Ultrafast nonradiative dynamics

In this article we mainly focus on the central issue of vibronic coupling in the benzenoid systems viz., the phenyl radical (Ph ) and phenylacetyleneradical cation (PA +) and the lowest members of the family of the PAH radical cations viz., naphthalene (N +) and anthracene (AN +) radical cations. Consequences of this coupling for the nuclear dynamics of these systems are studied at length. The difficulties faced in the quantum mechanical treatments of these large systems are also discussed. Dynamical observables like the rich vibronic spectrum are calculated and assigned. The ultrafast nonradiative dynamics of the excited states is also studied. These observables are compared with the available experimental data to validate the established theoretical model [19-22]. 

Studzinski, H., Zhang, S., Wang, Y, Temps, F. (2008) Ultrafast Nonradiative Dynamics in Electronically Excited Hexafluorobenzene by Femtosecond Time-resolved Mass Spectrometry. J. Chem. Phys. 128 164314. 

Among the best well-known examples of photostability after UV radiation, the ultrafast nonradiative decay observed in DNA/RNA nucleobases, has attracted most of the attention both from experimental and theoretical viewpoints [30], Since the quenched DNA fluorescence in nucleobase monomers at the room temperature was first reported [31] new advances have improved our knowledge on the dynamics of photoexcited DNA. Femtosecond pump-probe experiments in molecular beams have detected multi-exponential decay channels in the femtosecond (fs) and picosecond (ps) timescales for the isolated nucleobases [30, 32-34], The lack of strong solvent effects and similar ultrafast decays obtained for nucleosides and nucleotides suggest that ultrashort lifetimes of nucleobases are intrinsic molecular properties, intimately... 

Abstract The study of the fate of electronically excited radical and radical cation of aromatic hydrocarbons is an emerging topic in modern chemical dynamics. Observations like low quantum yield of fluorescence and photostability are of immediate concern to unravel the mechanism of ultrafast nonradiative internal conversion dynamics in such systems. The radical cations of polycyclic aromatic hydrocarbons (PAHs) have received considerable attention in this context and invited critical measurements of their optical spectroscopy in a laboratory, in striving to understand the enigmatic diffuse interstellar bands (DIBs). 

To conclude, we have established the role of intricate nonadiabatic coupling in the dynamics of electronically excited radical cations of PAH. The theoretical results presented above support the experimental data on ultrafast nonradiative decay and... 

Nieber, H., 8c Doltsinis, N. L. (2008). Elucidating ultrafast nonradiative decay of photoexcited uracil in aqueous solution byab initio molecular dynamics. Chemical Physics, 347(1-3), 405-412. doi 10.1016/j.chemphys.2007.09.056. 

Cohen B, Hare P, Kohler B (2003) Ultrafast excited-state dynamics of adenine and monomethy-lated adenines in solution implications for the nonradiative decay mechanism. J Am Chem Soc 125 13594... 

The vibronic spectra of Do — Di — D2 electronic states recoded by da Silva Filho et al. [45] revealed resolved vibrational structures of the Do and D2 electronic states and a broad and structureless band for the Di state. A slow ( 3-20 ps) and fast k, 200 fs) relaxation components are estimated for the Dq D2 transition in a (femto)picosecond transient grating spectroscopy measurements [16]. The fast component is attributed to the Do D2 transition and a nonradiative relaxation time of 212 fs is also estimated from the cavity ringdown (CRD) spectroscopy data [42]. Electronic structure results of Hall et al. [107] suggest that the nonradiative Do D2 relaxation occurs via two consecutive sloped type CIs [66,108]. We developed a global model PESs for the Do — Di— D2 electronic states and devised a vibronic coupling model to study the nuclear dynamics underlying the complex vibronic spectrum and ultrafast excited state decay of N +[20]. 

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