ChemPhotoChem最新文献

This work reviews new ideas developed in the last two decades which play a key role for understanding the optical properties of insulating materials containing transition metal (TM) cations. Initially, this review deals with compounds involving d⁴ and d⁹ ions where the local structure of the involved MX₆ complexes (M=dⁿ cation, X=ligand) is never cubic but distorted, a fact widely ascribed to the Jahn-Teller (JT) effect. Nevertheless, that assumption is often wrong as the JT coupling requires an orbitally degenerate ground state in the initial geometry a condition not fulfilled even if the lattice is tetragonal. For this reason, the equilibrium geometry of d⁴ and d⁹ complexes in low symmetry lattices, is influenced by two factors: (i) The effects, usually ignored, of the internal electric field, E_R, due to the rest of lattice ions on the active electrons localized in the MX₆ unit. (ii) The existence of structural instabilities driven by vibronic interactions that lead to negative force constants. As first examples of these ideas, we show that the equilibrium structure, electronic ground state of KZnF₃:Cu²⁺, K₂ZnF₄:Cu²⁺ and K₂CuF₄ obey to different causes and only in KZnF₃:Cu²⁺ the JT effect takes place. These ideas also explain the local structure and optical properties of CuF₂, CrF₂ or KAlCuF₆ compounds where the JT effect is symmetry forbidden and those of layered copper chloroperovskites where the orthorhombic instability explains the red shift of one d−d transition under pressure. In a second step, this review explores stable systems involving d³, d⁵ or d⁹ cations, where the internal electric field, E_R, is responsible for some puzzling phenomena. This is the case of ruby and emerald that surprisingly exhibit a different color despite the Cr³⁺-O²⁻ distance is the same. A similar situation holds when comparing the normal (KMgF₃) and the inverted (LiBaF₃) perovskites doped with Mn²⁺ having the same Mn²⁺-F distance but clearly different optical spectra. The role of E_R is particularly remarkable looking for the origin of the color in the historical Egyptian Blue pigment based on CaCuSi₄O₁₀.

The Front Cover illustrates the molecular structures of coumarin-caged ryanodine receptor (RyR) agonists and blockers. Photo-irradiation of a (6-bromo-7-hydroxycoumarin-4-yl)methyl (Bhc)-caged agonist released the active form, activated RyRs, and promoted Ca²⁺ release from the endoplasmic reticulum in mammalian cells. The photoreactivity of the caged RyR probes by 405 nm light was masked by the enzyme substrates, allowing cell-type-selective, enzyme gene-directed delivery of the caged RyR probes. More information can be found in the Research Article by A. Yokoyama, H. Aoki, T. Furuta et al. (DOI 10.1002/cptc.202400140).

Bright deep-NIR dyes are actively sought after for their potential in fluorescence-guided surgery and disease theranostics. The major bottleneck lies with the rigidification of the conjugative backbone to suppress non-radiative deactivation. EC5 is a notable deep-NIR absorbing/emitting scaffold, which we first reported in 2017. We recently discovered that its diphenyl ether moiety exhibited structural freedom, which was detrimental to its fluorescence brightness. We proposed to enhance the structural rigidity of EC5 via ring-contraction, i. e., changing the diphenyl ether moiety of EC5E into a biphenyl of EC5B, its low-frequency normal modes were largely suppressed as predicted by theoretical calculations, and a 55.0 % increase of fluorescence brightness in CH₂Cl₂ was rendered experimentally. The bright EC5B was feasible for high-contrast in vivo imaging. EC5B has broad potential in practical biomedical applications.

Rhodamine dyes have been extensively explored for bioimaging and therapeutic applications over the past few decades. However, it remains a challenge to design long-wavelength and large Stokes shift rhodamine derivatives to meet the requirements of fluorescence imaging and phototherapy in deep living tissues. In this work, a pyridine aromatic unit was inserted into the rhodamine derivatives (AC-Fluor: ACF) skeleton to prepare a series of stable rhodamine derivatives, named ACFPs, to achieve long emission wavelength (>650 nm) and large Stokes shift (~60 nm) by tuning the conjugated systems and electronic symmetry. Moreover, ACFPs are capable of continuously producing superoxide radical (O₂⁻⋅) under long wavelength irradiation. This study presents a novel paradigm for improving the optical properties of rhodamine, which has led to the development of a novel tool for image-guided phototherapy for cancer treatment.

Natural ion-transporters in cellular membranes play a critical role in maintaining cell homeostasis. Synthetic ion-transporters are attractive model systems for understanding and addressing dysfunction of natural transporters. Herein, a simple amide derived from azobenzene and m-aminobenzoic acid achieves photoregulated ion transport across lipid membranes. The amide forms pores or channels that selectively co-transport H⁺/X⁻ across the lipid membrane. Photoisomerization from the trans to cis form results in a 2-fold increase in ion-transport rates due to the higher proton affinity of the cis isomer.

Triplet-triplet annihilation upconversion (TTA-UC) technology could convert low-energy light into high-energy light, and it is a very promising one of the upconversion technologies due to its non-coherent excitation light, low required excitation optical power density and sensitizer/annihilator flexible adjustability. The application of TTA-UC into photocatalysis could not only broaden the range of solar energy spectrum utilization, but also bring mild reaction conditions and higher product yields via avoiding the side reaction. However, the detailed catalytic mechanism of TTA-UC is unclear. Therefore, in this review, we summarized and classified TTA-UC photocatalytic chemical reactions in terms of mechanism.

In an era marked by a growing emphasis on sustainability and innovation, the quest for eco-friendly solutions to energy conversion devices capable of harnessing visible light has gained paramount importance. In response to this critical demand, we demonstrate visible light-responsive photoswitching from molybdenum trioxide nanobelt arrays in the photoconductive device fabricated using solution-processing technique. We exploit the visible light-driven modulation of conductivity in the reversibly switchable photochromic state of MoO₃ to develop a photochromism-assisted photoconductive photodetector with fast response (<0.1 s), significant photocurrent on/off ratio and excellent responsivity (41 AW⁻¹ at 459 nm) under the applied bias of 5 V. The light harvesting strategy presented herein holds the potential for efficient energy generation by harnessing visible light, even under low-light conditions.

This article reports a detailed mechanistic and kinetic study of an unusual photoreaction leading to the (diazonia)tetrabenzonaphthacene skeleton. The photo-triggered double intramolecular nucleophilic aromatic substitution (S_NAr*) has been investigated by varying the leaving groups. Photoreaction quantum yields have been determined and mechanistic insights have been supported by theoretical calculations using DFT and TD-DFT methods. Additionally, we show that this light-triggered formed diazonia constitutes a potent photosentitizer with a singlet oxygen generation quantum yield of 0.55, both in organic solvents and in water, which is an extremely relevant value in view of PDT applications or use as an oxidation photocatalyst in aqueous media. Once again, the experimental observations were supported by TD-DFT calculations showing a large density of triplet states below the S₁ excited state along with large spin-orbit couplings. The reaction is not restricted to solutions but can also occur in solid PDMS matrices thus allowing for photochemical encoding of information that will progressively vanish upon prolonged UV-exposure.

π−π stacking interactions are generally thought to reduce the luminescence of materials. Here, a systematic investigation is conducted using a π−π stacking dimer with varying steric hindrance substituents as a model to illustrate how π−π stacking structure affects the luminescence efficiency of materials. Four naphthalimide (NI) derivative molecules were designed and synthesized by incorporating sterically hindered unilateral groups to achieve NIPH, NIP1C, NIP2C, and NIP3C. It was figured out that side group modification did affect their crystal packing structures and luminescent properties. On the one hand, the excimer state formed by strongly interacted π−π NI-based dimer (NIPH and NIP3C) enhances luminescence efficiency compared to the monomer state based on weakly interacted π−π NI-based dimers (NIP1C and NIP2C). On the other hand, the discrete stacking of NI-based dimers (NIP3C) further promotes luminescence efficiency compared to the nondiscrete stacking of NI-based dimers (NIPH). Among these four compounds, NIP3C exhibits discrete stacking of π−π NI-based dimer due to the large steric hindrance generated by propyl benzene, resulting in the highest luminescence efficiency of the NIP3C crystal. This work will provide further insight into the underlying mechanisms behind the high luminescence efficiency induced by π−π dimer stacking.

This work introduces a novel ternary heterostructure as a photocatalyst to selectively produce benzaldehyde from benzyl alcohol through photooxidation. We have synthesized bismuth vanadate functionalized graphitic carbon nitride decorated reduced graphene oxide B/CN@rGO ternary composite and subsequently subjected it to several characterization methodologies like XRD, FE-SEM, HR-TEM, XPS, FT-IR, TGA, UV-vis DRS, and EIS. The synthesized B/CN@rGO was effectively used in the photooxidation process to produce benzaldehyde from benzyl alcohol, employing a cost-effective white LED light of 200 W. Remarkable selectivity (100 %) towards the benzaldehyde was attained employing green oxidant H₂O₂. In addition, the synthesized photocatalyst showed unique thermal stability and could be reused for over five cycles without compromising the selectivity of the resulting product. Based on our comprehensive review of the existing study, the present work introduces a unique approach for the photooxidation of benzyl alcohol, employing B/CN@rGO ternary heterostructure as the photocatalyst.