The elementary steps of the photodissociation and recombination reactions of iodine molecules enclosed in cages and channels of zeolite crystals: A femtosecond time-resolved study of the geometry effect

Abstract

We present femtosecond time-resolved pump-probe experiments on iodine molecules enclosed into well-defined cages and channels of different crystalline SiO2 modifications of zeolites. The new experimental results obtained from iodine in TON (Silica-ZSM-22), FER (Silica-Ferrierit), and MFI (Silicalit-1) porosils are compared with data published earlier on the iodine/DDR (Decadodecasil 3R) porosil system [Flachenecker et al., Phys. Chem. Chem. Phys. 5, 865 (2003)]. A summary of all findings is given. The processes analyzed by means of the ultrafast spectroscopy are the vibrational relaxation as well as the dissociation and recombination reactions, which are caused by the interaction of the photo-excited iodine molecules with the cavity walls of the porosils. A clear dependence of the observed dynamics on the geometry of the surrounding lattice structure can be seen. These measurements are supported by temperature-dependent experiments. Making use of a theoretical model which is based on the classical Langevin equation, an analysis of the geometry-reaction relation is performed. The Brownian dynamics simulations show that in contrast to the vibrational relaxation the predissociation dynamics are independent of the frequency of collisions with the surroundings. From the results obtained in the different surroundings, we conclude that mainly local fields are responsible for the crossing from the bound B state to the repulsive a/a' states of the iodine molecules.

Femtochemistry of orange II in solution and in chemical and biological nanocavities

“…The increase in emission intensity in the presence of CDs is explained in terms of increase of trans-AZO population upon encapsulation and restriction in motion of caged and photoproduced HYZ structure. However, 13 C-T 1 measurements have shown that for some populations of OII:␤-CD complexes, the guest molecule still can move within the cavity (26,27).…”

“…The inclusion complexes of OII and CDs have been studied by several groups showing the formation of a 1:1 entity (24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35). So far, the CD inclusion complex studies have considered that OII in water solutions exists under AZO tautomer, contrary to many studies in solutions where OII coexists under AZO and HYZ forms (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). Recently, ultrafast transient lens technique with a response function of Ϸ300 fs has been used to study the dynamics of OII in CD (36).…”

“…Therefore, simple and complex (in concept) molecular systems have been studied using cyclodextrins (CDs), proteins, micelles, pores, and zeolites as nanohosts, demonstrating the confinement effect of the hydrophobic nanocavities on the spectroscopy and dynamics of the guests (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13). Relevant information on the ultrafast dynamics of caged wavepackets involving breaking͞making chemical bonds, and solvation has been acquired.…”

Supramolecular Organization in Confined Nanospaces

“…The environmental relevance of toxic gas capture and the electric conductivity enhancement caused by iodine uptake, have raised great interest on the incorporation of dihalogen molecules in diverse hosts like clathrasils,, zeosils,, and ALPOs, but also organic salts, organic zeolites, Hofmann clathrates,, and other MOFs …”

Electrical and Optical Properties of Nanocomposites Fabricated by the Introduction of Iodine in Porous Dielectric Matrices

“…In this study, a hole-type conducting semiconductor iodine was used as the guest substance. It is often considered as the model object when creating and studying various nanostructures in solid-state physics [5][6][7][8][9][10][11][12][13][14][15] and has prospects for practical application in electronics [16], photonics [17], and medicine [18] (where zeolite matrices can be used for targeted drug delivery [19]).…”