ChemPhotoChem最新文献

Switchable intersystem crossing (sISC) is a novel concept in the design of functional dyes that enables dynamic modulation of fluorescence and triplet state formation in response to changes in the dye's environment. Unlike conventional dyes, where intersystem crossing and fluorescence rates are entirely determined by molecular structure, sISC dyes allow reversible switching between these functions based on external factors, such as solvent polarity. sISC can arise from various photophysical mechanisms involving charge–transfer states, whose energies are sensitive to the surrounding environment. Mechanisms such as thermally activated delayed fluorescence and spin–orbit charge transfer intersystem crossing can be employed to design sISC dyes. The ability to fine-tune photophysical processes without chemical modification of the dye's structure opens new possibilities for biomedical applications, including bioimaging, photodynamic therapy, and optogenetic control. This paper introduces the concept of sISC, provides key examples of dyes exhibiting this behavior, and discusses approaches for their design.

Chiral copolymer thin films show a strong chiroptical response, in the present study with values for the circular dichroism (CD) reaching up to 16,000 mdeg and a dissymmetry parameter, g_abs, of up to 0.7. This behavior renders these films highly attractive for optoelectronic applications, such as OLEDs with intrinsic circularly polarized emission. Such films of the achiral copolymer poly-[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (shortly, F8BT) blended with helicene-like chiral inducers are investigated. These films exhibit a unique sign inversion effect of the CD and the circularly polarized luminescence (CPL) signals as a function of film thickness (with a threshold of about 100 nm) and annealing temperature (with a threshold of about 150 °C). It is shown that structural reorganization of the chiral supramolecular phase is the most likely reason for this effect. Detailed measurements of the CPL spectra as a function of the detection angle underline the importance of detecting the emission at normal incidence to the polymer surface to avoid distortion of the CPL signal, which is otherwise identified by a bisignate CPL response at larger detection angles due to waveguide emission from the edge of the polymer film.

The long-lived radical R6G^•, derived from the cationic dye rhodamine 6G (R6G⁺) by reduction, is of growing interest in photoredox catalysis. This manuscript discusses three methods of its preparation in dimethylsulfoxide, highlighting spectral differences due to solvatochromism, co-solutes, and the basicity of the solution. Upon excitation, R6G^•* can release an electron to a substrate molecule or as a solvated electron, leading back to R6G⁺. However, a second reduction of R6G^• is not observed to be reversible here, decreasing the overall concentration of R6G^• and R6G⁺ with time. R6G⁺ can also be deprotonated to R6G1 under basic conditions, and even double deprotonation to R6G2⁻ is possible, though this may undergo irreversible reaction over time. Excitation of R6G1 leads to the formation of a photoproduct stable for seconds, which then reforms R6G1. If R6G^• is exposed to basic conditions in the presence of oxygen, it is oxidized to R6G⁺, which is then quickly deprotonated to yield R6G1 again. Hence, in basic solution, R6G1 is the predominant species, so that other light-induced reaction pathways than with R6G⁺ are accessible. It remains to be determined whether the photoproduct of R6G1 could be beneficial for a photocatalytic application under strongly basic conditions.

Dye-sensitized solar cells (DSSCs) have remained a promising alternative in photovoltaic technology due to their cost-effectiveness and adaptability to low-light conditions. Among the various sensitizers, subphthalocyanines (SubPcs) have emerged as potential candidates due to their nonflat structure, which reduces aggregation and increases solubility. However, their application in DSSCs remains poorly explored. In this study, four new SubPc dyes with different peripheral substituents are synthesized and characterized to evaluate their photovoltaic performance. The best-performing dye, SubPc 3, exhibits the most redshifted absorption spectrum and achieved a maximum efficiency of 1.69%. Photophysical analyses are conducted using transient absorption spectroscopy and intensity-modulated photovoltage/photocurrent spectroscopy (IMVS/IMPS). IMVS/IMPS measurements indicate a relatively stable electron population in the semiconductor, with an electron lifetime in the semiconductor significantly longer than the transport time, which leads to a satisfactory charge collection efficiency (η_cc = 0.83). However, ps-TAS analysis reveals efficiency losses due to competing geminate recombination (τ_grec = 1.264 µs) with the dye regeneration (τ_reg = 0.594 µs) at the origin of photogenerated current limitations. This study provides a basis for future research on SubPc sensitizers, highlighting the importance of mitigating recombination pathways to maximize light absorption and charge separation.

Subtle modification on chemical structures plays a key role in determining aggregate morphology and mechanofluorochromic (MFC) behaviors. Herein, aggregation-induced emission (AIE)-active tetraphenylethene-functionalized vinylogous-dicyano aryl derivatives with different of N-substituent groups (T-1: R=-H and T-M: R=-CH₃) have been designed and synthesized, and systematically investigated the effect of substituents on their aggregate morphology and MFC behavior. The single crystal X-ray analysis and density functional theory calculations illustrate that T-1 and T-M exhibit clear twisted spatial conformations and intramolecular charge transfer (ICT) characteristics. Meanwhile, T-1 and T-M show completely opposite directions of emission shifts after grinding. The T-1 exhibits obvious blue-shift (32 nm) trend without N-alkyl modification, while T-M shows red-shifted (26 nm) upon grinding. Moreover, the T-1 achieves blue-shifted MFC behaviors by amorphous states transition, and overcomes the limitations of conventionally ordered crystalline MFC materials. The phenomenons may be ascribable to mechano-induced short-range molecular order within the amorphous state. The powder X-ray diffraction, scanning electron microscopy, and differential scanning calorimetry analysis confirm amorphous states transition process. The T-1 and T-M reveal that partial reversible opposite MFC properties, AIE characteristic, and N-alkyl modification play a functional role in tuning their MFC behaviors and morphology structural changes.

We report the synthesis and characterization of four luminescent soft salts (S1–S4), composed of ion-paired cyclometalated Pt(II) complexes featuring either pyridine- or pyrimidine-based ligands. These compounds were prepared via metathesis reactions between complementary cationic and anionic Pt(II) precursors and were fully characterized by NMR spectroscopy and electrospray ionization high-resolution mass spectrometry. Their photophysical and chromic properties were investigated, and their excited states were modeled using time-dependent density functional theory. In DMSO solution, the emission originates from the anionic fragment, with quantum yields reaching up to 0.69. In the solid state, a redshifted emission is observed, attributed to metal–metal-to-ligand charge transfer excited states formed between paired complexes. Soft salts bearing a pyrimidine-based anionic fragment exhibit aggregation-induced emission, whereas their pyridine-based analogs show aggregation-caused quenching in DMSO/water mixtures. Soft salts incorporating pyrimidine-based ligands display vapochromic and acid-responsive behavior, with emission shifts or quenching upon exposure to solvent or acid vapors; partial reversibility is achieved through grinding or treatment with ammonia. These results underscore the tunability of photophysical properties through strategic azaheterocyclic ligand design and aggregation control.

Selective oxidation of α-hydroxy acids, particularly mandelic acids, is achieved by merging nickel and photoredox catalysis. This approach enables the discrete formation of aldehydes and ketones without observable overoxidation. By decoupling the decarboxylation and alcohol oxidation steps, the reaction proceeds under free-radical conditions with high efficiency. Mechanistic studies underscore the role of the nickel catalyst in facilitating these transformations. Additionally, this approach is extended to the decarboxylative oxidation of β-hydroxy acids and phenylglycines, generating carbonyl compounds upon hydrolysis. This method is scalable and holds the potential for broadening the scope of nickel-photoredox catalysis in oxidative processes.

The fundamental physics of the molecular excited state chirality refers to the breaking of time reversal symmetry of the electron density distribution in the excited states. Although steady-state circularly polarized luminescence (CPL) spectroscopy can measure the intensity difference between left- and right- circularly polarized emission, its time resolution limits the observation of excited state chirality generation and evolution, which accompany the excited state relaxation. It is envisaged that a combination of ultrafast time-resolved transient absorption and time-resolved circularly polarized luminescence (TRCPL) spectroscopy is a viable approach to achieve real-time observation of excited state chirality generation and evolution. In this concept, the technical principle and experimental setup of the recent developed femtosecond and nanosecond TRCPL spectroscopy instruments is presented. Additionally, examples are provided to showcase the utility of these techniques in the analysis of the excited state chirality origin and the mechanism of CPL enhancement by Föster resonance energy transfer.

Detecting dimethyl sulfoxide (DMSO) is important across chemical and environmental contexts because of its toxicity concerns and effects on cells. Fluorometry offers a rapid, sensitive readout, yet many dyes are scarce or synthetically complex. In this proof-of-concept study, we present a cheap and effective probe, namely 1,5-diisocyanonaphthalene (1,5-DIN), able to detect sulfoxides (dimethyl sulfoxide, DMSO and tetramethyl sulfoxide, TMSO) in various organic (MeCN, THF, MeOH, iPrOH, EtOAc) and aqueous media over the industrially and environmentally relevant range of 0.005–0.8 M (0.03-5% v/v). With a molecular weight of only 178.2 g mol⁻¹, this is the lowest molecular weight fluorescent probe for the purpose. The limit of detection (LOD) was 5 and 18 ppm for DMSO in MeCN and water, respectively. It was established that LOD values increase in protic solvents due to H-bond formation between the solvent and DMSO. Our detailed quantum chemical calculations revealed that upon photoexcitation the electron-deficient aromatic ring of DIN attracts DMSO, forming a stable complex. Quenching is explained by the proximity of the S₁ minimum to the T₁ triplet curve, allowing intersystem crossing and enabling a nonradiative de-excitation process through electron transfer from 1,5-DIN back to DMSO.

There is a pressing need to develop fluorescent dyes with light emission peaks in the wavelength range of 650–950 nm for optical live-cell imaging applications. The advancement of fluorescent dyes with a large Stokes shift is imperative for their biological applications. A novel domino reaction is developed with success for the synthesis of diverse 9aH-benzoquinolizines in 65–95% yields through reaction of α-silylaryl triflates, pyridine derivatives, and activated alkynes at room temperature. This single-flask reaction involves completion of a 1,2-elimination, a 1,2-addition, and an intermolecular (4 + 2) cycloaddition in situ. Among 15 new products, diethyl 9aH-tribenzo[c,f,h]quinolizine-1,2-dicarboxylate with extension of π-conjugation is identified as the top-performing dye. It shows near-infrared fluorescent emission at 674 nm with the Stokes shift of 197 nm, ε_max = 5.62 × 10⁴M^–1cm^–1, Φ_fl = 15.2%, and τ_av = 10.1 ns. It also exhibits excellent photostability with only 4.97% decomposed under irradiation with an Hg lamp for 60 min. With a remarkable 96 ± 2% viability, minimal toxicity toward CT-26 cancer cells, and coupled with promising results from confocal microscopy, this 9aH-tribenzoquinolizine emerges as an ideal fluorescent dye for imaging live cells.