A laser flash photolysis and time-resolved resonance Raman study of 1-nitronaphthalene (1NN) in sodium nitrite and trans-stilbene (tS) solution, in both polar and nonpolar solvents, is reported. The ...transient absorption data suggest that 1NN acts as an electron acceptor with nitrite ions and tS in polar solvents but undergoes energy transfer to tS in nonpolar solutions. At high concentrations of tS the electron-transfer reaction leads ultimately to the formation of a dimer radical cation (tS2)•+. We report here the Raman spectrum of the radical anion of 1-nitronaphthalene and the differences in the Raman spectra of the monomeric and dimeric radical cation of trans-stilbene in the 1500−1650 cm-1 region. The switch from energy to electron transfer when going from nonpolar to polar solutions is discussed in terms of the electronic and nuclear factors that govern these reactions.
The hierarchical equations of motion (HEOM) theory is one of the standard methods to rigorously describe open quantum dynamics coupled to harmonic environments. Such a model is used to capture ...non-Markovian and non-perturbative effects of environments appearing in ultra-fast phenomena. In the regular framework of the HEOM theory, the environment correlation functions are restricted into linear combinations of exponential functions. In this article, we present a new formulation of the HEOM theory including treatments of non-exponential correlation functions, which enables us to describe general environmental effects more efficiently and stably than the original theory and other generalizations. The library and its Python binding we developed to perform simulations based on our approach, named LibHEOM and PyHEOM respectively, are provided as supplementary material.
Amorphous nanoparticles of the singlet fission chromophore 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pn) are fully crystallized through co-precipitation with a chemical additive. ...Time-resolved measurements indicate that singlet fission in the crystalline nanoparticles is quantitative, or lossless, whereas losses are evident in the amorphous nanoparticles as a result of frustrated triplet pair separation. Because triplet pairs form rapidly and separate slowly in amorphous material, mixed-phase samples are unable to compensate for these losses.
Solution-processable, crystalline material is found to be a promising target for quantitative, or lossless, singlet fission.
Singlet state (S1) radiative and non-radiative decay rates and S1 polarisabilities have been determined for naphthalene dimers where the chromophores are separated by a rigid polynorbornane bridge of ...varying length corresponding to 2, 4 and 6 σ-bonds. The dramatic increase in S1 radiative rates and polarisabilities as interchromophore separation is reduced is attributed to the contribution of a `through-configuration' interaction (involving interchromophore charge-transfer states) to the electronic coupling.
Integrated three-pulse stimulated echo peak shift data are compared for N,N-bis-dimethylphenyl-2,4,6,8-perylenetetracarbonyl diamide and poly2-(2{sup '}-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene ...(MEH-PPV) in toluene solvent. These two molecules represent a model probe of solvation dynamics and a prototypical soluble, electroluminescent conjugated polymer, respectively. The results indicate that it is inappropriate to describe the linear absorption spectrum of MEH-PPV as being primarily inhomogeneously broadened. Conformational disorder along the polymer backbone gives rise to an ensemble of polyene electronic oscillators that are strongly coupled to each other. As a consequence, fluctuations in the electronic energy gap on a time-scale of 50-fs derive primarily from bath-mediated exciton scattering. The data reported here provide an explanation for the broad, structureless electronic absorption of MEH-PPV. This interpretation provides a valuable insight into the nature of the initial photoexcited state, and the efficient population of the emissive state. (c) 2000 The American Physical Society.
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