DOI: 10.1002/cphc.201100802 Spontaneous Ionization of N-Alkylphenothiazine Molecules Adsorbed in Channel-Type Zeolites: Effects of Alkyl Chain Length and Confinement on Electron Transfer Sonia CarrØ, [a] Florence Luchez, [a] Alain Moissette,* [a] Olivier Poizat, [a] and Isabelle Batonneau-Gener [b] 1. Introduction The study of molecular systems made up of electron donors in close proximity to electron acceptors has been the subject of numerous works. The key goal shared by all these studies is the understanding of the electron-transfer mechanisms. Indeed, a real control of the electronic and spatial properties of such systems is indispensable to be able to predict and ori- entate the reaction pathway and consequently to optimize the systems in view of applications. Therefore, the development of efficient molecular electronic devices or the mimicry of photo- synthetic centers closely depends on such data, and thus it is of primary importance to characterize the intermediates of the reactions to reveal the electron-generation and subsequent electron-transfer processes. However, the main problem en- countered in these systems is the existence of rapid back elec- tron transfer, which shortens dramatically the lifetime of the charge-separated state. Various new donor–acceptor hybrid systems based on entities such as fullerenes, [1, 2] dyads, [3, 4] and microporous and mesoporous molecular sieves [5–13] were pro- posed to improve the stability of charge-separated states. Among these systems, zeolites are particularly interesting be- cause of their shape- and size-selective internal void space and the high reactivity of the internal surface accessible to the guest molecules. [7, 14] In particular, the remarkable properties of the micropore volume can lead to spontaneous ionization of an electron-donor molecule incorporated in the zeolite and to stabilization of charge-separated states for very long times. [15–17] The mechanism of spontaneous charge separation has been well characterized and reported even in the case of polyaromatic molecules with relatively low ionization potential occluded in channel-type zeolites. Numerous works have already been carried out to under- stand and characterize the host–guest interactions. [18–20] Never- theless, some of the parameters that control the reaction and the subsequent electron transfer remain unclear and require complementary investigations. Previous experiments showed that the spontaneous ionization of low-ionization-potential molecules could occur only within a highly polarizing internal space. The ionization yield and rate depend on the Si/Al ratio of the zeolite lattice and on the nature of the charge-balancing cation because it can induce a strong intrazeolite electrostatic field. [21] Note that the highly polarizing small H + or Li + cations induce long-lived charge-separated states. [22, 23] The effect of the confinement was also shown to be of high importance for electron transfer. [24, 25] N-Methylphenothiazine (m-PTZ) and The mere mixing of N-alkylphenothiazines with three channel- type acid zeolites with various structures (ferrierite, H-MFI, and mordenite) induces the spontaneous ionization of the hetero- cyclic molecule in high yield upon adsorption. The diffuse re- flectance UV–visible absorption and Raman scattering spectra show that the accessibility of the highly polarizing acid sites is not indispensable to induce the spontaneous ionization pro- cess. Due to their particularly low ionization potential values (6.7 eV), the adsorption of the molecules on the external sur- face or in the inner volume is the key parameter to generate the radical cation. However, the ionization yield and charge stabilization are intimately correlated to the possibility of the zeolites accommodating molecules inside their channels. More- over, the higher electrostatic field gradient induced by high confinement is required to favor the second ionization and di- cation formation. The alkyl chain length plays a decisive role by either slowing down the diffusion process or blocking the molecule at the pore entry. Therefore, the efficiency of the ion- ization process that depends on the number of adsorbed mol- ecules decreases significantly from phenothiazine to the N-al- kylphenothiazines. The spectral data demonstrate that defor- mation of the alkyl group is necessary to allow the diffusion of the molecules into the channels. [a] Dr. S. CarrØ, Dr. F. Luchez, Prof. A. Moissette, Dr. O. Poizat Laboratoire de Spectrochimie Infrarouge et Raman UMR-CNRS 8516 Bât. C5 UniversitØ de Lille 1 59655 Villeneuve d’Ascq cedex (France) E-mail : alain.moissette@univ-lille1.fr [b] Dr. I. Batonneau-Gener Laboratoire de Catalyse en Chimie Organique UMR-CNRS 6503 UniversitØ de Poitiers 40 Avenue du Recteur Pineau 80022 Poitiers (France) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cphc.201100802. 504  2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemPhysChem 2012, 13, 504 – 513