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The unimolecular chemiluminescent decomposition of unsubstituted dioxetanone is analyzed at the complete active space self-consistent field level of theory combined with the multistate second-order multiconfigurational perturbation theory energy correction. The studies have shown that the vibrational distribution at the first conical intersection and the intersections among the states as the reaction proceeds between the two transition states are the origin of the population of the chemiluminescent states.

The visible and ultraviolet emission spectra of Y2O3:Er(super 3+) are interpreted as from Er(super 3+) situated at C2 sites. The optical spectra are remarkably complete and virtually free from vibronic structure, except for emission transitions to the two highest ground-state crystals field levels where the multiple structures are assigned to electron-phonon coupling effects.

The production of SO(N3)2 due to the reaction of AgN3 with SOCI2 is described. Evidence for this production is provided by photoelectron spectroscopy.

A four-step total synthesis of paeoveitol (1), a recently disclosed norditerpene natural product from Paeonia vetchii, is reported. This highly concise synthetic route was guided by biosynthetic considerations and enabled by an unusual intermolecular ortho-quinone methide [4 + 2]-cycloaddition reaction, which proceeded with excellent regio- and diastereoselectivity. Density functional theory (DFT) calculations point to a crucial intermolecular hydrogen bond and π-π stacking interaction that govern selectivity in this process. [ABSTRACT FROM AUTHOR]

CASSCF and CASPT2 studies on the reaction mechanism of the photochromic ring-opening process of a spiropyran (SP) (1',3',3'-trimethylspiro-[2H-1-benzopyran-2,2'-indoline], also known as BIPS) have been performed and possible excited-state C–O (and C–N) bond cleavage pathways and S1-to-S0 nonadiabatic transition channels have been explored. (1) The C–O bond dissociation in SP does not follow a conical-intersection mechanism that has been proposed in a model study with a simplified benzopyran. The CASSCF-optimized crossing points are actually avoided crossings with a large S1–S0 energy gap at the CASPT2 level; thus, they could not act as efficient S1-to-S0 funnels. (2) C–O bond cleavage paths on S1 leading to both the CCC (cis–cis–cis with respect to the configuration around α, β, γ) and TCC (trans–cis–cis) intermediates of merocyanine (MC) are barrierless, in line with the experimentally observed ultrafast formation of MC. (3) An unexpected low-energy hydrogen-out-of-plane (HOOP) valley on the (π→σ*) surface was located not far from the C-O bond cleavage path and was suggested to be an efficient S1-to-S0 nonadiabatic decay channel. Triggered by the active HOOP mode, the molecule can easily access the S1-HOOP valley and then make a transition to the S0 surface through the narrow S1-S0 gap that exists in an extended region. Nonadiabatic decay through a conical intersection on C-N dissociation path as well as the HOOP funnel is responsible for high internal conversion yields of SP. These findings shedding light on the complex mechanism of SP-MC interconversion provide fundamental information for design spiropyran-based photochromic devices. [ABSTRACT FROM AUTHOR]

The working mechanism of a geometrically overcrowded, chiral stilbene light-driven molecular rotary motor [(2R,2R)-2,2',7,7'-tetramethyl-1,1'-bis(indanylidene), 3] has been investigated by a potential energy surface (PES) study. The reaction paths of the two photoinitiated cis-trans (or E/Z) isomerization processes, namely, (P,P)-stable-cis→(M,M)-unstable-trans-3 and (P,P)-stable-trans→(M,M)-unstable-cis-3, have been explored at the CASPT2//CASSCF level of theory. The minimal energy reaction paths (MEPs) of these two processes are nearly parallel on the PESs, separated by a ridge of high inversion barrier. The MEPs have a remarkably steep slope, which drives C-C bond rotation unidirectionally. The asymmetric bias on the excited-state MEPs is caused by the substituents on the "fjord" region as well as by the phenyl moieties. The overall photoisomerization reaction can be described as a three-state (1B→2A→1A) multimode mechanism: The molecule excited to the 1B state first crosses one of the sloped 1B/2A seams, and then follows two cooperative torsional reaction modes to cross preferentially one of the two 2A/1A conical intersections to reach the isomerized ground-state product. [ABSTRACT FROM AUTHOR]

The photoluminescence features of Eu 3+-, Tb 3+-, Tb 3+/Eu 3+-alginate aerogel (hydrogel and alcogel) and Eu 3+-alginate xerogel hybrids were investigated. The Eu 3+-alginate aerogel and alcogel exhibit the highest 5D 0quantum efficiencies (9.9 and 8.2%, respectively), while the hydrogel and xerogel have lower values (5.2 and 5.6%, respectively). The Tb 3+/Eu 3+hybrids are multiwavelength emitters in which the emission color can be tuned across the chromaticity diagram from the red toward the yellowish-green spectral regions, crossing the white area by selecting the excitation wavelength. [ABSTRACT FROM AUTHOR]

Potential-energy surfaces for unimolecular decomposition of B(N3)3have been studied to understand the possible mechanism for BN generation. The decomposition of B(N3)3takes place on either the singlet and triplet surface, and both processes are high exothermic and obey sequential mechanisms. For the singlet reaction, the rate-determining step corresponds to cleavage of the first azide bond and linear 1NBNN instead of 1BN was suggested as the dominant product at room temperature. For the triplet surface, a fragment process from 3BN7to 3BN5is predicted to be the rate-determining step; once this barrier is counteracted, the subsequent decomposition processes could easily occur to form final product 3BN. In addition, the possible mechanism for generating BN film via B(N3)3was discussed based on MC−SCF calculation results. These findings might be helpful in understanding the controllable decomposition of B(N3)3as well as its application in generating BN films. [ABSTRACT FROM AUTHOR]

Density functional calculations have been carried out on a series of BCN hybrid fullerenes with certain substitution patterns in comparison with their parent compounds Cn (n = 30, 32, 36, 38, 40, 44, 48, 50, 52). The substitutional structures, energy gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, ionization potentials, electron affinities, as well as molecular electrostatic potentials have been systematically investigated. The following important points of BCN hybrid fullerenes are stressed:  The present studied fullerenes, comprising tubular “belt” and polar “cap”, could be divided into three types of structure; each has different indexes of tubular structure and terminal caps. The properties of BCN hybrid fullerenes depend on the type of “tubular belt + polar cap” structures, especially, the HOMO and LUMO characters and MEPs of BCN fullerene are strongly governed by their structure types. [ABSTRACT FROM AUTHOR]