Category Archives: ChemPhotoChem

Investigating Ultrafast Electron Transfer in Graphene and Its Derivatives Composites by Femtosecond Transient Absorption Spectroscopy

Posted on 12 February 2024 by

D−A composites prepared from graphene and its derivatives (GNDs) with photo-sensitizers play an essential role in solar energy conversion. This review summarizes the recent progresses in characterizing GNDs-based composites using transient absorption spectroscopy (TAS) to assess the electronic properties of composites from a photophysical perspective. These enable the design of various more efficient solar energy conversion composites.

Abstract

As excellent functional materials, the composite materials based on graphene and its derivatives (GNDs) have lots of important application values in the emerging fields such as solar energy conversion, and the exploration of electron (or energy) transfer properties of those composites is the key for revealing their further applications. In this review, femtosecond transient absorption spectroscopy (TAS) has been introduced as an essential technique to understand the carrier behaviors in GNDs composites, as well as the advancements of TAS. The specific examples of electron transport in various composite materials characterized by TAS are summarized and discussed, which consist of GNDs with semiconductor quantum dots (QDs), organic dyes, organic polymers, perovskites and other materials, respectively. This review provides a deep insight into the electron transfer (ET) kinetics of various GNDs composites from the perspective of TAS.

Enhance the efficiency of perovskite solar cells using W doped SnO2 electron transporting layer

Posted on 12 February 2024 by

High quality W doped SnO₂ electron transporting layer is prepared using molecular precursor containing SnC₂O₄ and (NH₄)₁₀W₁₂O₄₁ ⋅ xH₂O, which could effectively modify the electric conductivity and energy band position of resulting SnO₂ film. Therefore, power conversion efficiency of the perovskite solar cells with W doped SnO₂ layer are impressively promoted.

Abstract

For low temperature (≤180 °C) processed perovskite solar cells (PSCs), SnO₂ has been proven to be one of the most effective electron transporting layer. However, problems, such as poor electric conductivity and high defect density, inevitably exist in the SnO₂ films which are fabricated using low temperature solution methods. Element doping of SnO₂ film is a feasible strategy to alleviate the above problems. Herein, W doping of the SnO₂ is realized through addition of ammonium tungstate hydrate into the molecular precursor of SnO₂. The W doped SnO₂ film exhibits higher conductivity, and can better extract and transport the electrons from the perovskite films. Hence, power conversion efficiency is boosted from 20.60 % for the reference PSCs to 21.83 % for PSCs fabricated on 2.5 mg mL⁻¹ ammonium tungstate hydrate doped SnO₂ films.

Chemical and photophysical properties of amine functionalized bis‐NHC‐pyridine‐RuII complexes

Posted on 12 February 2024 by

Amine substitution in the backbone of a room temperature (r. t.) luminescent C^N^C ruthenium(II) complex alters the excited energy landscape such that at low temperature (l.t.) the typical luminescent relaxation of the ³MLCT (metal-to-ligand charge transfer) to the ¹GS (ground state) can occur, but at r. t. a dark relaxation pathway across the ³MC (metal centered) state is activated and a higher photostability is observed.

Abstract

The effects of backbone amine functionalization in three new homoleptic C^N^C type ruthenium(II) complexes bearing a tridentate bis-imidazole-2-ylidene pyridine ligand framework are characterized and studied by single crystal diffraction, electrochemistry, optical spectroscopy and transient absorption spectroscopy in combination with ab initio DFT calculations. Functionalization by dimethylamine groups in 4-position of the pyridine backbone significantly influences the properties of the complexes as revealed by comparison with the unfunctionalized references. As a result of the amine functionalization, a higher molar absorption coefficient of the MLCT bands, a decreased photoluminescence quantum yield at room temperature together with a shortened excited state lifetime but an improved photostability is observed. Introduction of electron donating and withdrawing groups at the NHC unit modifies the electronic and optical properties, such as the oxidation potential, absorption and emission properties, and the lifetimes of the excited states.

5‐Aryl Substituted 2‐(2‐Methoxyphenyl)benzoxazoles with Large Stokes Shifts: Synthesis, Crystal Structures and Optical Properties

Posted on 8 February 2024 by

Unlike 2-(2-hydroxyphenyl)benzoxales (HBOs), 2-(2-methoxyphenyl)benzoxazoles (MBOs) lack the sought-after large Stokes shifts of the former which are necessary in fluorescence microscopy. Herein, we demonstrate that the 5-aryl substitution of MBOs affords 2-(4-methoxy-[1,1’-biphenyl]-3-yl)benzoxazoles (MBBOs) dyes with large Stokes shifts.

Abstract

2-(2-methoxyphenyl)benzoxazole (MBO) displays similar photophysical properties to 2-(2-hydroxyphenyl)benzoxazole (HBO), but it lacks the large Stokes shifts necessary for fluorescence microscopy applications. In this paper, we report the 5-substitution of MBO with aryl groups to produce 2-(4-methoxy-[1,1’-biphenyl]-3-yl)benzoxazoles (MBBOs) with large Stokes shifts. The synthesis of MBBOs 6–15 was accomplished in moderate to good yields by microwave-assisted Sonogashira cross couplings. Crystal structures for compounds 6–9 and 15 are provided. MBBOs 6–10, 12, and 14 displayed considerably blue-shifted absorption maxima and slight bathochromic shifts of their fluorescence maxima relative to the unsubstituted MBO.

Corrigendum: Time‐Resolved CIDNP as a Tool for Determination of Rate Constants of Triplet Quenching Using the Example of Photo‐Induced Oxidation of Histidine‐Containing Compounds

Posted on 6 February 2024 by Wiley: ChemPhotoChem: Table of Contents

ChemPhotoChem, EarlyView.

Converting Conventional Host to TADF Sensitizer and Hot‐Exciton Emitter in Donor‐Adamantane‐Acceptor Triads for Blue OLEDs: A Computational Study

Posted on 5 February 2024 by nRamalingam Mahaan, nAruljothy John Bosco, nA. Irudaya Jothin

TADF Sensitizer and Hot-Exciton Emitter: The conventional host molecule undergoes a conversion into a TADF sensitizer and a Hot-Exciton emitter via distinct donor and acceptor unit substitutions on the adamantane core. Molecules incorporating acceptor units such as DMB and BODIPY, which feature boron atoms, have the potential to serve as TADF sensitizers and Hot-exciton emitters for OLED applications, respectively.

Abstract

Exploiting triplet excitons in TADF sensitizers and hot-exciton emitters has attracted considerable attention and interest in recent studies on the design and development of blue OLEDs. The structural and optical property relationship of adamantane (Ad) core appended with four different strengths of donor and seven acceptor units were investigated using DFT and TD-DFT methods. The theoretical studies revealed that increased donor and acceptor strength on adamantane building block leads to: (i) a decrease in ionization potentials and an increase in electron affinities, (ii) a decrease in singlet energies (E_S) and the S₁-T₁ energy gaps (ΔE_ST); (iii) decreased SOC magnitudes between S₁-T₁ states; (iv) increased RISC rate from the T_n to S₁ states, demonstrating an increased tendency for upconversion of triplet excitons from the T_n to S₁ state. In addition, low exchange energy causes excited state characteristics of molecules to shift from HLCT to CT nature in the S₁ state. In contrast, the T₁ states retain their LE character, resulting in higher triplet energies (E_T). The adamantane molecular systems appended with P-DMAC-Donor-Ad-P-DMB and Donor-Ad-P-BODIPY based triads exhibit promising TADF sensitizer and hot-exciton characteristics to find application as potential candidates for blue OLEDs when compared to experimentally reported conventional host.

Efficient Solid‐State Ultraviolet Emission of 2′,5′‐Dioxy‐p‐terphenyls

Posted on 2 February 2024 by nMasaki Shimizu, nKenta Nishimura, nAoi Okusa, nTsuneaki Sakurain

Introduction of two alkoxy/siloxy groups at the 2′ and 5′-positions of p-teraryls has been demonstrated to be an effective molecular design strategy for developing fluorophores that exhibit efficient solid-state ultraviolet (UV) emission. The designed p-teraryls emitted UV light in the solid state at wavelengths of 362–391 nm, with quantum yields of 0.20 to 0.46.

Abstract

Organic fluorophores that efficiently emit ultraviolet (UV) light in the solid state are expected to accelerate the development of potentially attractive UV-OLEDs. Herein, we demonstrate that 2′,5′-dialkoxy-, 2′,5′-bis(siloxy)-, and 2′-(alkoxy)-5′-(siloxy)-p-terphenyls and 2,5-dioxy-1,4-(1-naphthyl)benzenes are efficient UV-emitting solid fluorophores. The teraryls were prepared by a Pd-catalyzed Suzuki–Miyaura cross-coupling reaction of readily available 2,5-dialkoxy-1,4-diiodobenzenes with phenyl- and (1-naphthyl)boronic acid, followed by dealkylation–silylation. The dioxy-p-teraryls are thermally stable, with some having glass transition temperatures ranging from −8 to 47 °C. Single-crystal X-ray diffraction analysis of 2′,5′-bis(triphenylsiloxy)- and 2′-(hexyloxy)-5′-(triphenylsiloxy)-p-terphenyls revealed that the terphenyl moieties adopted twisted conformations, and there were no intramolecular π–π interactions in the crystal packing. The terphenyls in CH₂Cl₂ fluoresced at 370–386 nm with quantum yields of 0.30–0.44. Efficient UV emission (362–391 nm) of the teraryls was observed in the solid state, with quantum yields of 0.20–0.46. Density functional calculations suggest that the optical excitation of the terphenyls involves intramolecular charge transfer from the ethereal oxygen, with the moieties accepting the charge transfer depending on the substituents on the ethereal oxygen atoms.

Revisiting the Chemistry and Photophysics of 3‐(N‐Methylpyridinium‐4‐yl)Coumarins for Designing “Covalent‐Assembly” and “Molecular Disassembly” Fluorescent Probes

Posted on 30 January 2024 by

The double face of N -methylpyridinium moiety!!! Synthesis and photophysics of 7-(diethylamino)/7-hydroxycoumarins bearing N-methylpyridinium-4-yl group as C3 substituent were studied for identifying novel fluorophores usable in activity-based sensing approaches. The unexpected weak emissive properties of the 7-hydroxycoumarin derivative in neutral aqueous media was rationalized. Superior fluorescence performances observed with 7-(diethylamino) counterpart and ortho-formylated derivative led us to consider the design of two novel reaction-based fluorescent probes responsive to alkaline phosphatase enzyme and pyrophosphate ions respectively.

Abstract

The constant need for high-performance aniline- or phenol-based fluorophores suitable for the construction of activity-based fluorescent probes, led us to study both synthesis and photophysics of C3-N-methylpyridinium-4-yl substituted 7-(dialkylamino)/7-hydroxycoumarins. Indeed, in the field of photoactive organic molecules, the positively charged N-alkylpyridinium-4-yl groups are often used as acceptor units to dramatically impact spectral features through promoting intramolecular charge transfer (ICT) processes. They are also known as effective water-solubilizing and mitochondria targeting moieties. The poor fluorescence efficiency of cationic 7-hydroxycoumarin derivatives in aqueous physiological conditions was highlighted and rationalized by the predominance of a neutral quinonoid form in such buffer medium. The ability of the excited singlet state (S₁) of this neutral species to undergo intersystem crossing (ISC) to triplet state (T₁) was partly supported by phosphorescence measurements of singlet oxygen. We also took advantage of green-emissive properties of 7-(diethylamino)-3-(N-methylpyridinium-4-yl)coumarin to successfully design and validate a novel small-molecule fluorescent probe for the detection of alkaline phosphatase (ALP), based on the “covalent-assembly” principle. A practical use of ortho-formylated 7-hydroxy-3-(N-methylpyridinium-4-yl)coumarin was next considered with the synthesis of a Fe(III)-salen complex whose the potential as a “molecular disassembly” probe for fluorogenic sensing of pyrophosphate (PPi) anion was assessed.

A Guide to Chemical Reactions Design in Carbon Nitride Photocatalysis

Posted on 29 January 2024 by nOleksandr Savateev, nJingru Zhuangn

This article provides general guidelines, which are used to design photocatalytic organic transformations using graphitic carbon nitrides. It includes discussion of the local chemical structure of carbon nitride excited state, its redox potentials and the redox potentials of the reagents, and the chemical reactivity of the open-shell intermediates.

Abstract

Graphitic carbon nitride semiconductors are inexpensive and reusable photocatalysts, which are actively studied in organic synthesis. Successful design of photocatalytic reactions is based on the next considerations. i) Thermodynamic feasibility of photoinduced processes, which involve transfer of electrons or electron-proton couples. ii) Redox activity of reagents. iii) Reactivity of the open-shell intermediates generated from the reagents. Herein, we summarize current understanding of how local chemical structure of graphitic carbon nitrides and their redox potentials are used to design photocatalytic reactions. This work intends to serve as a guideline for materials scientists, who are willing to apply their carbon nitride semiconductors in reactions involving organic substrates, and for organic chemists, who are interested to dive into heterogeneous carbon nitride photocatalysis.

Charge‐Transfer Modulation of Emissivity in Polarized Diketopyrrolopyrroles

Posted on 26 January 2024 by

Modulation of strength and position of electron-donating substituent directly linked to a diketopyrrolopyrrole core offers an interesting approach towards fine-tuning their photophysics. Depending on the type of cyclic tertiary aromatic amine either Franck-Condon or charge-transfer excited states have the lowest energy. The N-carbazolyl substituent enables DPPs to have very strong fluorescence while other donors such as phenothiazine red-shift the emission at the expense of quantum yield.

Abstract

Strongly polarized donor-acceptor-donor′ diketopyrrolopyrroles, differing in the type of key donor moiety, were designed and synthesized to examine how this affects the non-radiative decay. Dyes possessing less electron-rich N-carbazolyl substituents are characterized by strong yellow emission from a locally excited (LE) state, whereas replacing this donor with more electron-rich N-phenothiazinyl substituent changes the relative position of charge-transfer (CT) and LE states, leading to weaker, reddish-orange fluorescence. As a result, there is solvent-dependent charge-transfer emission shifted to as far as 700 nm. The opening of the intersystem crossing channel to the triplet state possessing CT character is the most likely cause of the fluorescence quantum yield variation in some cases. These results reveal that the fate of molecules in their excited state can be fine-tuned by very small structural changes.