MDPI - Publisher of Open Access Journals

19 pages, 12218 KiB

Open AccessArticle

Excited-State Dynamics of Carbazole and tert-Butyl-Carbazole in Thin Films

by Konstantin Moritz Knötig, Domenic Gust, Kawon Oum and Thomas Lenzer

Photochem 2024, 4(2), 179-197; https://doi.org/10.3390/photochem4020011 - 9 Apr 2024

Cited by 3 | Viewed by 1770

Thin films of carbazole (Cz) derivatives are frequently used in organic electronics, such as organic light-emitting diodes (OLEDs). Because of the proximity of the Cz units, the excited-state relaxation in such films is complicated, as intermolecular pathways, such as singlet–singlet annihilation (SSA), kinetically [...] Read more.

Thin films of carbazole (Cz) derivatives are frequently used in organic electronics, such as organic light-emitting diodes (OLEDs). Because of the proximity of the Cz units, the excited-state relaxation in such films is complicated, as intermolecular pathways, such as singlet–singlet annihilation (SSA), kinetically compete with the emission. Here, we provide an investigation of two benchmark systems employing neat carbazole and 3,6-di-tert-butylcarbazole (t-Bu-Cz) films and also their thin film blends with poly(methyl methacrylate) (PMMA). These are investigated by a combination of atomic force microscopy (AFM), femtosecond and nanosecond transient absorption spectroscopy (fs-TA and ns-TA) and time-resolved fluorescence. Excitonic J-aggregate-type features are observed in the steady-state absorption and emission spectra of the neat films. The S₁ state shows a broad excited-state absorption (ESA) spanning the entire UV–Vis–NIR range. At high S₁ exciton number densities of about 4 × 10¹⁸ cm⁻³, bimolecular diffusive S₁–S₁ annihilation is found to be the dominant SSA process in the neat films with a rate constant in the range of 1–2 × 10⁻⁸ cm³ s⁻¹. SSA produces highly vibrationally excited molecules in the electronic ground state (S₀*), which cool down slowly by heat transfer to the quartz substrate. The results provide relevant photophysical insight for a better microscopic understanding of carbazole relaxation in thin-film environments. Full article

(This article belongs to the Special Issue Feature Papers in Photochemistry II)

► Show Figures

Graphical abstract

12 pages, 3985 KiB

Open AccessArticle

Enhanced Ultrafast Broadband Reverse Saturable Absorption in Twistacenes with Enlarged π-Conjugated Central Bridge

by Xindi Liu, Wenfa Zhou, Mengyi Wang, Xingzhi Wu, Jidong Jia, Jinchong Xiao, Junyi Yang and Yinglin Song

Molecules 2022, 27(24), 9059; https://doi.org/10.3390/molecules27249059 - 19 Dec 2022

Cited by 2 | Viewed by 2101

Abstract

Optical nonlinearities of two all-carbon twistacenes, DPyA and DPyN, with the different π-conjugated central bridges were investigated. The nonlinear absorption properties of these compounds were measured using the femtosecond Z-scan with wavelengths between 650 and 900 nm. It has been found that [...] Read more.

Optical nonlinearities of two all-carbon twistacenes, DPyA and DPyN, with the different π-conjugated central bridges were investigated. The nonlinear absorption properties of these compounds were measured using the femtosecond Z-scan with wavelengths between 650 and 900 nm. It has been found that the nonlinear absorption originated from two-photon absorption (TPA) and TPA-induced excited state absorption (ESA), wherein DPyA demonstrates higher performance than DPyN. The TPA cross section of DPyA (4300 GM) is nearly 4.3 times larger than that of DPyN at 650 nm. Moreover, the different central structures modulate the intensity of ESA at 532 nm, and DPyA exhibits an excellent ESA at 532 nm with multi-pulse excitation. Meanwhile, the result of data fitting and quantum chemistry calculation shows that the enhancement of nonlinear absorption in DPyA is due to the extended π- conjugated bridge and improved delocalization of π-electrons. These all-carbon twistacenes could yield potential applications in optical power limiting (OPL) technology. Full article

(This article belongs to the Topic Recent Advances in Nonlinear Optics and Nonlinear Optical Materials)
(This article belongs to the Section Materials Chemistry)

► Show Figures

Figure 1

1 pages, 162 KiB

Open AccessAbstract

Photophysical Studies of Poly(3,4-Ethylenedioxythiophene/Cucurbit[7]uril) Polypseudorotaxane and Polyrotaxane by Transient Absorption and Time-Resolved Fluorescence Spectroscopy

by Radu Ionut Tigoianu and Aurica Farcas

Eng. Proc. 2022, 27(1), 5; https://doi.org/10.3390/ecsa-9-13375 - 1 Nov 2022

Viewed by 1027

Abstract

The UV-Vis absorption, fluorescence, and phosphorescence spectra of poly(3,4-ethylenedioxythiophene/cucurbit[7]uril), polypseudorotaxane (1), and polyrotaxane (2) in water and acetonitrile solutions were investigated. To achieve a deeper insight into the optical properties, the transient absorptions, lifetimes, and quantum yields have been [...] Read more.

The UV-Vis absorption, fluorescence, and phosphorescence spectra of poly(3,4-ethylenedioxythiophene/cucurbit[7]uril), polypseudorotaxane (1), and polyrotaxane (2) in water and acetonitrile solutions were investigated. To achieve a deeper insight into the optical properties, the transient absorptions, lifetimes, and quantum yields have been carried out on compounds 1 and 2. The transient absorption demonstrated an excited-state processes and involvement of high energy electronic states (S_n > 1). The transient absorption map in acetonitrile revealed at 210, 240, 300, and 315 nm a ground states bleaching bands (GSB), whereas at shorter wavelengths an absorption in excited states (ESA) and more than one excited state (S_n > 1). At 382 and 420 nm wavelength two negative bands appeared which were assigned to the stimulated emissions (SE). At longer wavelengths, i.e., 605, 625, and 710 nm, other stimulated emissions appeared that are probably a result of the triplet manifold, confirming their phosphorescence properties. Additionally, the quantum yield with absolute values in the range 5–25%, and phosphorescence lifetime with values in the range 1–9 μs were evaluated. Full article

(This article belongs to the Proceedings of The 9th International Electronic Conference on Sensors and Applications)

1 pages, 168 KiB

Open AccessAbstract

Photophysical Properties of Some Naphthalimide Derivatives

by Radu Ionut Tigoianu, Anton Airinei, Florentina Georgescu, Alina Nicolescu and Calin Deleanu

Eng. Proc. 2022, 27(1), 4; https://doi.org/10.3390/ecsa-9-13356 - 1 Nov 2022

Cited by 1 | Viewed by 1131

Abstract

Naphthalimide derivatives possess many interesting properties such as strong emission, high quantum efficiency, good photostability, thermal stability, etc. The electronic absorption and fluorescence spectra of naphthalimides are sensitive to the polarity of surrounding environment, and these derivatives can be excellent candidates for fluorescent [...] Read more.

Naphthalimide derivatives possess many interesting properties such as strong emission, high quantum efficiency, good photostability, thermal stability, etc. The electronic absorption and fluorescence spectra of naphthalimides are sensitive to the polarity of surrounding environment, and these derivatives can be excellent candidates for fluorescent sensors for water detection in solution because the emission is strongly depended on the solvent polarity and it is quenched even at low water levels. In order to find out more information about the excited state dynamics of the naphthalimide derivatives, time-resolved fluorescence experiments were conducted in solvents of different polarities, and lifetimes from 0.5 ns to 9 ns were obtained. The transient absorption map in dioxane, dimethylformamide and methanol in the presence or absence of water revealed ground state bleaching bands (GSB) in the range of 230–290 nm, whereas an absorption band in excited state (ESA) occurred at shorter wavelengths from 210 to 295 nm. At longer wavelength, negative bands appeared, which can be assigned to the stimulated emissions (SE). In addition, the quantum yields with absolute values from 0.01 to 0.87 were found depending on the solvent nature. Full article

(This article belongs to the Proceedings of The 9th International Electronic Conference on Sensors and Applications)

18 pages, 7849 KiB

Open AccessCommunication

An Efficient Aequorea victoria Green Fluorescent Protein for Stimulated Emission Depletion Super-Resolution Microscopy

by Barbara Storti, Benedetta Carlotti, Grazia Chiellini, Martina Ruglioni, Tiziano Salvadori, Marco Scotto, Fausto Elisei, Alberto Diaspro, Paolo Bianchini and Ranieri Bizzarri

Int. J. Mol. Sci. 2022, 23(5), 2482; https://doi.org/10.3390/ijms23052482 - 24 Feb 2022

Cited by 3 | Viewed by 3216

Abstract

In spite of their value as genetically encodable reporters for imaging in living systems, fluorescent proteins have been used sporadically for stimulated emission depletion (STED) super-resolution imaging, owing to their moderate photophysical resistance, which does not enable reaching resolutions as high as for [...] Read more.

In spite of their value as genetically encodable reporters for imaging in living systems, fluorescent proteins have been used sporadically for stimulated emission depletion (STED) super-resolution imaging, owing to their moderate photophysical resistance, which does not enable reaching resolutions as high as for synthetic dyes. By a rational approach combining steady-state and ultrafast spectroscopy with gated STED imaging in living and fixed cells, we here demonstrate that F99S/M153T/V163A GFP (c3GFP) represents an efficient genetic reporter for STED, on account of no excited state absorption at depletion wavelengths <600 nm and a long emission lifetime. This makes c3GFP a valuable alternative to more common, but less photostable, EGFP and YFP/Citrine mutants for STED imaging studies targeting the green-yellow region of the optical spectrum. Full article

(This article belongs to the Special Issue Naturally Derived Macromolecular Compounds for Biomedical, Pharmaceutical, Cosmetic, and Food Applications - in Memory of Professor Federica Chiellini)

► Show Figures

Figure 1

20 pages, 2901 KiB

Open AccessReview

Progress and Summary of Photodarkening in Rare Earth Doped Fiber

by Tianran Sun, Xinyang Su, Yunhong Zhang, Huaiwei Zhang and Yi Zheng

Appl. Sci. 2021, 11(21), 10386; https://doi.org/10.3390/app112110386 - 5 Nov 2021

Cited by 14 | Viewed by 6166

Abstract

In this paper, we summarize the research on photodarkening in optical fibers. The causes of photodarkening in fiber, the influence of photodarkening on fiber laser, the experimental device of photodarkening, and the mathematical model used to study the phenomenon of photodarkening are described [...] Read more.

In this paper, we summarize the research on photodarkening in optical fibers. The causes of photodarkening in fiber, the influence of photodarkening on fiber laser, the experimental device of photodarkening, and the mathematical model used to study the phenomenon of photodarkening are described in detail. At the end of the paper, we summarize the means and methods to suppress photodarkening. Full article

► Show Figures

Figure 1

12 pages, 3573 KiB

Open AccessArticle

Upconversion Visible Light Emission in Yb/Pr Co-Doped Yttria-Stabilized Zirconia (YSZ) Single Crystals

by Daini Wang, Wenxia Wu, Xiaojun Tan, Bernard A. Goodman, Shoulei Xu and Wen Deng

Crystals 2021, 11(11), 1328; https://doi.org/10.3390/cryst11111328 - 31 Oct 2021

Cited by 8 | Viewed by 2555

Abstract

As a development on previous research on single crystals of Pr³⁺-doped yttria-stabilized zirconia (YSZ), we report here the preparation and optical properties of Yb/Pr co-doped YSZ single crystals with different Yb₂O₃ concentrations. Results from X-ray diffraction (XRD) and [...] Read more.

As a development on previous research on single crystals of Pr³⁺-doped yttria-stabilized zirconia (YSZ), we report here the preparation and optical properties of Yb/Pr co-doped YSZ single crystals with different Yb₂O₃ concentrations. Results from X-ray diffraction (XRD) and Raman spectroscopy indicated that all of the crystal samples had a cubic phase structure, and transmission was ≥88% in the 550–780 nm range. Photoluminescence (PL) under excitation with a 980 nm laser showed upconversion emission, and several peaks were observed centered on 448 nm, 508 nm, 525 nm, 542 nm, 617 nm and 656 nm. The effects of excited state absorption (ESA), energy transfer upconversion (ETU), cross relaxation (CR), and cooperative energy transfer (CET) on the upconversion luminescence and energy transition mechanism in YSZ crystals were further studied. The fluorescence lifetime of the ³P₀ → ³H₅ transition at 542 nm reached 207 μs, which shows that the samples are of potential use for laser and fluorescence output. Full article

► Show Figures

Graphical abstract

14 pages, 2644 KiB

Open AccessArticle

Optical Transitions and Excited State Absorption Cross Sections of SrLaGaO₄ Doped with Ho³⁺ Ions

by Marcin Kaczkan and Michał Malinowski

Materials 2021, 14(14), 3831; https://doi.org/10.3390/ma14143831 - 8 Jul 2021

Cited by 6 | Viewed by 2586

Abstract

The spectroscopic properties of SrLaGaO₄ (SLO) crystal doped with Ho³⁺ ions were studied in this work. Absorption, emission spectra and decay dynamics of excited states have been measured and discussed using the Judd–Ofelt model. Photoluminescence emissions were attributed to transitions from [...] Read more.

The spectroscopic properties of SrLaGaO₄ (SLO) crystal doped with Ho³⁺ ions were studied in this work. Absorption, emission spectra and decay dynamics of excited states have been measured and discussed using the Judd–Ofelt model. Photoluminescence emissions were attributed to transitions from the excited ³D₃, ⁵S₂, ⁵F₅, ⁵I₆ and ⁵I₇ multiplet manifolds. The experimental lifetimes for five excited states have been compared to the theoretical values, calculated using Judd–Ofelt theory, allowing for the determination of the multiphonon relaxation rates (W_nR) of the respective states. The experimental data were approximately on a line expressed by W_nR = W₀ exp(−αΔE) with W₀ = 0.5 × 10⁷ s⁻¹ and α = 2.6 × 10⁻³ cm. To discuss the excited state absorption (ESA) pathways, that originated from several excited levels, we used the Judd–Ofelt formalism allowing determination of the integrated cross section for ESA transitions. Full article

(This article belongs to the Special Issue Trends in Electronic and Optoelectronic Materials)

► Show Figures

Figure 1

15 pages, 2144 KiB

Open AccessArticle

An Optical Power Limiting and Ultrafast Photophysics Investigation of a Series of Multi-Branched Heavy Atom Substituted Fluorene Molecules

by Hampus Lundén, Delphine Pitrat, Jean-Christophe Mulatier, Cyrille Monnereau, Iulia Minda, Adrien Liotta, Pavel Chábera, Didrik K. Hopen, Cesar Lopes, Stéphane Parola, Tönu Pullerits, Chantal Andraud and Mikael Lindgren

Inorganics 2019, 7(10), 126; https://doi.org/10.3390/inorganics7100126 - 18 Oct 2019

Cited by 3 | Viewed by 3198

Abstract

A common molecular design paradigm for optical power limiting (OPL) applications is to introduce heavy atoms that promote intersystem crossing and triplet excited states. In order to investigate this effect, three multi-branched fluorene molecules were prepared where the central moiety was either an [...] Read more.

A common molecular design paradigm for optical power limiting (OPL) applications is to introduce heavy atoms that promote intersystem crossing and triplet excited states. In order to investigate this effect, three multi-branched fluorene molecules were prepared where the central moiety was either an organic benzene unit, para-dibromobenzene, or a platinum(II)–alkynyl unit. All three molecules showed good nanosecond OPL performance in solution. However, only the dibromobenzene and Pt–alkynyl compounds showed strong microsecond triplet excited state absorption (ESA). To investigate the photophysical cause of the OPL, especially for the fully organic molecule, photokinetic measurements including ultrafast pump–probe spectroscopy were performed. At nanosecond timescales, the ESA of the organic molecule was larger than the two with intersystem crossing (ISC) promoters, explaining its good OPL performance. This points to a design strategy where the singlet-state ESA is balanced with the ISC rate to increase OPL performance at the beginning of a nanosecond pulse. Full article

(This article belongs to the Special Issue Organometallic and Coordination Compounds for Optical and Energy-Related Applications)

► Show Figures

Graphical abstract

Search Results (9)

Further Information

Guidelines

MDPI Initiatives

Follow MDPI

Saved Queries

Search Filter Reset All

Years

Feature Papers

Subjects

Journals

Article Types

Countries / Regions

Search Results (9)

Further Information

Guidelines

MDPI Initiatives

Follow MDPI