Spontaneous Charge Separation and Recombination Induced by Tetracene Incorporation in Pores of Acidic HnZSM-5 Zeolites

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• 作者：S&eacute ; verine Marquis ; Alain Moissette ; Matthieu Hureau ; Herv&eacute ; Vezin ; Claude Br&eacute ; mard
• 刊名：Journal of Physical Chemistry C
• 出版年：2007
• 出版时间：November 22, 2007
• 年：2007
• 卷：111
• 期：46
• 页码：17346 - 17356
• 全文大小：302K
• 年卷期：v.111,no.46(November 22, 2007)
• ISSN：1932-7455

文摘

In situ CW-EPR and diffuse reflectance UV-visible spectroscopy were used to monitor the spontaneousincorporation of ACENE-4 or tetracene (C₁₈H₁₂) in the medium-pore M_nZSM-5 zeolites [M_n(AlO₂)_n(SiO₂)_96-n;M=Na⁺, H⁺; n = 3.4, 6.6] by direct exposure under dry and inert atmosphere of solid ACENE-4 to dehydratedporous materials without any solvent. The sorption of the large ACENE-4 molecule with relatively lowionization potential (6.97 eV) occurs in Brnsted acidic H_nZSM-5 zeolites according to a complex and slowreaction sequence including protonation, charge separation, hole transfer, and charge recombination whileACENE-4 is incorporated as an intact molecule in nonacidic Na_nZSM-5. After a long organization period,ACENE-4 lies in the straight channel in front of sodium cation in close proximity of Al framework atom assimulated by Monte Carlo calculations. The multivariate curve resolution (MCR) analysis of the huge DRUVvspectra set recorded during the ACENE-4 sorption course in acidic H_nZSM-5 resolved successfully the specificabsorption spectra and respective concentrations of all species as function of time. HACENE-4⁺@H_n-1ZSM-5^- protonated species and ACENE-4⁺@H_nZSM-5^- radical pair are generated in the first steps of sorptionwhile a long-lived ACENE-4@H_nZSM-5^-+ electron-hole pair is formed through hole transfer and recombinesslowly to ACENE-4@H_nZSM-5 without any protonation. Two-dimensional hyperfine-sublevel correlation(2D-HYSCORE) experiments reveal the structural surroundings of the unpaired electrons through the properassignment of unpaired electron couplings with ¹H, ²⁹Si, and ²⁷Al nuclei. The tight fit between the rod shapeACENE-4 and the pore size of ZSM-5 zeolites combined with the efficient polarizing effect of proton andaluminum electron trapping sites are the most important factors responsible for the stabilization of the electron-hole moiety and hinder the charge recombination efficiently.