Communication: Adjusting charge transfer state energies for configuration interaction singles: Without any parameterization and with minimal cost

In a recent article, we showed that configuration interaction singles (CIS) has a systematic bias against charge-transfer (CT) states: CT vertical excitation energies are consistently too high (by 1-2 eV) as compared with non-CT energies [J. E. Subotnik, J. Chem. Phys. 137, 071104 (2011)]. We now show that this CIS error can be corrected approximately by performing a single Newton- Raphson step to reoptimize orbitals, thus establishing a new set of orbitals which better balances ground and excited state energies. The computational cost of this correction is exactly that of one coupled-perturbed Hartree-Fock calculation, which is effectively the cost of the CIS calculation itself. In other words, for twice the computational cost of a standard CIS calculation, or roughly the same cost as a linear-response time-dependent Hartree-Fock calculation, one can achieve a balanced, size-consistent description of CT versus non-CT energies, ideally with the accuracy of a much more expensive doubles CIS(D) calculation

Vibrational Dynamics of a Perylene–Perylenediimide Donor–Acceptor Dyad Probed with Femtosecond Stimulated Raman Spectroscopy

The ultrafast vibrational dynamics of the photoinduced charge-transfer reaction between perylene (Per) and perylene-3,4:9,10-bis­(dicarboximide) (PDI) were investigated using femtosecond stimulated Raman spectroscopy (FSRS). Specifically probing the structural dynamics of PDI following its selective photoexcitation in a covalently linked dyad reveals vibrational modes uniquely characteristic to the PDI lowest excited singlet state and radical anion between 1000 and 1700 cm^–1. A comparison of these vibrations to those of the ground state reveals the appearance of new ^1*PDI and PDI^–• stretching modes in the dyad at 1593 and 1588 cm^–1, respectively. DFT calculations reveal that these vibrations are parallel to the long axis of PDI and thus then may be integral to the charge separation reaction. The ability to differentiate excited state from radical anion vibrational modes allows the evaluation of the influence of specific modes on the charge transfer dynamics in donor–bridge–acceptor systems based on PDI molecular constructs

CuAAC-based assembly and characterization of a ruthenium–copper dyad containing a diimine–dioxime ligand framework

International audienceThe design of molecular dyads combining a light-harvesting unit with an electroactive centre is highly demanded in the field of artificial photosynthesis. The versatile Copper-catalyzed Azide–Alkyne Cycloaddition (CuAAC) procedure was employed to assemble a ruthenium tris-diimine unit to an unprecedented azide-substituted copper diimine–dioxime moiety. The resulting RuIICuII dyad 4 was characterized by electrochemistry, 1H NMR, EPR, UV-visible absorption, steady-state fluorescence and transient absorption spectroscopies. Photoinduced electron transfer from the ruthenium to the copper centre upon light-activation in the presence of a sacrificial electron donor was established thanks to EPR-monitored photolysis experiments, opening interesting perspectives for photocatalytic applications

Singlet Exciton Fission in Polycrystalline Thin Films of a Slip-Stacked Perylenediimide

The crystal structure of <i>N</i>,<i>N</i>-bis­(<i>n</i>-octyl)-2,5,8,11-tetraphenylperylene-3,4:9,10-bis­(dicarboximide), <b>1</b>, obtained by X-ray diffraction reveals that <b>1</b> has a nearly planar perylene core and π–π stacks at a 3.5 Å interplanar distance in well-separated slip-stacked columns. Theory predicts that slip-stacked, π–π-stacked structures should enhance interchromophore electronic coupling and thus favor singlet exciton fission. Photoexcitation of vapor-deposited polycrystalline 188 nm thick films of <b>1</b> results in a 140 ± 20% yield of triplet excitons (^3*<b>1</b>) in τ_SF = 180 ± 10 ps. These results illustrate a design strategy for producing perylenediimide and related rylene derivatives that have the optimized interchromophore electronic interactions which promote high-yield singlet exciton fission for potentially enhancing organic solar cell performance and charge separation in systems for artificial photosynthesis

Singlet Exciton Fission in Polycrystalline Thin Films of a Slip-Stacked Perylenediimide

The crystal structure of <i>N</i>,<i>N</i>-bis­(<i>n</i>-octyl)-2,5,8,11-tetraphenylperylene-3,4:9,10-bis­(dicarboximide), <b>1</b>, obtained by X-ray diffraction reveals that <b>1</b> has a nearly planar perylene core and π–π stacks at a 3.5 Å interplanar distance in well-separated slip-stacked columns. Theory predicts that slip-stacked, π–π-stacked structures should enhance interchromophore electronic coupling and thus favor singlet exciton fission. Photoexcitation of vapor-deposited polycrystalline 188 nm thick films of <b>1</b> results in a 140 ± 20% yield of triplet excitons (^3*<b>1</b>) in τ_SF = 180 ± 10 ps. These results illustrate a design strategy for producing perylenediimide and related rylene derivatives that have the optimized interchromophore electronic interactions which promote high-yield singlet exciton fission for potentially enhancing organic solar cell performance and charge separation in systems for artificial photosynthesis