Chiral Teropyrenes: Synthesis, Structure, and Spectroscopic Studies.

We present the inaugural synthesis of a chiral teropyrene achieved through a four-fold alkyne benzannulation catalyzed by InCl3, resulting in good yields. The product underwent thorough characterization using FT-Raman and FT-IR spectroscopies, demonstrating a close agreement with calculated spectra. X-ray crystallographic analysis unveiled a notable twist in the molecule's backbone, with an end-to-end twist angle of 51°, consistent with computational predictions. Experimentally determined enantiomeric inversion barriers revealed a significant energy barrier of 23 kcal/mol, facilitating the isolation of enantiomers for analysis via circular dichroism (CD) and circularly polarized luminescence (CPL) spectroscopies. These findings mark significant strides in the synthesis and characterization of chiral teropyrenes, offering insights into their structural and spectroscopic properties.

Nanographene-Based Decoration as a Panchromatic Antenna for Metalloporphyrin Conjugates.

Porphyrins, a type of heterocyclic aromatic compounds consisting of tetrapyrroles connected by four substituted methine groups, are appealing building blocks for solar energy applications. However, their photosensitization capability is limited by their large optical energy gap, which results in a mismatch in absorption toward efficient harvesting of the solar spectrum. Porphyrin π-extension by edge-fusing with nanographenes can be employed for narrowing their optical energy gap from 2.35 to 1.08 eV, enabling the development of porphyrin-based panchromatic dyes with an optimized energy onset for solar energy conversion in dye-sensitized solar fuel and solar cell configurations. By combining time-dependent density functional theory with fs transient absorption spectroscopy, it is found that the primary singlets, which are delocalized across the entire aromatic part, are transferred into metal centred triplets in only 1.2 ps; and subsequently, relax toward ligand-delocalized triplets. This observation implies that the decoration of the porphyrin moiety with nanographenes, while having a large impact on the absorption onset of the novel dye, promotes the formation of a ligand-centred lowest triplet state of large spatial extension, potentially interesting for boosting interactions with electron scavengers. These results reveal a design strategy for broadening the applicability of porphyrin-based dyes in optoelectronics.

Zigzag-Edged Polycyclic Aromatic Hydrocarbons from Benzo[m]tetraphene Precursors.

A series of zigzag-edged polycyclic aromatic hydrocarbons (PAHs) (Z1-Z3) were synthesized from 2,12-dibromo-7,14-diphenyl-benzo[m]tetraphene (9) as a versatile building block. Their structures were unambiguously confirmed by laser desorption/ionization time-of-flight mass spectrometry, 1 H NMR, Raman, and Fourier-transformed infrared (FTIR) spectroscopies as well as scanning tunneling microscopy. The fingerprint vibrational modes were elucidated with theoretical support. The edge- and size-dependent optical properties were characterized by UV-Vis absorption and fluorescence spectroscopy and DFT calculations. Moreover, ultrafast transient absorption spectroscopy revealed distinct modulation of the photophysical properties upon π-extension from Z1 to Z2, the latter having a gulf edge.

Insights into the phototautomerism of free-base 5, 10, 15, 20-tetrakis(4-sulfonatophenyl) porphyrin.

Phototautomerism in the excited states of free-base 5, 10, 15, 20-tetrakis(4-sulfonatophenyl) porphyrin (H2TPPS4-) has been investigated combining, for the first time, advanced Electron Paramagnetic Resonance (EPR) with fluorescence and Raman spectroscopy. Triplet EPR spectroscopy, performed in protic and deuterated solvents and in the presence of photoselection, confirms the occurrence of phototautomerization and additionally suggests the formation of the cis tautomer as a minor component. The zero-field splitting parameters and triplet sublevel populations indicate that the process is slow in the triplet state. The results obtained by EPR combined with photoselection and fluorescence anisotropy have been interpreted within a model which accounts for a fast trans-trans tautomerization promoted by a spin-vibronic coupling mechanism for intersystem crossing, with an even distribution of the two trans tautomers at liquid nitrogen temperatures for H2TPPS4-.

SERS Detection of the Anti-Epileptic Drug Perampanel in Human Saliva.

Surface-Enhanced Raman Scattering (SERS) can obtain the spectroscopic response of specific analytes. In controlled conditions, it is a powerful quantitative technique. However, often the sample and its SERS spectrum are complex. Pharmaceutical compounds in human biofluids with strong interfering signals from proteins and other biomolecules are a typical example. Among the techniques for drug dosage, SERS was reported to detect low drug concentrations, with analytical capability comparable to that of the assessed High-Performance Liquid Chromatography. Here, for the first time, we report the use of SERS for Therapeutic Drug Monitoring of the Anti-Epileptic Drug Perampanel (PER) in human saliva. We used inert substrates decorated with gold NPs deposited via Pulsed Laser Deposition as SERS sensors. We show that it is possible to detect PER in saliva via SERS after an optimized treatment of the saliva sample. Using a phase separation process, it is possible to extract all the diluted PER in saliva from the saliva phase to a chloroform phase. This allows us to detect PER in the saliva at initial concentrations of the order of 10-7 M, thus approaching those of clinical interest.

Investigating Perampanel Antiepileptic Drug by DFT Calculations and SERS with Custom Spinning Cell.

SERS, a clinical practice where medical doctors can monitor the drug concentration in biological fluids, has been proposed as a viable approach to therapeutic drug monitoring (TDM) of the antiepileptic drug Perampanel. The adoption of an acidic environment during the SERS experiments was found to be effective in enhancing the spectroscopic signal. In this work, we combine SERS experiments, conducted with a custom spinning cell in controlled acidic conditions, with DFT calculations aimed at investigating the possible protonated forms of Perampanel. The DFT-simulated Raman spectra of protonated Perampanel accounts for most of the observed SERS signals, thus explaining the effective role of protonation of the analyte. Our results suggest protonation as a viable approach to fostering SERS of alkaline drugs.

Pushing Up the Size Limit of Boron-doped peri-Acenes: Modular Synthesis and Characterizations.

Heteroatom-doped peri-acenes (PAs) have recently attracted considerable attention considering their fascinating physical properties and chemical stability. However, the precise sole addition of boron atoms along the zigzag edges of PAs remains challenging, primarily due to the limited synthetic approach. Herein, we present a novel one-pot modular synthetic strategy toward unprecedented boron-doped PAs (B-PAs), including B-[4,2]PA (1 a-2), B-[4,3]PA (1 b-2) and B-[7,2]PA (1 c-3) derivatives, through efficient intramolecular electrophilic borylation. Their chemical structures are unequivocally confirmed with a combination of mass spectrometry, NMR, and single-crystal X-ray diffraction analysis. Notably, 1 b-2 exhibits an almost planar geometry, whereas 1 a-2 displays a distinctive bowl-like distortion. Furthermore, the optoelectronic properties of this series of B-PAs are thoroughly investigated by UV/Vis absorption and fluorescence spectroscopy combined with DFT calculation. Compared with their parent all-carbon analogs, the obtained B-PAs exhibit high stability, wide energy gaps, and high photoluminescence quantum yields of up to 84 %. This study reveals the exceptional ability of boron doping to finely tune the physicochemical properties of PAs, showcasing their potential applications in optoelectronics.

Bottom-up Solution Synthesis of Graphene Nanoribbons with Precisely Engineered Nanopores.

The incorporation of nanopores into graphene nanostructures has been demonstrated as an efficient tool in tuning their band gaps and electronic structures. However, precisely embedding the uniform nanopores into graphene nanoribbons (GNRs) at the atomic level remains underdeveloped especially for in-solution synthesis due to the lack of efficient synthetic strategies. Herein we report the first case of solution-synthesized porous GNR (pGNR) with a fully conjugated backbone via the efficient Scholl reaction of tailor-made polyphenylene precursor (P1) bearing pre-installed hexagonal nanopores. The resultant pGNR features periodic subnanometer pores with a uniform diameter of 0.6 nm and an adjacent-pores-distance of 1.7 nm. To solidify our design strategy, two porous model compounds (1 a, 1 b) containing the same pore size as the shortcuts of pGNR, are successfully synthesized. The chemical structure and photophysical properties of pGNR are investigated by various spectroscopic analyses. Notably, the embedded periodic nanopores largely reduce the π-conjugation degree and alleviate the inter-ribbon π-π interactions, compared to the nonporous GNRs with similar widths, affording pGNR with a notably enlarged band gap and enhanced liquid-phase processability.

Cove-Edged Graphene Nanoribbons with Incorporation of Periodic Zigzag-Edge Segments.

Structurally precision graphene nanoribbons (GNRs) are promising candidates for next-generation nanoelectronics due to their intriguing and tunable electronic structures. GNRs with hybrid edge structures often confer them unique geometries associated with exotic physicochemical properties. Herein, a novel type of cove-edged GNRs with periodic short zigzag-edge segments is demonstrated. The bandgap of this GNR family can be tuned using an interplay between the length of the zigzag segments and the distance of two adjacent cove units along the opposite edges, which can be converted from semiconducting to nearly metallic. A family member with periodic cove-zigzag edges based on N = 6 zigzag-edged GNR, namely 6-CZGNR-(2,1), is successfully synthesized in solution through the Scholl reaction of a unique snakelike polymer precursor (10) that is achieved by the Yamamoto coupling of a structurally flexible S-shaped phenanthrene-based monomer (1). The efficiency of cyclodehydrogenation of polymer 10 toward 6-CZGNR-(2,1) is validated by FT-IR, Raman, and UV-vis spectroscopies, as well as by the study of two representative model compounds (2 and 3). Remarkably, the resultant 6-CZGNR-(2,1) exhibits an extended and broad absorption in the near-infrared region with a record narrow optical bandgap of 0.99 eV among the reported solution-synthesized GNRs. Moreover, 6-CZGNR-(2,1) exhibits a high macroscopic carrier mobility of ∼20 cm2 V-1 s-1 determined by terahertz spectroscopy, primarily due to the intrinsically small effective mass (m*e = m*h = 0.17 m0), rendering this GNR a promising candidate for nanoelectronics.

The Effects of Ring Strain on Cyclic Tetraaryl[5]cumulenes.

Cyclic tetraaryl[5]cumulenes (1 a-f) have been synthesized and studied as a function of increasing ring strain. The magnitude of ring strain is approximated by the extent of bending of the cumulenic core as assessed by a combination of X-ray crystallographic analysis and DFT calculations. Trends are observed in 13 C NMR, UV-vis, and Raman spectra associated with ring strain, but the effects are small. In particular, the experimental HOMO-LUMO gap is not appreciably affected by bending of the [5]cumulene framework from ca. 174° (λmax =504 nm) in 1 a to ca. 178° (λmax =494 nm) in 1 f.

UV resonance Raman spectroscopy of weakly hydrogen-bonded water in the liquid phase and on ice and snow surfaces.

The hydrogen bond network has a major role in determining the physical and chemical properties of water both in the solid and in the liquid state. In the bulk liquid phase, there is a coexistence of water molecules with different degrees of coordination and their relative amount changes according to the conditions (e.g., temperature, presence of solutes). Ice shows a larger amount of topologically under-coordinated water molecules at the surface as compared to the bulk. Snow is composed of many ice crystallites, and it differs from bulk ice because of the much larger specific surface area. The OH-stretching band is the most intense signal of the Raman spectrum of water, and it gives direct insight about the hydrogen bond network. In this work we compared the OH-stretching region of the Raman spectra of water, ice and snow acquired with excitations in the visible (532 nm) and in the UV-C range (250-200 nm) by exploiting the tunability of the synchrotron radiation. By moving towards the highest energy excitation we observed in liquid water a monotonic increase of the relative intensities of the peaks associated with weakly hydrogen-bonded water molecules. With visible excitation, the Raman spectrum of snow displays a larger contribution from weakly hydrogen-bonded water molecules at the surfaces when compared to the spectrum of bulk ice. By using excitation sources in the UV-C range, we observe a further enhancement of the contribution of the surfaces in the spectra of snow. By considering the reported changes of the water absorption coefficient in relation to the hydrogen bonding environment, we interpreted our results as a preferential pre-resonance excitation of weakly hydrogen-bonded water molecules induced by the UV-C sources.

Unsymmetrical benzothiazole-based dithienylethene photoswitches.

Herein, we investigate the structure-property relationships in a new series of benzothiazole based unsymmetrical hexafluorocyclopentene dithienylethenes (DTEs) and compare the results with the known facts for symmetric diarylethenes (DAEs). We reveal high photocyclization efficiency resulting from a significant shift of ground state equilibrium to the antiparallel conformation and a barrierless excited state pathway to conical intersection, which remains unperturbed even in polar solvents for most of the prepared DTEs. Furthermore, we uncover that the rate of back thermal cycloreversion correlates clearly more with the central C-C bond-length in the transition state than with the central C-C bond-length in the ground state of the cyclic form. Finally, our detailed vibrational spectral analysis of studied DTEs points out significant changes in Raman and infrared spectra during photoswitching cycles which pave the way for a non-destructive readout of stored information.

Raman Spectroscopy-Based Assessment of the Liquid Water Content in Snow.

In snow, water coexists in solid, liquid and vapor states. The relative abundance of the three phases drives snow grain metamorphism and affects the physical properties of the snowpack. Knowledge of the content of the liquid phase in snow is critical to estimate the snowmelt runoff and to forecast the release of wet avalanches. Liquid water does not spread homogeneously through a snowpack because different snow layers have different permeabilities; therefore, it is important to track sudden changes in the amount of liquid water within a specific layer. We reproduced water percolation in the laboratory, and used Raman spectroscopy to detect the presence of the liquid phase in controlled snow samples. We performed experiments on both fine- and coarse-grained snow. The obtained snow spectra are well fitted by a linear combination of the spectra typical of liquid water and ice. We progressively charged snow with liquid water from dry snow up to soaked snow. As a result, we exploited continuous, qualitative monitoring of the evolution of the liquid water content as reflected by the fitting coefficient c.

Pyrrole-Embedded Linear and Helical Graphene Nanoribbons.

Linear and helical graphene nanoribbons (L-PyGNR and H-PyGNR) bearing electron-rich pyrrole units have been synthesized by using the photochemical cyclodehydrochlorination (CDHC) reaction. The pyrrole units in the polymer backbone make the polymer electron-rich with moderate bandgap values and relatively high HOMO energy levels. The planarization of the pyrrole unit through cyclization yields a bandgap value almost 0.5 eV lower than that measured for polypyrrole. Conductivity values in the thin film up to 0.12 S/cm were measured for the chemically oxidized L-PyGNR (four-point method). Both GNRs showed excellent fluorescence sensing properties for TNT in solution with KSV values up to 6.4 × 106 M-1.

A Bioorthogonal Probe for Multiscale Imaging by 19F-MRI and Raman Microscopy: From Whole Body to Single Cells.

Molecular imaging techniques are essential tools for better investigating biological processes and detecting disease biomarkers with improvement of both diagnosis and therapy monitoring. Often, a single imaging technique is not sufficient to obtain comprehensive information at different levels. Multimodal diagnostic probes are key tools to enable imaging across multiple scales. The direct registration of in vivo imaging markers with ex vivo imaging at the cellular level with a single probe is still challenging. Fluorinated (19F) probes have been increasingly showing promising potentialities for in vivo cell tracking by 19F-MRI. Here we present the unique features of a bioorthogonal 19F-probe that enables direct signal correlation of MRI with Raman imaging. In particular, we reveal the ability of PERFECTA, a superfluorinated molecule, to exhibit a remarkable intense Raman signal distinct from cell and tissue fingerprints. Therefore, PERFECTA combines in a single molecule excellent characteristics for both macroscopic in vivo 19F-MRI, across the whole body, and microscopic imaging at tissue and cellular levels by Raman imaging.

Structural and Spectroscopic Properties of Benzoylpyridine-Based Hydrazones.

Photochromic hydrazones are attracting the attention in the field of photochromic systems especially due to their P-type character. To understand the structural features and their correlation with the spectroscopic data, UV-Vis, vibrational and ellipsometry spectroscopic techniques are employed with the support of density functional theory (DFT) calculations to three hydrazone derivatives based on benzoylpyridine. Interestingly, analysis of the structure shows the presence of two distinct rotamers around the pyridine ring with different energy and the well-defined conjugation path that changes due to E to Z isomerization especially in the hydrazone -C=N-NH part of the skeleton. IR and Raman spectra are analyzed, showing a higher selectivity in the Z form; moreover, the comparison with the normal modes proves the effect of the reaction on the backbone structure. The experimental results are in good agreement with the theoretical predictions, especially in the case of the Raman spectrum. The molecular polarization also changes from E to Z forms as predicted by DFT calculations. Spectroscopic ellipsometry on thin films of TOPAS doped with 10 %wt of the dimethylamino hydrazone derivative is used to prove such change at the molecular level. A modulation of the refractive index is observed, and it is correlated with the concentration of the active moiety and the calculated electronic polarizabilities.

Sensing the Anti-Epileptic Drug Perampanel with Paper-Based Spinning SERS Substrates.

The applications of SERS in therapeutic drug monitoring, or other fields of analytical chemistry, require the availability of sensitive sensors and experimental approaches that can be implemented in affordable ways. In this contribution, we show the production of cost-effective SERS sensors obtained by depositing Lee-Meisel Ag colloids on filter paper either by natural sedimentation or centrifugation. We have characterized the morphological and plasmonic features of the sensors by optical microscopy, SEM, and UV-Vis spectroscopy. Such sensors can be used to quantify by SERS the anti-epileptic drug Perampanel (in the concentration range 1 × 10-4-5 × 10-6 M) by spinning them during the micro-Raman measurements on the top of a custom device obtained from spare part hard disk drives. This approach minimizes laser-induced heating effects and allows averaging over the spatial non-uniformity of the sensor.

Persistent peri-Heptacene: Synthesis and In Situ Characterization.

n-peri-Acenes (n-PAs) have gained interest as model systems of zigzag-edged graphene nanoribbons for potential applications in nanoelectronics and spintronics. However, the synthesis of n-PAs larger than peri-tetracene remains challenging because of their intrinsic open-shell character and high reactivity. Presented here is the synthesis of a hitherto unknown n-PA, that is, peri-heptacene (7-PA), in which the reactive zigzag edges are kinetically protected with eight 4-tBu-C6 H4 groups. The formation of 7-PA is validated by high-resolution mass spectrometry and in situ FT-Raman spectroscopy. 7-PA displays a narrow optical energy gap of 1.01 eV and exhibits persistent stability (t1/2 ≈25 min) under inert conditions. Moreover, electron-spin resonance measurements and theoretical studies reveal that 7-PA exhibits an open-shell feature and a significant tetraradical character. This strategy could be considered a modular approach for the construction of next-generation (3 N+1)-PAs (where N≥3).

Electric-Field-Induced Effects on the Dipole Moment and Vibrational Modes of the Centrosymmetric Indigo Molecule.

Intense static electric fields can strongly perturb chemical bonds and induce frequency shifts of the molecular vibrations in the so-called vibrational Stark effect. Based on a density functional theory (DFT) approach, here, we report a detailed investigation of the influence of oriented external electric fields (OEEFs) on the dipole moment and infrared (IR) spectrum of the nonpolar centrosymmetric indigo molecule. When an OEEF as intense as ∼0.1 V Å-1 is applied, several modifications in the IR spectrum are observed. Besides the notable frequency shift of some modes, we observe the onset of new bands-forbidden by the selection rules in the zero-field case. Such a neat field-induced modification of the vibrational selection rules, and the subsequent variations of the peaks' intensities in the IR spectrum, paves the way toward the design of smart tools employing centrosymmetric molecules as proxies for mapping local electric fields. In fact, here, we show that the ratio between the IR and the Raman intensities of selected modes is proportional to the square of the local field. This indicator can be used to quantitatively measure local fields, not only in condensed matter systems under standard conditions but also in field-emitting-tip apparatus.

Synthesis of Natural-Like Snow by Ultrasonic Nebulization of Water: Morphology and Raman Characterization.

The current devices used to produce massive amounts of snow (i.e., snow machines) can be improved with concern to both the energy efficiency and the quality of snow. Here we investigate an alternative snow production method based on the ultrasonic nebulization of water and its subsequent condensation on the cold surfaces of a refrigerator. Inspection of the snow samples with a stereo optical microscope shows both dendritic and granular snow morphologies. The characterization of the samples by Raman spectroscopy shows a behavior consistent with that of a natural, low-density snow. Our results indicate that ultrasonic nebulization of water is an effective strategy for producing natural-like snow at the laboratory scale.