Triplet Absorption Research Articles

Probing mechanism of Rhodamine B decolorization under homogeneous conditions via pH-controlled photocatalysis with anionic porphyrin

Porphyrins are acknowledged for their efficacy as photosensitizers and show potential for the treatment of water contaminated with diverse dyes. This research emphasizes the use of meso-tetra(4-sulfonatophenyl)porphyrin (TPPS) as a photosensitizer for purifying water contaminated with rhodamine B. Investigations were conducted under homogeneous conditions using visible light irradiation, revealing the efficacy of the porphyrin in the decolorization of rhodamine B strongly depends on pH of the solution. This study demonstrated that within 120 min, the decolorization process rapidly removed about 95% of RhB at an initial pH of 3.0, while at pH 6.0, the removal rate was significantly lower, at only 12%. An extensive photophysical study of the TPPS was carried out at pH 6.0 and pH 3.0 including absorption and fluorescence spectra, fluorescence quantum yields, triplet absorption spectra, triplet lifetimes, triplet and singlet oxygen quantum yields in order to explain difference in the efficiency of RhB discoloration. A thorough investigation into mechanism revealed that neither reactive oxygen species nor singlet oxygen played a role in RhB decolorization within this system. Instead, the predominant route was found to be the electron transfer from photoexcited TPPS to RhB, followed by proton transfer at pH 3.0, leading to the generation of a colorless leuco form.

Macrocyclic porphyrin photocatalysts without metal chelation: A novel pathway for complete degradation of tough halophenols with longwave visible LED light source

Halophenols are toxic and persistent pollutants in water environments which poses harm to various organisms. Due to their high stability and long residence time, ultraviolet radiation, heavy metals and oxidizing agents have been largely adopted on treating these compounds. However, these treatment methods could pose toxicity or hazardous risks to the marine environment and plant operators. In this study, a water-soluble porphyrin photocatalyst was synthesized and introduced for halophenol treatment using UV-free LED white light. The porphyrin catalyst is a macrocyclic ring consisting of pyrroles linked with methine bridges, the highly conjugated ring provided the superior functionality of visible light absorption. Surprisingly, over 99 % degradation of halophenols and over 90 % dehalogenation have been achieved without metal chelation, even higher than those of transition metal porphyrins with inclusion of Fe3+, Zn2+, Cu2+, Co2+, Ni2+, and Mn2+. Ring-opening reactions were confirmed with the formation of carboxylic acids; dicarboxylic acids like acrylic acid, and malonic acid; while fumaric acid was the main product. Total organic carbon results indicated no CO2 produced during the reaction. Triplet absorbance and scavenger studies also indicated that singlet oxygen and conduction band electrons are the main radical species for halophenol degradation. The 100-fold singlet emission quenching over triplet absorption quenching indicated that the excited electrons tend to be transferred via singlet state. This concept brings along new approaches detoxifying halophenol-related wastewater without UV, metals and other additives, which is more environmentally-friendly and sheds light to the conversion of toxic materials into useful chemical precursors.

Tetra‐Donor Pyrazine Based Thermally Activated Delayed Fluorescence Emitters for Electroluminescence and Amplified Spontaneous Emission

AbstractThermally activated delayed fluorescence (TADF) materials are expected to address triplet‐related losses in electrically driven organic lasers, as the electrically generated triplets in the materials can be converted to radiative singlets through reverse intersystem crossing (RISC). This offers a way to bypass triplet absorption and annihilation in organic semiconductor lasers (OSLs). In this work, two versatile TADF emitters 4tCzPz and 4αCbPz for application in organic light‐emitting diodes (OLEDs) and OSLs are presented. Both emitters possess moderately high singlet‐triplet energy gap, ΔEST (≈0.30 eV) and show high photoluminescence quantum yields, ΦPL, in solution and solid‐state and prominent stimulated emission features in solution. Films of 4tCzPz and 4αCbPz doped in mCBP show an amplified spontaneous emission (ASE) threshold of 41.0 and 44.9 µJ/cm2, respectively. The OLEDs with 4tCzPz and 4αCbPz emit with peak wavelengths of 492 and 475 nm, respectively, and show corresponding maximum external quantum efficiencies, EQEmax, of 24.6 and 21.3%. The research shows that D‐A TADF materials hold significant potential not only as emitters for OLEDs but also in OSLs.

Post-macrocyclization strategy to octaphenoxy-substituted zinc pyrazinoporphyrazine, its photochemical and electrochemical properties

An efficient post-macrocyclization strategy to new octaphenoxy-substituted zinc pyrazinoporphyrazine has been developed. This approach allows avoiding the template synthesis of the target compound from the phenoxy-substituted dinitrile, during which oligomerization and phenol release occur. The possibility of obtaining the initial octachloropyrazinoporphyrazine using template synthesis activated thermally and using microwave irradiation has been shown. Octaphenoxy-substituted zinc pyrazinoporphyrazine demonstrates short but intense triplet signals in triplet absorption spectrum and substantial singlet oxygen quantum yield (ΦΔ = 0.34). The fluorescent properties and fluorescence decay kinetics of target porphyrazines were studied. In contrast to the initial poorly soluble chlorinated complex, cyclic voltammetric measurements show both reduction and oxidation processes. Two waves of reduction and one wave of oxidation were observed. The electron-donating nature of phenoxy groups compared to chlorine groups is shown.

Extremely Low Threshold Quasi‐CW Amplified Spontaneous Emission Achieving and Its Mechanism Study

AbstractThe development of lasing materials with weak pile‐up effect from triplet excitons, low lasing threshold, and long operational lifetime is much significant for truly continuous wave operation and electrically pumping organic lasers. However, most of organic gain media has been verified to have extreme quenching effect from triplet excitons due to its wide‐band distribution of triplet absorption spectrum. Here, it is found that the phenanthroimidazole derivatives as gain media have congenital advantages on handling triplet's issues. A very low amplified spontaneous emission (ASE) threshold of 0.56 µJ cm−2 and a long operational lifetime of 5.77 × 105 pump pulses in air atmosphere are well obtained. When increasing the pump repetition frequency from 20 Hz to 20 kHz, the operational lifetimes of the thin films have small reduction. Under a high pump repetition frequency of 200 kHz, which is quasi‐continuous wave operational regime, the PI2PhDPO thin film exhibits very low ASE threshold of 0.78 µJ cm−2 due to the tiny overlap between triplet absorption and ASE spectra.

A Rigid Multiple Resonance Thermally Activated Delayed Fluorescence Core Toward Stable Electroluminescence and Lasing.

The investigation of organic light-emitting diodes (OLEDs) and organic laser devices with thermally activated delayed fluorescence (TADF) molecules is emerging due to the potential of harnessing triplets. In this work, a boron/nitrogen multiple-resonance TADF polycyclic framework fusing carbazole units (CzBNPh) was proposed. CzBNPh exhibited a narrowband emission (<30 nm), a unity photoluminescence quantum yield, and a fast radiative rate. Consequently, CzBNPh demonstrated a low distributed feedback (DFB) lasing threshold of 0.68 μJ cm-2 . Furthermore, the stimulated emission zone of CzBNPh was effectively separated from its singlet and triplet absorption, thereby minimizing the singlet-triplet annihilation under long-pulsed excitation ranging from 20 μs to 2.5 ms. Significantly, the enhanced rigid molecular conformation, thermal stability, and photo-stability resulted in improved lasing and electroluminescence stability compared to that of 5,9-diphenyl-5,9-diaza-13b-boranaphtho[3,2,1-de]anthracene (DABNA)-core. These findings indicate the potential of CzBN-core as a promising framework for achieving long-pulsed wave and electrically-pumped lasing in the future.

A Rigid Multiple Resonance Thermally Activated Delayed Fluorescence Core Toward Stable Electroluminescence and Lasing

AbstractThe investigation of organic light‐emitting diodes (OLEDs) and organic laser devices with thermally activated delayed fluorescence (TADF) molecules is emerging due to the potential of harnessing triplets. In this work, a boron/nitrogen multiple‐resonance TADF polycyclic framework fusing carbazole units (CzBNPh) was proposed. CzBNPh exhibited a narrowband emission (&lt;30 nm), a unity photoluminescence quantum yield, and a fast radiative rate. Consequently, CzBNPh demonstrated a low distributed feedback (DFB) lasing threshold of 0.68 μJ cm−2. Furthermore, the stimulated emission zone of CzBNPh was effectively separated from its singlet and triplet absorption, thereby minimizing the singlet‐triplet annihilation under long‐pulsed excitation ranging from 20 μs to 2.5 ms. Significantly, the enhanced rigid molecular conformation, thermal stability, and photo‐stability resulted in improved lasing and electroluminescence stability compared to that of 5,9‐diphenyl‐5,9‐diaza‐13b‐boranaphtho[3,2,1‐de]anthracene (DABNA)‐core. These findings indicate the potential of CzBN‐core as a promising framework for achieving long‐pulsed wave and electrically‐pumped lasing in the future.

NIGHT: A compact, near-infrared, high-resolution spectrograph to survey helium in exoplanet systems

ABSTRACT Among highly irradiated exoplanets, some have been found to undergo significant hydrodynamic expansion traced by atmospheric escape. To better understand these processes in the context of planetary evolution, we propose NIGHT (the Near-Infrared Gatherer of Helium Transits). NIGHT is a high-resolution spectrograph dedicated to surveying and temporally monitoring He i triplet absorption at 1083 nm in stellar and planetary atmospheres. In this paper, we outline our scientific objectives, requirements, and cost-efficient design. Our simulations, based on previous detections and modelling using the current exoplanet population, determine our requirements and survey targets. With a spectral resolution of 70 000 on a 2-m telescope, NIGHT can accurately resolve the helium triplet and detect 1 per cent peak absorption in 118 known exoplanets in a single transit. Additionally, it can search for 3σ temporal variations of 0.4 per cent in 66 exoplanets in-between two transits. These are conservative estimates considering the ongoing detections of transiting planets amenable to atmospheric characterization. We find that instrumental stability at 40 m s−1, less stringent than for radial velocity monitoring, is sufficient for transmission spectroscopy in He i. As such, NIGHT can utilize mostly off-the-shelf components, ensuring cost-efficiency. A fibre-fed system allows for flexibility as a visitor instrument on a variety of telescopes, making it ideal for follow-up observations after JWST or ground-based detections. Over a few years of surveying, NIGHT could offer detailed insights into the mechanisms shaping the hot Neptune desert and close-in planet population by significantly expanding the statistical sample of planets with known evaporating atmospheres. First light is expected in 2024.

Mysterious non-detection of HeI (23S) transit absorption of GJ436b

Abstract Possible reasons for the non-detection of absorption in the metastable HeI(23S) line at transit observations of warm Neptune GJ436b, in spite of the well pronounced strong absorption features measured earlier in Lyα for this planet, are investigated. We perform numeric simulations of the escaping upper atmosphere of this planet and its HeI(23S) triplet absorption with a global 3D multi-fluid self-consistent hydrodynamic model. By fitting the model parameters to the lowest detection level of absorption measurements, we constrain an upper limit the He/H abundance three times smaller than the solar value. We demonstrate that neither the significant changes of the stellar wind related with possible stellar coronal mass ejections (CMEs), or possible variations in the stellar ionization radiation, nor the presence of heavy trace elements have crucial effect on the absorption at the 10 830 Å line of HeI(23S) triplet. The main reason of weak signature is that the region populated by the absorbing metastable helium is rather small (&amp;lt;3Rp), as well as the small size of the planet itself, in comparison to the host star. We show that the radiation pressure force acting on the HeI(23S) atoms spreads them along the line of sight and around the planet, thus further reducing peak absorption.

Remote sensing of desertification and study of temporal variability of aeolian deposits in parts of the Arabian Desert for sustainable development in an arid environment

Aeolian deposit in part of the Arabian Desert is mapped using ASTER data to understand desertification, land encroachment, and degradation, and to assess agricultural development in arid regions. In this study, the interpretation of emissive spectra of sand deposits showed the presence of triplet absorptions in emissivity between 8 and 9.50 μm and studied with ASTER spectral bands to map the deposits. The ASTER quartz index (QI) images used to study the Abu Samra region, Qatar from 2000 to 2021 showed significant changes in desertification and land degradation. Analysis of temporal variability of deposits between 2000 and 2021 using ASTER band 12 by Parallelepiped image classification showed a decreasing trend from 9.70% to 2.94% in their distributions due to erosion and transportation. The changes are studied using FCC images (R:1; G:2; B:3) and hill-shaded images of 2000 and 2021. The results are confirmed from FCC (R:14; G:12; B:11) and Google Earth satellite images which showed the occurrence of sabkhas in 1985 and their disappearance from 2015, and the presence of agriculture in 2000 and their absence from 2005. The changes in desertification, land degradation, and agricultural development are verified in the field and evidenced. The grain size analysis of samples by ASTM method showed aeolian deposits have very fine to very coarse (63–2000 μm) sand types with silts of <3%. The samples analyzed by XRD and SEM-EDX methods showed the occurrence of dolomite, calcite, quartz, feldspar, and gypsum minerals with high sphericity and sub-angular to well-rounded characters and suggested transportations of grains from long distances. The geochemical elements analyses of samples reflected the chemistry of carbonates, aluminosilicates, and evaporites minerals which could have been derived from the carbonate, shale and sandstone formations, and sabkhas that occurred in Qatar and the Arabian Peninsula.

Characterisation of the upper atmospheres of HAT-P-32 b, WASP-69 b, GJ 1214 b, and WASP-76 b through their He I triplet absorption

Characterisation of atmospheres undergoing photo-evaporation is key to understanding the formation, evolution, and diversity of planets. However, only a few upper atmospheres that experience this kind of hydrodynamic escape have been characterised. Our aim is to characterise the upper atmospheres of the hot Jupiters HAT-P-32b and WASP-69 b, the warm sub-Neptune GJ 1214 b, and the ultra-hot Jupiter WASP-76 b through high-resolution observations of their He I triplet absorption. In addition, we also reanalyse the warm Neptune GJ 3470 b and the hot Jupiter HD 189733 b. We used a spherically symmetric 1D hydrodynamic model coupled with a non-local thermodynamic equilibrium model for calculating the He I triplet distribution along the escaping outflow. Comparing synthetic absorption spectra with observations, we constrained the main parameters of the upper atmosphere of these planets and classify them according to their hydrodynamic regime. Our results show that HAT-P-32 b photo-evaporates at (130 ± 70) ×1011 g s−1 with a hot (12 400 ± 2900 K) upper atmosphere; WASP-69 b loses its atmosphere at (0.9 ± 0.5) ×1011 g s−1 and 5250 ± 750 K; and GJ 1214b, with a relatively cold outflow of 3750 ± 750 K, photo-evaporates at (1.3 ± 1.1) ×1011 g s−1. For WASP-76 b, its weak absorption prevents us from constraining its temperature and mass-loss rate significantly; we obtained ranges of 6000–17 000 K and 23.5 ± 21.5 ×1011 g s−1. Our reanalysis of GJ 3470 b yields colder temperatures, 3400 ± 350 K, but practically the same mass-loss rate as in our previous results. Our reanalysis of HD 189733 b yields a slightly higher mass-loss rate, (1.4 ± 0.5) × 1011 g s−1, and temperature, 12 700 ± 900 K compared to previous estimates. We also found that HAT-P-32 b, WASP-69 b, and WASP-76 b undergo hydrodynamic escape in the recombination-limited regime, and that GJ 1214 b is in the photon-limited regime. Our results support that photo-evaporated outflows tend to be very light, H/He ≳ 98/2. The dependences of the mass-loss rates and temperatures of the studied planets on the respective system parameters (X-ray and ultraviolet stellar flux, gravitational potential) are well explained by the current hydrodynamic escape models.

Photo-activated polymerization inhibition process in photoinitiator systems for high-throughput 3D nanoprinting

Abstract The systems for multiphoton 3D nanoprinting are rapidly increasing in print speed for larger throughput and scale, unfortunately without also improvement in resolution. Separately, the process of photoinhibition lithography has been demonstrated to enhance the resolution of multiphoton printing through the introduction of a secondary laser source. The photo-chemical dynamics and interactions for achieving photoinhibition in the various multiphoton photoinitiator systems are complex and still not well understood. Here, we examine the photoinhibition process of the common photoinitiator 7-diethylamino 3-thenoylcoumarin (DETC) with inhibition lasers near or at the multiphoton printing laser wavelength in typical low peak intensity, high repetition rate 3D nanoprinting processes. We demonstrate the clear inhibition of the polymerization process consistent with a triplet absorption deactivation mechanism for a DETC photoresist as well as show inhibition for several other photoresist systems. Additionally, we explore options to recover the photoinhibition process when printing with high intensity, low repetition rate lasers. Finally, we demonstrate photoinhibition in a projection multiphoton printing system. This investigation of photoinhibition lithography with common photoinitiators elucidates the possibility for photoinhibition occurring in many resist systems with typical high repetition rate multiphoton printing lasers as well as for high-speed projection multiphoton printing.

Unraveling the electronic origin of a special feature in the triplet-minus-singlet spectra of carotenoids in natural photosystems.

The influence of carotenoid triplet states on the Qy electronic transitions of chlorophylls has been observed in experiments on light-harvesting complexes over the past three decades, but the interpretation of the resulting spectral feature in the triplet minus singlet (T-S) absorption spectra of photosystems is still debated, as the physical-chemical explanation of this feature has been elusive. Here, we resolve this debate, by explaining the T-S spectra of pigment complexes over the Qy-band spectral region through a comparative study of chlorophyll-carotenoid model dyads and larger pigment complexes from the main light harvesting complex of higher plants (LHCII). This goal is achieved by combining state-of-the-art time-dependent density functional theory with analysis of the relationship between electronic properties and nuclear structure, and by comparison to the experiment. We find that the special signature in the T-S spectra of both model and natural photosystems is determined by singlet-like triplet excitations that can be described as effective singlet excitations on chlorophylls influenced by a stable electronic triplet on the carotenoid. The comparison with earlier experiments on different light-harvesting complexes confirms our theoretical interpretation of the T-S spectra in the Qy spectral region. Our results indicate an important role for the chlorophyll-carotenoid electronic coupling, which is also responsible for the fast triplet-triplet energy transfer, suggesting a fast trapping of the triplet into the relaxed carotenoid structure. The gained understanding of the interplay between the electronic and nuclear structures is potentially informative for future studies of the mechanism of photoprotection by carotenoids.

Specific Features in the Triplet–Triplet Absorption Spectra of Multi-Chromophoric Molecules: a Computational Study

Specific Features in the Triplet–Triplet Absorption Spectra of Multi-Chromophoric Molecules: a Computational Study

Detection of Paschenβabsorption in the atmosphere of KELT-9 b

Hydrogen and helium transmission signals trace the upper atmospheres of hot gas-giant exoplanets, where the incoming stellar extreme ultraviolet and X-ray fluxes are deposited. Further, for the hottest stars, the near-ultraviolet excitation of hydrogen in the Balmer continuum may play a dominant role in controlling the atmospheric temperature and driving photoevaporation. KELT-9 b is the archetypal example of such an environment as it is the hottest gas-giant exoplanet known to date (Teq ∼ 4500 K) and orbits an A0V-type star. Studies of the upper atmosphere and escaping gas of this ultra-hot Jupiter have targeted the absorption in the Balmer series of hydrogen (n1= 2 →n2&gt; 2). Unfortunately, the lowermost metastable helium state that causes the triplet absorption at 1083 Å is not sufficiently populated for detection. This is due to the low extreme-ultraviolet and X-ray fluxes from the host star, and to its high near-ultraviolet flux, which depopulates this metastable state. Here, we present evidence of hydrogen absorption in the Paschen series in the transmission spectrum of KELT-9 b observed with the high-resolution spectrograph CARMENES. Specifically, we focus on the strongest line covered by its near-infrared channel, Paβat 12 821.6 Å (n1= 3 →n2= 5). The observed absorption shows a contrast of (0.53−0.13+0.12)%, a blueshift of −14.8−3.2+3.5km s−1, and a full width at half maximum of 31.9−8.3+11.8km s−1. The observed blueshift in the absorption feature could be explained by day-to-night circulation within the gravitationally bound atmosphere or, alternatively, by Paβabsorption originating in a tail of escaping gas moving toward the observer as a result of extreme atmospheric evaporation. This detection opens a new window for investigating the atmospheres of ultra-hot Jupiters, providing additional constraints of their temperature structure, mass-loss rates, and dynamics for future modeling of their scorching atmospheres.

Modeling the Hα and He 10830 Transmission Spectrum of WASP-52b

Escaping atmosphere has been detected by the excess absorption of Lyα, Hα and He triplet (λ10830) lines. Simultaneously modeling the absorption of the Hα and He λ10830 lines can provide useful constraints about the exoplanetary atmosphere. In this paper, we use a hydrodynamic model combined with a non−local thermodynamic model and a new Monte Carlo simulation model to obtain the H(2) and He(23 S) populations. The Monte Carlo simulations of Lyα radiative transfer are performed with assumptions of a spherical stellar Lyα radiation and a spherical planetary atmosphere, for the first time, to calculate the Lyα mean intensity distribution inside the planetary atmosphere, necessary in estimating the H(2) population. We model the transmission spectra of the Hα and He λ10830 lines simultaneously in hot Jupiter WASP-52b. We find that models with many different H/He ratios can reproduce the Hα observations well if the host star has (1) a high X-ray and extreme-ultraviolet (XUV) flux (F XUV) and a relatively low X-ray fraction in XUV radiation (β m ) or (2) a low F XUV and a high β m . The simulations of the He λ10830 triplet suggest that a high H/He ratio (∼98/2) is required to fit the observation. The models that fit both lines well confine F XUV to be about 0.5 times the fiducial value and β m to have a value around 0.3. The models also suggest that hydrogen and helium originate from the escaping atmosphere, and the mass-loss rate is about 2.8 × 1011 g s−1.

Structural, optical, and dielectric properties of Co2+: Zn2SiO4 glass-ceramics for blue phosphor used in optoelectronic devices

For the first time, the author reported the fabrication and characterizations of Co2+ doped Zn2SiO4 (Co2+: Zn2SiO4) using the recycled waste white rice husk ash (WRHA) based on empirical formula (Co3O4)1.0[(ZnO)55.0(WRHA)45.0]99.0 and produced by using melt-quenching technique. The precursor glass was heat treated at 700 ℃ until 950 ℃. The X-ray diffraction (XRD) result of Co2+: Zn2SiO4 showed that β- Zn2SiO4 started to form at 750 ℃ and single phase of α-Zn2SiO4 remain stable at 950 ℃. The Fourier transform infrared spectroscopy (FTIR) confirmed the formation of Co2+: Zn2SiO4 by showing eight significant vibrational bands. One triplet absorption band occurred at around 450–700 nm attributed to 4A2 → 4T1 (4P) optical transition of Co2+ ions that gives blue color towards the Co2+: Zn2SiO4 sample. Emission spectroscopy of Co2+: Zn2SiO4 exhibit five different peaks corresponded to blue emission (~416 nm, ~441 nm, ~461 nm and ~481 nm) and green emission (~527 nm) under excitation at 325 nm. Such luminescence properties making Co2+: Zn2SiO4 as a potential phosphor material especially in providing blue emission supported by the excellent dielectric properties.

Inferred Measurements of the Zodiacal Light Absolute Intensity through Fraunhofer Absorption Line Spectroscopy with CIBER

Abstract Scattered sunlight from the interplanetary dust (IPD) cloud in our solar system presents a serious foreground challenge for spectrophotometric measurements of the extragalactic background light (EBL). In this work, we report on inferred measurements of the absolute intensity of the zodiacal light (ZL) using the novel technique of Fraunhofer line spectroscopy on the deepest 8542 Å line of the near-infrared Ca ii absorption triplet. The measurements are performed with the narrow band spectrometer (NBS) on board the Cosmic Infrared Background Experiment sounding rocket instrument. We use the NBS data to test the accuracy of two ZL models widely cited in the literature, the Kelsall and Wright models, which have been used in foreground removal analyses that produce high and low EBL results respectively. We find a mean reduced χ 2 = 3.5 for the Kelsall model and χ 2 = 2.0 for the Wright model. The best description of our data is provided by a simple modification to the Kelsall model, which includes a free ZL offset parameter. This adjusted model describes the data with a reduced χ 2 = 1.5 and yields an inferred offset amplitude of 46 ± 19 nW m−2 sr−1 extrapolated to 12500 Å. These measurements elude to the potential existence of a dust cloud component in the inner solar system whose intensity does not strongly modulate with the Earth’s motion around the Sun.

Molecular engineering of excited-state process for multicolor microcrystalline lasers

We realize multicolor microcrystalline lasers by engineering the excited-state overlap between the stimulated emission and triplet absorption based on the organic molecular design. These molecules possessing both high gain and potential high carrier transport behaviors can be attractive candidates for the electrically pumped organic laser.

Benzophenone based salicylaldimine and its boron complex as radical photoinitiator: A comparative study

Salicylaldimine derivatives are photochromatic dyes which could be easily synthesized from aromatic amine and salicylaldehyde. However, those compounds were rarely reported as photoinitiator. In this work, a salicylaldimine containing benzophenone moiety (BPH), and its boron complex (BPB) were synthesized and carried out as radical photoinitiator under 365/405 nm LED lamps. BPB was never synthesized before. Photopolymerization results indicate that BPB presented better initiation performance than that of BPH. Photolysis experiments showed that BPB reacted faster with co-initiator triethanolamine. The photophysical property and redox potential of BPH and BPB were characterized by using various technique to understand their diverse performance. Results showed that BPB displayed typical triplet absorption of benzophenone, which was not observed in BPH. In addition, BPB presented higher reduction potential, which is also beneficial to its reaction with co-initiator.