sterically more demanding substituents (in air-saturated solution). All porphyrins were successfully incorporated into liposomes. The phototoxic activity of three compounds was investigated in cell suspensions. The use of the new porphyrinato-palladium(II) in PDT applications is discussed.

Sign in / Sign up

Export Citation Format

Share Document