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Pentacene is an important model organic semiconductor in both the singlet exciton fission (SF) and organic electronics communities. We have investigated the effect of changing crystal structure on the SF process, generating multiple triplet excitons from an initial singlet exciton, and subsequent triplet recombination. Unlike for similar organic semiconductors that have strong SF sensitive to polymorphism, we find almost no quantitative difference between the kinetics of triplet pair (TT) formation in the two dominant polymorphs of pentacene. Both pairwise dimer coupling and momentum-space crystal models predict much faster TT formation from the bright singlet excited state of the Bulk vs ThinFilm polymorph, contrasting with the experiment. GW and Bethe–Salpeter equation calculations, including exciton–phonon coupling, reveal that ultrafast phonon-driven transitions in the ThinFilm polymorph compensate the intrinsically slower purely Coulomb-mediated TT formation channel, rationalizing the similarity in observed rates. Taking into account the influence of subtle structural distinctions on both the direct and phonon-mediated SF pathways reveals a predictive capability to these methods, expected to be applicable to a wide variety of molecular crystals. [ABSTRACT FROM AUTHOR]

A multivariate statistical analysis is used to extract a single control variable from results of 137 parameter adaptive laser pulse shaping optimization of multiphoton electronic excitation in Rh(II) coordination complex in solution. It is shown that this single variable can be sued to linearly manipulate the observed fitness which is determined by the ratio of molecular emission to second harmonic generation of the laser pulse.

The development of adaptive control algorithm with physiochemical control pathways in arbitrary complex molecular system which could be used to measure second-harmonic spectra of shaped laser fields is reported. The adaptive control experiment can be used to understand spectral control pathways of the molecule in solution.

A generally applicable method is presented for the dimension reduction of adaptive control experiments based on partial least squares regression analysis (PLS) of the normalized covariance matrix of the total data set. Experimental results shows that only seven fundamental dimensions from an original 208-dimension search space are needed to account for approximately 90% of the variance in the observed fitness of 11700 laser-pulse shapes explored during the optimization experiment.

A study of the transition metal complexes has been conducted by means of the femtosecond visible electronic absorption spectroscopy. Results include identification of the optical marker for the thermalized excited state as a unique absorptive feature.

Research has been conducted on the variable-temperature emission data for bipyridyl complexes of Ru (super)III. Results indicate the increase of the spectra through the glass-to-fluid transition.

Proton-transfer reactions involving the silaformyl anion, HSi[O.sup.-], and its conjugate acids, HSiOH and [H.sub.2]SiO, have been investigated with ab initio methods. Calculations through fourth-order perturbation theory suggest possible routes for proton transfer. Accurate estimates for the acidity of [H.sub.2]SiO and HSiOH are presented and discussed in light of earlier experimental estimates.

A series of aryl-substituted 2,2'-bipyridyl complexes of RuII were synthesized and photophysically characterized. The unusually large radiative quantum yield for (Ru(dpb)3)(PF6)2 in CH3CN solution was found to be due to the reduction of geometric distortion along the ring-stretch acceptor mode coordinates. The 3MLCT excited stae of (Ru(dpb)3) was thought to be characterized by a ligand conformation where the 4,4'-phenyl substituents are coplanar with the bipyridyl fragment.

Researchers experimentally and computationally analyzed the gas-phase reactions of trimethylaluminates with several acids. Methyl cleavage is preferred in the reaction of nine aluminates and HCl. Related calculations for ((CH3)3AlX)- (for X = F and OH) with HCl and intrinsic reaction coordinate calculations for ((CH3)3AlF)- + HCl from the transition state to products outline the transition states and forecast the cleavage results for X and methyl cleavage.

The various mechanisms and dynamics involved in the formation, as well as the trapping of the electron-transfer photoproducts as exhibited by different metal complexes are analyzed. New method for the formation and storage of the different charge-separated excited states are also explained.

The synthesis and spectroelectrochemical characterization of two new ruthenium(II) polypyridyl donor-bridge-acceptor (D-B-A) systems with an excited-state conformationally active bridge along with two new donor-bridge (D-B) model complexes without acceptor is described. The extent of electron delocalization that is acceptable following metal-to-ligand charge transfer excitation provides insight into structurally control of the key factors governing photoinduced electron transfer rates such as reorganization energy and electronic coupling.