Photochemistry of Biphenyl Occluded within X Faujasite Type Zeolites

Abstract

The UV laser flash photolysis (248 nm, 10 ns) of biphenyl (BP) occluded in void space of aluminum rich faujasitic X zeolites Na n (AlO 2 ) n (SiO 2 ) 192-n with n ) 85, 96 has been investigated by diffuse reflectance transient UV-visible absorption (DRTUV) and time-resolved resonance Raman (TR 3 ) measurements on the nanoand microsecond time scales. TR 3 measurements were carried out using an 8 ns probe pulse at 370 nm. Delays between pump and probe pulses (50 ns to 100 µs) provide evidence of triplet state BP(T 1 ), radical cation BP •+ , and radical anion BP •with planar quinoidal structures. Self-modeling mixture analysis (SIMPLISMA) of DRTUV data sets resolved pure absorption spectra of BP(T 1 ), BP •+ , BP •-, and trapped electron as Na 4 3+ . Data processing determines also the decays of the corresponding concentrations between 0.5 and 340 µs for loading values corresponding to 1, 2, 4, and 8 BP per unit cell. All the decays of specific concentration were found to fit a model of dispersed heterogeneous kinetics. At lower laser fluence, BP(T 1 ) was found to be the major transient species for all the loading values. Lifetime mean values of BP(T 1 ) were found to be 40 and 110 µs at low and high loading, respectively. Photoionization was found to be dominant at higher pump laser fluence. At low loading, Na 4 3+ cluster and BP •+ are produced in high yield with relatively different lifetimes, 10 µs and ∼500 µs, respectively. The recombination process includes probably supplementary electron transfers with the zeolite framework. At high loading, BP •-(20 µs) concomitantly forms BP •+ (12 µs) as a result of photoejected electron capture by BP(S 0 ). The most important role of porous solids with large pores such as X faujasite with respect to photophysical and photochemical BP behaviors in solution appears to be the efficient trapping of photoejected electron in the solid network.

Kinetics and characterization of photoinduced long-lived electron–hole pair of p-terphenyl occluded in ZSM-5 zeolites. Effects of aluminium content and extraframework cation

“…The corresponding g distribution coefficients (see Experimental section) range between 2 and 3, in reasonable agreement with other heterogeneous photochemical reactions. 64 The corresponding lifetimes are conventionally represented by 1/ k. The values listed in Table 1 indicate that the p-TP + lifetime is always shorter than that of the electron-hole pair and confirm the abstraction of electrons from the zeolite framework by p-TP + to generate long-lived electron-hole pairs before charge recombination. For all irradiated p-TP@M n ZSM-5 samples, the formation of the p-TP + -electron pairs was very fast, according to eqn (6).…”

Kinetics of electron–hole pair trapping via photoionization of biphenyl occluded in aluminium-rich ZSM-5 zeolites. Effects of extra-framework cations

“…[1][2][3][4][5] Many works concerning the photoionization of BP in solution, adsorbed on silica gel, and occluded in faujasitic zeolites or laponite clays were reported previously and pointed out short-lived BP þ and electron trapped as M n (nÀ1)þ cluster of extraframework cation M þ in aluminium-rich faujasitic zeolites. [6][7][8][9][10][11][12] Previously, we have reported preliminary results of the laser photolysis of BP occluded in non-acidic aluminium poor MFI-zeolites using transient diffuse reflectance transient UV-visible absorption (DRTUVv) and time resolved resonance Raman scattering (TR 3 ) investigations on nano-/microsecond time scale. The BP þ lifetime was found to increase dramatically with the aluminium content.…”

Laser flash photolysis study of anthracene/viologen charge transfer complex in non-polar, dealuminated zeolites

“…[13][14][15][16]18 On the other hand, biphenyl, anthracene (AN) and other aromatics adsorbed on faujasites also generate radical cations upon laser excitation. 19,20 Importantly, AN and MV þþ are among the CT complexes whose charge separated state was observed to decay in the ms timescale.…”