The real-time intramolecular electronic excitation transfer dynamics of 9′,9-bifluorene and 2′,2-binaphthyl in solution

Abstract

The dynamical behavior of intramolecular electronic excitation transfer in 9,9′-bifluorene and 2,2′-binaphthyl has been investigated in various solvents using a heterodyned and background-subtracted femtosecond polarization technique. It has been found that the excitation transfer between fluorenyl moieties occurs on a time scale of around 300 fs in hexane, but evidently slows down to around 970 fs in CCl4, and there appears little observable variation in transfer dynamics when the solvent is changed through the hexane–decane–hexadecane series. It has also been found that excitation transfer between naphthyl moieties in CCl4 undergoes damped oscillations which have an apparent period of 1.2±0.1 ps and a damping time constant of 180±20 fs. While there is no clear sign of any oscillation in hexane, the transfer dynamics decays only slightly faster. All the phenomena observed can be neatly categorized, within the simple phenomenological Bloch theory, as either over- or underdamped motion relevant to the ratio of the exciton splitting to the pure dephasing rate. However, it is the thorough analysis of all the secular elements of the Redfield relaxation matrix that pinpoints the role of correlated fluctuations in the excitation transfer, and provides a quantitative relation of the pure dephasing between the excited local states to that between the excited and ground states. The equivalency of the pure dephasing rate between the two local states to the population transfer rate between the two delocalized states also prompts us to propose that a local libration of solvent CCl4 could play a key role in underdamping the excitation transfer coherence.

A method for the direct measurement of electronic site populations in a molecular aggregate using two-dimensional electronic-vibrational spectroscopy

“…It represents, to our knowledge, the first experimental technique that directly links the energetic dynamics of electronic excitations with spatial information describing where in the complex the excitation is located, on the scale of individual pigments. Other experiments, such as time resolved fluorescence or transient absorption anisotropy, [66][67][68] 2DES with polarization control, 19,20 and coherent nonlinear frequency generation, 69 can provide indirect information which, when assisted by a model, can inform our understanding of the link between the excitonic and spatial structures, but they will always be strongly dependent on the details and quality of the model. 2DEV is capable of providing a direct experimental link between these representations and shows promise in aiding the development of a more complete picture of excitonic dynamics in molecular aggregates.…”

Theoretical Study on Exciton Dynamics in Dendritic Systems: Exciton Recurrence and Migration

“…On the other hand, the coherent dynamics of exciton or electron in super- and supra-molecules have been intensively investigated toward a fundamental understanding of dynamics of excited states and a new development of molecular-based nano-scale devices [ 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 ]. The coherent excitation by irradiation of laser fields creates superposition states composed of plural excited states, which cause the spatial oscillation of excitation, i.e., exciton recurrence motion.…”

Chemical reaction dynamics of some simple molecules in solution

“…In addition, the anisotropy can help unravel the complex kinetic behaviour that can arise from overlapping signals of different species that are involved in a reaction (Cross et al 1983;Sension et al 1993). In the solution phase, anisotropy measurements have enabled the study of excited state energy transfer between identical chromophores (Kim et al 1989;Zhu et al 1993), the dynamics and energy transfer within proteins (Haran et al 1996), the alignment of reactant and product states (Sension et al 1993), and the angular effects of the coupling of internal and overall motions of molecules (Raftery et al 1993;Sension et al 1993). In the present work anisotropy measurements are applied to the impulsive photochemical dissociation fo HgI 2 which generates iodine atoms and HgI molecules.…”