Franck-Condon states

Figure 2.30. SFo, Franck-Condon state Sp, fluorescence state. Reproduced with permission from Ref. 65.

In contrast, if the medium is too viscous to allow solvent molecules to reorganize, emission arises from a state close to the Franck-Condon state (FC) (as in the case of a nonpolar medium) and no shift of the fluorescence spectrum will be observed (F in Figure 7.2). 

Slow reorganization dynamics in the adsorbate/adsorbent complex after excitation of the Franck-Condon state. This could explain the spectral redshift of fluorescence with time (Figure 8.8, upper right, and Figure 8.9). In liquid solution, the excited state equilibrates on the picosecond timescale, but is has been shown(23) that this process can slow down on surfaces to 10-50 nsec. 

Time-resolved femtosecond (fs) absorption spectroscopy has been applied to investigate the earliest events of the decay of [Ru(bpy)3] " and provides information relating to the dynamics associated with the evolution of the Franck-Condon state to the lowest-energy excited state of [Ru(bpy)3]. Within 300 fs of the initial excitation, the latter process is effectively complete. The conclusions of this work are of particular importance in terms of updating the views concerning the relaxation of [Ru(bpy)3]. ... 

The most likely electronic transition will occur without changes in the positions of the nuclei (e.g., little change in the distance between atoms) in the molecular entity and its environment. Such a state is known as a Franck-Condon state, and the transition is referred to as a vertical transition. In such transitions, the intensity of the vibronic transition is proportional to the square of the overlap interval between the vibrational wavefunctions of the two states. See Fluorescence Jablonski Diagram Comm, on Photochem. (1988) Pure and Appl. Chem. 60, 1055. 

On the ultrafast conversions from excited FC (Franck-Condon) state to FI (Fluorescence) state of chromophores in PNS of photoactive proteins PYP, Rh and FP... 

One of the most controversial questions encountered in studies of Cr111 photochemistry concerns the identity of the reactive excited state(s).71 As illustrated in Figure 6, uncertainty can arise because the Franck-Condon state initially populated during irradiation in the quartet absorption bands generally undergoes rapid equilibration to the lowest thexi quartet state, Q°u and/or intersystem crossing to the lowest doublet, D°. Reaction from either or both of the latter states must therefore be considered. 

The enrichment of the concentration of the polar solvent component in the cage and, therefore, the relative amount of the red shift of the fluorescence band is a function of viscosity, since the diffusion-controlled reaction time must be smaller than the excited-state lifetime. This lifetime limitation of the red shift is even more severe if the higher value of the excited-state dipole moment is not a property of the initial Franck-Condon state but of the final state of an adiabatic reaction. Nevertheless, the additional red shift has been observed for the fluorescence of TICT biradical excited states due to their nanosecond lifetime together with a quenching effect of the total fluorescence since the A to 50 transition is weak (symmetry forbidden) (Fig. 2.25). 

The above described model sequences have been studied both as oligomers [7,8,11-13,19] and as polymers [9,11,20]. An increase in the size of the helix is known to reinforce its stability, as revealed by their melting curves [18] and attested by X-ray diffraction measurements in solution [21]. Therefore, in this chapter we focus on the polymeric duplexes poly(dGdC).poly(dGdC) [= 1000 base-pairs], poly(dAdT).poly(dAdT) [= 200-400 base-pairs] and poly(dA).poly(dT) [= 2000 base-pairs] studied by us. First we discuss the absorption spectra, which reflect the properties of Franck-Condon states, in connection with theoretical studies. Then we turn to fluorescence properties fluorescence intensity decays (hereafter called simply fluorescence decays ), fluorescence anisotropy decays and time-resolved fluorescence spectra. We... 

For instance Cr(CO)6+ is formed only during LI. The time-dependent behavior of the ion yields of Cr(CO)6+ is presented in Fig. 13. Deconvolution of the time-dependent ion yield with the instrument function derived from the Xe+ signal provides a measure of the time constant (ij) of 12.5 0.05 fs for the LI level (Table 2). This represents the time it takes for the excited Cr(CO)6 to cross to the repulsive surface through the conical intersection close to the Franck-Condon state. At the Franck-Condon point with Oh symmetry, the only coordinates with nonzero slope are the totally symmetric alg M-C stretch or the Jahn-Teller-active vibrations which have eg or t2g symmetry [32], The time taken for a wavepacket to travel from any... 

The CT complexes are characterized by a new absorption band which is usually red-shifted as compared to local excitation bands [47-49], According to the Mulliken formulation the CT-exdtation corresponds to an electronic transition from the HOMO of the donor to the LUMO of the acceptor, i.e. it accomplishes full electron transfer [47], The transition is instantaneous, producing two intermediates (ions) in a direct contact but in a non-equilibrium, Franck-Condon state. The relaxation of the pair competes with BET, diminishing the quantum yield for ion generation [49], This process is believed to take... 

Fig. 10. Excitation of a donor (or acceptor) takes place as a vertical transition generating a Franck-Condon (FC) state with a different electron configuration but same nuclear geometry as the ground state. The Franck-Condon state undergoes equilibration to a thermalized excited state. In PET, the nuclei of the thermalized excited state (in this case, an electron donor), acceptor, and surrounding molecules undergo a reorganization to the geometry of the transition state. Electron transfer takes place rapidly within the transition state without any appreciable nuclear motion, generating a Franck-Condon-like radical ion pair. The excited radical ion pair subsequently undergoes equilibration to a thermalized ion pair...

On the basis of the Franck-Condon principle, photoelectron transfer between a donor and acceptor molecule proceeds as follows (Fig. 10). Initially, the donor and acceptor are dispersed randomly in a solution. On light absorption, the donor (or acceptor) undergoes a rapid transition to form a Franck-Condon state, which rapidly undergoes nuclear relaxation to an equilibrated state. A further nuclear reorganization takes place before electron transfer. After electron transfer, there is nuclear relaxation to the final, equilibrated product state. 

Franck-condon state See Franck-Condon principle. 

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