The effects of ethynyl substitution on the electronic structure of cyclobutadiene are investigated in this work. Ethynyl substituted cyclobutadienes may be involved in Bergman cyclization reactions and are possible intermediates in the formation of fullerenes and graphitic sheets. Prediction of the electronic structure of cyclobutadiene is challenging for single-reference ab initio methods beca...

Computations at the CASPT2, CBS-QB3, and B3LYP levels of theory demonstrate that -substitution of vinyl cations with π-donors switches the ground state of these ions from the familiar closedshell singlet state to a carbene-like triplet state similar to the electronic state of triplet phenyl cations. Although the parent vinyl cation is a ground-state singlet species with a very large energy gap ...

Computations at the CASPT2, CBS-QB3, and B3LYP levels of theory demonstrate that beta-substitution of vinyl cations with pi-donors switches the ground state of these ions from the familiar closed-shell singlet state to a carbene-like triplet state similar to the electronic state of triplet phenyl cations. Although the parent vinyl cation is a ground-state singlet species with a very large energ...

We present high-field (,50 T) photoluminescence measurements of the binding energy of the singlet and triplet states of the negatively charged exciton in a 200-Å quantum well. Comparing our data with those of other groups and with theoretical predictions we clearly show how the singlet, ‘‘bright’’ and ‘‘dark’’ triplet states may be identified according to the high-field dependence of their bind...

The synthesis and photophysical characterization of a palladium(II) porphyrin - anthracene dyad bridged via short and conformationally rigid bicyclo[2.2.2]octadiene spacer were achieved. A spectroscopic investigation of the prepared molecule in solution has been undertaken to study electronic energy transfer in excited singlet and triplet states between the anthracene and porphyrin units. By us...

By using density functional theory (DFT) in B3LYP/6-311++G(d, p) level of theory and conductor-like polarizable continuum modem (CPCM) we examined solvent effects on energy levels in C 5 H 4 for both singlet and triplet states. For this purpose, different solvents, such as gaseous and aqueous solvents, Diethyl ether, Nitro methane, DMSO, Acetonitrile, Methanol, Ethanol, Acetone, Dichloroethane,...

Donor-bridge-acceptor triads consisting of the Alq3 complex, oligofluorene bridge, and PtII tetraphenylporphyrin (PtTPP) were synthesized. The triads were designed to study the energy level/distance-dependence in energy transfer both in a solution and in solid state. The materials show effective singlet transfer from the Alq3-fluorene fluorophore to the porphyrin, while the triplet energy trans...

The population of the lowest triplet state of thymine after near-UV irradiation has been established, on the basis of CASPT2//CASSCF quantum chemical calculations, to take place via three distinct intersystem crossing mechanisms from the initially populated singlet bright 1pipi* state. Two singlet-triplet crossings have been found along the minimum-energy path for ultrafast decay of the singlet...

The molecular mechanism of the thermal rearrangement of singlet 1H-bicyclo[3.1.0]hexa-3,5-dien-2-one to give triplet 4-oxocyclohexa-2,5-dienylidene has been investigated using density functional theory (B3LYP and M05-2X functionals) as well as ab initio CASSCF and CASPT2 multiconfigurational methods. The reactant has a singlet ground state while the product can be found in three low lying elect...

Carotenoid spheroidene (SPO) functions for photoprotection in the photosynthetic reaction centers (RCs) and effectively dissipates its triplet excitation energy. Sensitized cis-to-trans isomerization was proposed as a possible mechanism for a singlet-triplet energy crossing for the 15,15'-cis-SPO; however, it has been questioned recently. To understand the dissipative photoprotective mechanism ...