Charge separation in photoinitiated electron-transfer systems with polyviologen polyelectrolytes as quenchers

Abstract

1937rings, respectively. This suggestion is consistent with the observed Si/Al ratio for ferrierite. The present calculations further indicate that diagonal pairing is favored relative to the meta or ortho pairings in accordance with electrostatic principles and the aluminum avoidance rule.2. As observed in our previous work on mordenite and ZSM-5, the analysis of the formal atomic charges distributions in the clusters indicates the highly covalent nature of aluminosilicate frameworks. The spreading of the negative charge; associated with the presence of Al, indicates that the anionic framework behaves as weak but a soft base.The results presented in this paper complement our earlier findings16J7 and confirm the general principles which have been delineated to describe the behavior and understand the chemistry of zeolite structures. Acknowledgment.Various polyviologen polyelectrolytes which may participate in photoinitiated electron-transfer reactions have been investigated as quenchers. A spectral study was made of the reduced polyviologen radicals on reducing the polyviologen species using the 2-propanol radical. Some of the mono radicals produced, possessing absorption spectra similar to that of the methylviologen radical cation, are found to produce multiradical species in the time scale of seconds and minutes. The nature of the final reduced products and the types of reactions generating them are discussed. The abilities of the polyviologens to quench the emission of the lowest excited states of the two photosensitizers, R~(bpy),(cN)~ and Ru(bpy)?+, were investigated together with the quantum yields of electron transfer and the rates of their back-reactions by using the laser flash photolysis technique. The highest yield of electron transfer was found for the Ru(bpy),2+-poly(o-xylylviologen) system where the quantum yield of photoinitiated electron transfer was determined to be 0.57. The results were compared to those obtained previously with methylviologen and other polymeric viologen systems. The higher than expected rates of quenching and back-reactions were attributed to hydrophobic interactions between the bipyridine groupings of the photosensitizer and quencher which may overcome the repulsive Coulombic forces between them.

Influence of polystyrenesulfonate on electron transfer quenching of ruthenium trisbipyridine luminescence by viologens: non-covalent assembly and covalent tethering of the ruthenium complex

“…Shielding [Ru(bpy) 3 ] 2+ from water enhances the luminescence quantum yield, 42 since the presence of water increases non-radiative decay. 43 Therefore, localization of the complex in a hydrophobic, water-excluding PSS environment is consistent with the observed increase in emission intensity and lifetime, as well as with the red-shifts of both MLCT absorption and emission maxima. In parallel studies, we have observed that [Ru(phen) 2 dppz] 2+ emission is ''turned on'' when bound to PSS, to almost the same extent as when bound to singlestranded polynucleotide [poly(dA)] at low ionic strength (ESI, Fig.…”

Saccharide-induced modulation of photoluminescence lifetime in microgels

“…Firstly, the gel environment strongly contributes to the decrease of the mobility of [Ru(bpy) 3 ] 2+ . 58 Shielding [Ru(bpy) 3 ] 2+ from water should therefore also promote lifetime enhancement. 57 They established a correlation between the lifetime and fluorescence anisotropy, and showed that the cross-linked environment restricted the probe mobility.…”

Polyviologen as Electron Transport Material in Photosystem I-Based Biophotovoltaic Cells

“…Polyviologens first attracted attention when Sassoon et al reported the participation of various polyviologen derivatives in photoinitiated electron-transfer reactions through quenching photoluminescent ruthenium complexes. 17 The quenching behavior confirms that polyviologens rapidly accept excitedstate electrons. This was further evidenced by the later observation that photoexcited CdSe quantum dots transfer electrons to poly(p-xylylviologen) when two materials are prepared into composite solid-state films.…”

“…Polyviologens, first reported in 1971, are a unique class of organic polycationic polymers, with alternating copolymer structure featuring a viologen ( N , N -disubstituted-4,4-bipyridinium dication) and a variable linker group connecting the viologen groups . Aliphatic and unsaturated hydrocarbons of various carbon chain length (e.g., 3–11), as well as aromatic linker groups, have been synthesized and characterized previously. − A generalized polyviologen structure is presented in Figure , along with the structure of a commonly cited polyviologen derivative, poly­( p -xylylviologen). Although most commonly reported redox polymers involve multistep synthetic routes, polyviologens can be easily synthesized from low-cost precursors in a single step.…”