The Journal of Physical Chemistry A最新文献

Phenothiazine-based donor-acceptor (D-A) molecules represent an important class of luminogens owing to their butterfly shaped geometry and rich excited-state behavior. Sulfur oxidation of the phenothiazine core has been widely employed as an effective strategy to tune their photophysical properties; however, the generality of this approach across different donor frameworks remains unclear. Herein, we report a systematic comparative study on the interplay between donor identity and sulfur oxidation in regulating the photophysics of phenothiazine-based D-A molecules. A carbazole-based molecular series with stepwise sulfur oxidation (CZ-S, CZ-SO, and CZ-SOO) was designed as a direct analogue of a previously reported diphenylamine-based system, enabling an unambiguous evaluation of donor-dependent effects under identical structural and oxidation conditions. Comprehensive photophysical investigations reveal that replacing diphenylamine with the more rigid carbazole donor fundamentally reshapes the impact of sulfur oxidation on emission behavior. In solution, carbazole-based derivatives exhibit attenuated solvatochromism and moderated intramolecular charge transfer (ICT), as confirmed by Lippert-Mataga analysis. In the aggregated and solid states, the carbazole system displays diversified emission behaviors, including aggregation-induced emission (AIE), aggregation-induced emission enhancement (AIEE), aggregation-caused quenching (ACQ), nonmonotonic solid-state emission shifts, and distinct mechanochromic mechanisms. Single-crystal X-ray diffraction analysis demonstrates that these donor-dependent photophysical differences originate primarily from enhanced conformational rigidity and restricted packing adaptability introduced by the carbazole donor, rather than from changes in intermolecular interaction motifs. This work establishes that sulfur oxidation alone does not universally dictate photophysical outcomes in phenothiazine-based systems; instead, donor identity plays a decisive and cooperative role. These findings provide new insights into the rational design of butterfly shaped luminogens with programmable photophysical responses.

This work investigates the gas-phase reactivity of fluorinated ethers CF₃CHFOCF₃ and CF₃CH₂OCF₃ toward ^•OH radicals, corresponding to the reactions CF₃CHFOCF₃ + ^•OH → CF₃C^•FOCF₃ + H₂O (1) and CF₃CH₂OCF₃ + ^•OH → CF₃C^•HOCF₃ + H₂O (2). Geometry optimizations and harmonic vibrational frequency calculations were performed at the M06-2X/6-311++G(3df,3pd) level of theory. More accurate energy estimates were obtained via single-point calculations using the CBS-QB3//M06-2X/6-311++G(3df,3pd) composite method. The potential energy profiles derived at 0 K indicate that, for both ethers, H-abstraction reactions proceed through transition states involving the formation of pre- and postreactive complexes. Rate constants were calculated over the temperature range of 200-1000 K employing canonical transition state theory (CTST), incorporating tunneling corrections via the Eckart method. The high-pressure limit Arrhenius equations derived at the CBS-QB3//M06-2X/6-311++G(3df,3pd) level can be represented by k = C exp[-(D₁ - (D₂/T))/T], where C = (5.9 ± 1.7) × 10^-12 cm³ molecule^-1 s^-1, D₁ = (4032 ± 1327) K, and D₂ = (4.7 ± 1.1) × 10⁵ K² for reaction (1), and C = (1.2 ± 0.2) × 10^-11 cm³ molecule^-1 s^-1, D₁ = (2921 ± 1168) K, and D₂ = (2.9 ± 0.8) × 10⁵ K² for reaction (2). Additionally, atmospheric lifetimes of the studied ethers were estimated and discussed.

We studied the X-ray-induced fragmentation of isothiocyanic acid, HNCS, following core ionization and excitation at the N1s, C1s, and S2p edges by Auger electron-ion coincidence spectroscopy. Mostly similar fragmentation products were identified at the different edges for normal and resonant Auger-Meitner decay, respectively. Upon normal Auger-Meitner decay, the dication was found to dissociate predominantly by C-S bond cleavage into HNC⁺ + S⁺ and CN⁺ + S⁺ ion pairs. The higher yield of undissociated HNCS²⁺ after S2p ionization is explained by a propensity for the population of low-binding energy final states at this edge. Following resonant core excitation into the 13a' or 4a″ orbital, S⁺ was found to be the main fragment, followed by HNC⁺. Fragments that require isomerization were observed with low yields after both core ionization and excitation. A comparison to isocyanic acid, HNCO, revealed significant differences in the fragmentation pattern of the two molecules.

C-H and C-D vibrations serve as versatile Raman probes for molecular detection and structural characterization, while site-specific vibrational analysis remains challenging due to overlapping modes and complex isotope effects. 1-Butanol (CH₃CH₂CH₂CH₂OH), a model small molecule with four distinct C-H moieties along its carbon chain, offers an ideal platform to decipher such complexity─yet the assignment of its gas-phase vibrational spectra (including Fermi resonances and site-dependent modes) has long been hindered by insufficient spectral resolution. Using a sensitive cavity-enhanced Raman instrument developed recently, we recorded high-resolution gas-phase Raman spectra of 1-butanol and two selectively deuterated isotopologues (CH₃CD₂CD₂CD₂OH and CD₃CD₂CD₂CH₂OH) in the ranges of 900-3100 cm^-1, covering both C-H/C-D bending and stretching regions. By integration of quantum chemical calculations, isotope substitution, and polarization-dependent measurements, the spectral ambiguities were unraveled. Our analysis enables the assignments of all major spectral features, elucidating the role of symmetric and antisymmetric stretching vibrations and Fermi-resonant modes at each C-H site along the 1-butanol carbon chain. A systematic comparison of C-H versus C-D vibrational patterns allows us to quantify isotope-induced shifts in frequency and intensity. These findings not only advance fundamental understanding of 1-butanol's vibrational landscape but also provide a robust framework for site-specific Raman analysis of complex organic molecules and guide the design of Raman-based imaging probes for biological and environmental applications.

Excited state intramolecular proton transfer (ESIPT) has been investigated in two prototypical systems─salicylaldehyde azine (SAA) and 1,5-dihydroxyanthraquinone (DHAQ)─using transient absorption spectroscopy upon ultraviolet excitation into the less studied higher excited (S_n) manifold. Excitation with sub-30 fs pulses and broadband visible probing has allowed for direct measurement of the ESIPT rate. In conjunction with steady-state measurements and TD-DFT calculations, a complete delineation of the ultrafast photophysics has been carried out. In SAA, ESIPT remains ultrafast (∼30 fs), consistent with previous S₁ excitation studies. Coherent vibrational beats maps reveal significant wavelength dependence, however. Theoretical analysis suggests that the observed modes and their intensities in coherent vibrational spectra are modulated by the nature of the electronically excited state. In DHAQ, the first direct observation of ESIPT presents a time-constant of ∼85 fs, and a slower component of 9 ps, akin to previous reports on double-proton transfer systems. Collectively, the results suggest that while the ultrafast ESIPT rate remains largely invariant vis-à-vis the excitation energy, the product yield, as well as accompanying coherent oscillations, may be substantively altered, owing to the existence of alternative decay pathways.

We present the first quantum computing simulation of wavepacket dynamics in an HO₂-water cluster. These systems are of great interest in atmospheric chemistry and, due to anharmonicity, can display multidimensional quantum nuclear effects arising from delocalized hydrogen bond networks. Here, we utilize the Quantum Shannon Decomposition (QSD) method to represent a quantum propagator for the nuclear degrees of freedom of the HO₂ radical interacting with one and two water molecules, in the presence of an electronic potential energy surface, and in terms of the R_y, R_z, and CNOT quantum gates. The resultant time evolution of the quantum wavepacket, constructed by using the Qiskit quantum simulation tool, with a Python driver, yields a vibrational spectrum that is in very good agreement with the classically obtained result. The numerical demonstration here is restricted to one- and two-nuclear dimensions and hence is a proof of principle, but future implementations will include novel tensor network strategies to reduce quantum circuit depth and expand to higher dimensions.

Dynamic excimer formation in solution-phase π-conjugated systems presents a promising route toward tunable photophysical properties, yet precise control over these transient species remains limited. Herein, a series of bisphenalenyl derivatives is shown to exhibit excimer emission that is modulated through strategic tailoring of side chains (ethylphenyl, n-butylphenyl, and n-hexyl). Two phenyl-substituted derivatives exhibit reversible, concentration-dependent excimer emission consistent with excited-state dimerization. In contrast, an aliphatically substituted bisphenalenyl moiety displays exclusively monomeric emission. Steady-state and time-resolved spectroscopy, time-dependent density functional theory, and diffusion-ordered NMR spectroscopy are employed to confirm that excimer formation arises due to excited-state encounters, with no evidence of ground-state aggregation in acetonitrile. However, diffusion-ordered NMR spectroscopy data reveal dimer formation in tetrachloroethane. Notably, the introduction of substoichiometric molar ratios of HBF₄ induces excimer emission at even lower concentrations of the bisphenalenyl moiety, demonstrating a route to stimulus-responsive control. These results provide a structure-environment framework for modulating dynamic excimer formation in charged π-systems and inform the rational design of responsive fluorescent materials.

We discuss the computation of partial Auger decay widths with equation-of-motion ionization-potential coupled-cluster (EOMIP-CCSD) theory in the framework of non-Hermitian quantum mechanics (NHQM). In NHQM, the decaying character of metastable states is described with complex energies and the total decay width is obtained directly from the total energy. In contrast, the computation of partial decay widths, i.e., the contributions of different decay channels to the total width, requires further analysis. However, partial widths are important for Auger spectroscopy as they determine the probability with which different final states are formed and hence the shape of the Auger spectrum. Recently, we introduced Auger channel projectors (ACPs), which selectively remove decay channels from the EOMIP-CCSD excitation manifold. This method requires a separate EOMIP-CCSD calculation for each decay channel. Here, we suggest an alternative: We solve the EOMIP-CCSD equations for the core-ionized state in the full excitation manifold and decompose the imaginary part of the resulting energy. In this way, we obtain all partial decay widths at once. We compute Auger spectra for K-edge-ionized states of methane, ethane, and hydrogen sulfide, and a Coster–Kronig spectrum for L₁-edge-ionized hydrogen sulfide. The results obtained with our new approach differ only negligibly from ACP results. We also present the first Auger spectra for the cyanide anion, including vibrational broadening, and discuss the differences between the spectra of the carbon core hole and the nitrogen core hole.