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The initial nonadiabatic decay dynamics of E,E-2,4-hexadienal (HAL) in the light absorbing S2(ππ*) state were studied using resonance Raman spectroscopy and complete-active space self-consistent field (CASSCF) calculations. The UV and vibrational spectra were assigned on the basis of the UV absorption, Fourier transform (FT)-Raman and FT-infrared measurements, the density-functional theory computations, and the normal mode analysis. The A-band resonance Raman spectra in cyclohexane and acetonitrile were obtained at 282.4, 273.9, 266.0, 252.7, and 245.9 nm excitation wavelengths, respectively, to probe the corresponding structural dynamics of HAL. The A-band absorption cross section and the corresponding absolute resonance Raman cross sections were simulated using a simple model based on the time-dependent wave-packet theory in a Brownian oscillator model. The geometric structures of the singlet electronic excited states and their curve-crossing points were optimized at the CASSCF level of theory. The obtained short-time structural dynamics in easy-to-visualize internal coordinates were then compared with the CASSCF-predicted structural-parameter changes of S2(ππ*)S1(nπ*)-n (n = 1–4). Our results indicate that the initial population of HAL in the S2 state ramifies in or nearby the Franck–Condon (FC) region, leading to five S2(ππ*) → S1(nπ*) internal conversion pathways due to the flexibility of the molecular chain and the different electronic resonant structures formed nearby FC of the S2 state. Then, the formed S1 transient species, which have different geometric structures and different energy partitions, undergo different photophysical processes, such as S1 → S0 internal conversion, S1 → T1 intersystem crossing, and the S1 → S′1 photoisomerization reaction. The substitution effect on the S2(ππ*) → S1(nπ*) internal conversion dynamics and the trans–cis photoisomerization reaction is proposed in terms of the p-π conjugation interaction or the p-σ superconjugation interaction. [ABSTRACT FROM AUTHOR]

Abstract: Edible mushrooms are widely usedtoday but the heavy metal pollution of edible mushrooms is not conducive to its industrialization. A novel chloromethylated polystyrene-g-2-adenine chelating resin (AR resin) with simple [...]

The structures, sizes, reactivities, clusters, and other properties of materials in the microsolvation environment are currently attracting the interest of scientists in materials science and chemical biology. In this study, we investigated the structures of 4-methyl-1,2,4-triazole-3-thione (4MTT) in various environments, including solid, protic, and aprotic solvents. Fourier transform infrared and Raman spectroscopy, and density functional theory calculations were used to assign the vibrational spectra of the 4MTT crystals and microsolvated hydrogen bonding clusters in acetonitrile, water, and methanol. In addition, the ultraviolet-visible (UV-vis) absorption spectra of the microsolvated hydrogen bonding clusters were simulated using time-dependent density functional theory. The UV-vis absorption and Raman spectra of 4MTT results showed that solvent polarity and hydrogen bonding contributed to the observed spectral band shifts in different solvents. The hydrogen-bond networks were centered on the electronegative groups, and the microsolvation clusters were further classified as 4MTT(solvent)n clusters: for n = 1 in acetonitrile and n = 2 in water and methanol. Afterward, nanosecond transient absorption spectroscopy was used to investigate the excited state dynamics in solvents; it was also used in conjunction with complete active space self-consistent field calculations to characterize the excited-state decay mechanism and the formation of long-term triplet species. [ABSTRACT FROM AUTHOR]

An ab initio study of the structures, conformational stabilities and vibrational frequencies of a number of halogenated ethyl radicals is presented. It is suggested that it is important to take account of electron correlation effects for the bromoethyl radicals.