Excited-state photophysics

Khopde, S.M. et ah. Effect of solveut ou the excited-state photophysical properties of curcumin, Photochem. Photobiol., 72, 625, 2000. 

Figure 3.2 Jablonski diagram for an organic molecule, illustrating excited-state photophysical processes...

As we have discussed in depth elsewhere, despite the similarities in the structures of hypericin and hypocrellin, which are centered about the perylene quinone nucleus, their excited-state photophysics exhibit rich and varied behavior. The H-atom transfer is characterized by a wide range of time constants, which in certain cases exhibit deuterium isotope effects and solvent dependence. Of particular interest is that the shortest time constant we have observed for the H-atom transfer is 10 ps. This is exceptionally long for such a process, 100 fs being expected when the solute H atom does not hydrogen bond to the solvent [62]. That the transfer time is so long in the perylene quinones has been attributed to the identification of the reaction coordinate with skeletal motions of the molecule [48, 50]. 

To review all of the previously reported upper excited state photophysics and photochemistry as well as processes reported for excited reaction intermediates would require substantially more than a single chapter in this volume. For this reason, I have limited the scope of the chapter to include only the chemistry and photophysics of upper excited states and the chemistry and photophysics of excited radicals of organic systems. 

In order to study solvent effects on the excited state photophysical properties and nonradiative decay of uracil, additional na-AIMD simulations of uracil in liquid water have been carried out [64], Figure 10-7 shows the periodic simulation cell containing uracil and 39 water molecules. We have verified that at any time in... 

Kincaid and co-workers have exploited the steric effect in altering the excited-state photophysical properties of [Ru(bpy)2(daf)] +, where daf = 4,5 diazafluorene [32]. Aqueous solutions of this complex exhibit very weak luminescence, with lifetimes shorter than 10 ns at room temperature. Upon encapsulating this molecule into zeolite Y supercages, the fluorescence intensity increases by a factor of 100 and the excited-state lifetime is increased to 302 ns. 

Many fine books on organic excited states, photophysics, and photochemistry are already available. Ours attempts to offer a different perspective by placing primary emphasis on qualitative theoretical concepts in a way that we hope will be useful to students of physical organic chemistry. 

Abstract This chapter examines the structural characterisation of isolated neutral amino-acids and peptides. After a presentation of the experimental and theoretical state-of-the-art in the field, a review of the major structures and shaping interactions is presented. Special focus is made on conformationally-resolved studies which enable one to go beyond simple structural characterisation probing flexibility and excited-state photophysics are given as examples of promising future directions. 

Chiral recognition, enantioselectivity, and influence of room temperature CILs (RTIL) synthesized from 1-methyl imidazole and chloromethyl menthyl ether on excited-state photophysics of (5)-Ai-methyl-2-pyrrolidinemethyl 2(5)-(6-methoxy-2-naphthyl)propionate [(5,5)-NPX-PYR] was recently investigated using a fluorescence lifetime [114]. The chemical structures of the CILs and chiral analytes used for the lifetime study are shown in Fig. 21, left. The lifetime fluorescence decay of [(5,5)-NPX-PYR] in RTIL chiral environment is shown in Fig. 21, right. 

The effect of thione structure and rigidity on the excited state photophysical and photochemical decay constants [60,64,67,73]... 

Pillsbury, N., and T.S. Zwier. 2009. Conformation-specific spectroscopy and excited state photophysics of 5-phenyl-l-pentene. 7. Phys. Chem. 113A 118-125. 

---