In this review we present a structured overview of the chemical catalytic systems containing any component derived from natural product for cycloaddition carbon dioxide to epoxides form cyclic carbonates.

Ultrafast decay processes detected after absorption of UV radiation in gas-phase pyrimidine nucleobases uracil, thymine, and cytosine are ascribed to the barrierless character pathway along low-lying 1(ππ*) hypersurface connecting Franck−Condon region with an out-of-plane distorted ethene-like conical intersection ground state. Longer lifetime decays low quantum yield emission on other hand related presence a state planar minimum S1 surface barriers access intersections. A unified model for...

The mechanism of the photoisomerisation azobenzene has been studied by means multiconfigurational ab initio calculations. Our results show that it is necessary to account for dynamic electron correlation in location critical points (CASPT2 optimizations) obtain a correct description topography potential energy surfaces low singlet excited states. By using this methodology, we have found state populated initial excitation S2 (ππ*) state, which decays very efficiently S1 (nπ*) at pedal-like...

In electron donor/acceptor species such as 4-(dimethylamino)benzonitrile (DMABN), the excitation to S2 state is followed by internal conversion locally excited (LE) state. Dual fluorescence then becomes possible from both LE and twisted intramolecular charge-transfer (TICT) states. A detailed mechanism for ICT of DMABN 4-aminobenzonitrile (ABN) presented in this work. The two emitting S1 are adiabatically linked along amino torsion reaction coordinate. However, S2/S1 CT-LE radiationless...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTExcited-State Potential Surface Crossings in Acrolein: A Model for Understanding the Photochemistry and Photophysics of .alpha.,.beta.-EnonesMar Reguero, Massimo Olivucci, Fernando Bernardi, Michael A. RobbCite this: J. Am. Chem. Soc. 1994, 116, 5, 2103–2114Publication Date (Print):March 1, 1994Publication History Published online1 May 2002Published inissue 1 March 1994https://doi.org/10.1021/ja00084a056RIGHTS & PERMISSIONSArticle...

Abstract Catalytic carbon dioxide transformation to low valence molecules such as monoxide, formic acid, methanol and methane is a sustainable way produce fuels chemicals. Molecular catalysts can be designed selectively transform CO 2 at mild conditions, but solvent medium required. Instead, the molecular immobilized on solid supports facilitate continuous flow procedure separation of products recycle catalytic systems for more process. Photosensitive may also favor light‐absorbing steps...

Ab initio calculations including correlation energy are reported on a series of halogen-substituted carbenes and silylenes: CH2, CHF, CF2, CHCl, CCl2, CHBr, CBr2, SiH2, SiHF, SiF2, using the difference-dedicated configuration interaction method. All these compounds with exception CH2 have singlet ground states. The singlet-triplet differences in very good agreement experiment when available, as well other high level calculations. separation is also determined trifluoromethyl carbenes, CHCF3,...

By integrating the results of MS-CASPT2/CASSCF and TD-PBE0 calculations, we propose a mechanism for decay excited dark state in pyrimidine, fully consistent with all available experimental results. An effective conical intersection (CI-nπ) exists between spectroscopic π/π* (Sπ) n/π* (Sn), fraction population decays to minimum Sn (Sn-min). The ground-state is not involved mechanism, because its high energy gap respect Sn-min. On other hand, especially hydrogen bonding solvents, Sn-min CI-nπ...

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTChemiluminescent decomposition of 1,2-dioxetanes: an MC-SCF/MP2 study with VB analysisMar Reguero, Fernando Bernardi, Andrea Bottoni, Massimo Olivucci, and Michael A. RobbCite this: J. Am. Chem. Soc. 1991, 113, 5, 1566–1572Publication Date (Print):February 1, 1991Publication History Published online1 May 2002Published inissue 1 February 1991https://pubs.acs.org/doi/10.1021/ja00005a018https://doi.org/10.1021/ja00005a018research-articleACS...

Abstract To stop the global warming, a complementary alternative to decrease of CO 2 production is reduction its amount in atmosphere by capture and transformation into consumer products. One most interesting primary products CO, used synthesise liquid fuels. Perhaps attractive way reducing photocatalytic route. know details mechanism this reaction can help design more efficient catalytic systems. In review, we compile studies, undertaken from both computational experimental approaches,...

A mechanism of the thermal and photochemical bleaching merocyanine to spiropyran is proposed on basis CASSCF/CASPT2 calculations 6-(2-propenyliden)cyclohexadienone model system. Our results suggest that this transformation takes place in two steps. First, initially pumped 1(pi-pi) S2 undergoes radiationless decay 1(n-pi) S1 via an extended S2/S1 conical intersection seam runs approximately parallel trans-to-cis isomerization coordinate, a few kilocalories per mole higher energy. Thus, -->...

A study combining accurate quantum chemistry and full-dimensional dynamics is presented to confirm the existence of an ultrafast radiationless decay channel from charge-transfer state locally excited in 4-aminobenzonitrile. This intramolecular pathway proceeds through a newly found planar conical intersection, it shown be more efficient presence acetonitrile than gas phase. Our results are consistent with recent experimental observations.

The dual fluorescence of 4-(dimethylamino)benzonitrile (DMABN) has been intensively studied in the last decades, but surprisingly there is not any detailed theoretical study its photochemistry polar solvents. In this work, we rationalize different luminescent behavior 4-aminobenzonitrile (ABN) and DMABN acetonitrile by a computational developed at CASSCF/CASPT2 level using Polarized Continuum Model to reproduce solvent environment. We present here critical geometries, energies, connections...

Zinc(II) complexes [Zn(L1-L5)Cl2] with tetra-aza donor ligands bearing phenanthroline and bipyridine bis(aniline) skeleton L1-L5 have been prepared characterised. These were selected to analyse the influence on catalytic activity for CO2-cycloaddition epoxides of three parameters: steric hindrance orto substituent aniline ring, central nature non-aromatic amine. X-ray diffraction characterisation [Zn(L1)Cl2] [Zn(L2)Cl2] showed that geometry is pentacoordinate while in case [Zn(L5)Cl2] a...

The simplicity of the fluorescence pattern ABN is in fact outcome an intricate interplay between locally excited and charge transfer states.

There is still controversy about the structure of intramolecular charge transfer (ICT) emitting species in pi-electron donor-acceptor systems that show dual fluorescence. Although twisted ICT model quite generally accepted, planar not ruled out because firm experimental evidence supports it. Among these it fact some rigidized such as bicyclic 4-aminobenzonitrile derivatives exhibit We present here an ab initio CASSCF/CASPT2 study a series compounds with alicyclic chain ranging from 5 to 7...

Ab initio calculations show that a possible mechanism for the photomagnetism in copper octacyanomolybdate compounds consists of initial excitation diamagnetic Cu(II)-Mo(IV-CS) pair to Cu(II)-Mo(IV-T) state, whose geometry relaxation stabilizes magnetic doublet and quartet states.

Azo compounds are organic photochromic systems that have the possibility of switching between cis and trans isomers under irradiation. The different photochemical properties these make azo into good light-triggered switches, their significantly geometries them very interesting as components in molecular engines or mechanical switches. For instance, ligands used coordination complexes to trigger photoresponsive properties. light-induced trans-to-cis isomerization phenylazopyridine (PAPy)...

The controversial ground state and conformation of the tetramethyleneethane diradical (TME) are discussed from ab initio calculations including electronic correlation. results for singlet−triplet energy gap different conformations TME calculated with difference dedicated configuration interaction method (DDCI) presented. They support most reliable experimental hypothesis concerning structures energetics. equilibrium geometries both species have been found to be quite different, D2d symmetry...

A detailed experimental and computational study of the absorption fluorescence spectra 5-aminouracil (5 AU) 6-aminouracil (6 in aqueous solution is reported. The lowest energy band steady-state 5 AU considerably red-shifted, noticeably less intense, broader than its counterpart uracil (U). On contrary, 6 peak close to that U, but it much narrower transition more intense. emission properties AU, U are also very different. Both amino-substituted compounds exhibit indeed a larger Stokes shift...

Phenalenone (PN) is a very efficient singlet oxygen sensitiser in wide range of solvents. This work uses ab initio quantum chemical calculations (CASSCF/CASPT2 protocol) to study the mechanism for populating triplet state PN responsible this reaction, 3(π–π*) state. To describe detail reaction path, and low-lying excited states have been studied, critical points potential energy surfaces corresponding these located vertical adiabatic energies calculated. Our results show that, after initial...

The spirooxazine/merocyanine couple constitutes a photochromic system that can change from the colorless spirooxazine to intensely colored merocyanine by thermal or photochemical activation reaction opens spiro ring of oxazine. mechanisms ring-opening/closure reactions interconnect these two isomers have been elucidated means computational study. First, we used CASSCF/CASPT2 method determine in detail gas phase for small model contains photoactive part whole system. We found state excited...