Fluorescence Spectra of Pyrene and Humidity Effects on Them during the Sol-to-Gel-to-Xerogel Transitions of Mixed Silicon–Aluminum Alkoxide Systems

Abstract

The fluorescence spectra of pyrene of four sol systems comprising silicon and aluminum alkoxides (Si : Al = 99.4 : 0.6 ; 93.6 : 6.4; 85.9 : 14.1; and 50 : 50) have been observed during sol-to-gel-to-xerogel transitions under at relatively low concentration, on the order of 10−4 mol dm−3, uncatalyzed, and constant temperature (300 K) conditions. The influence of relative humidity on the relative intensities of pyrene monomer and excimer-like fluorescence in the four xerogel states has also been observed. In three of the four systems studied (all but Si : Al = 99.4 : 0.6), fluorescence spectra revealed that excimer concentration increased with time and reached a maximum near 55 days after which it decreased. From our data, it is apparent that the ratio of the intensity of the excimer-like fluorescence to that of the monomer fluorescence increases with relative humidity.

Fluorescence Properties of 2,5-Bis(4-(diethylamino)phenyl)-1,3,4-oxadiazole Molecules Encapsulated in SiO2 and Si−Ti Binary Oxide Matrixes by the Sol−Gel Method

“…During the gelation, the formation of the O−Si−O−Ti−O networks is completed for the systems to form many various micropores. As shown in Figure , it is clear that, in the Ti/Si binary oxides having lower Ti content such as Ti(1), highly dispersed 4-fold coordinated Ti oxide species are formed in the oxides and play the role of effective adsorption sites. , Therefore, when more than two BDD molecules are in the same pore, such Ti oxide species promote formation of “bimolecular ground-state associations” (BGSA's) or configurations of BDD molecules. , In the initial stage of the gelation, BDD molecules are trapped in the pore together with H 2 O, ethanol, and/or isobutanol. However, with the gelation, these solvent molecules evaporated, leading to condensation of BDD molecules, which results in an increase of the excimer fluorescence.…”

Growth and characterization of pyrene crystals on carbon nanofibers

“…The fluorescence spectrum of Supernatant A excited at 335 nm exhibits a dual fluorescence. One is the vibronic bands seen at 372-392 nm and is assigned to the pyrene monomer in water [26,32,33]. The other is the broad band, which has a peak at 460 nm, due to an excimer-like fluorescence, as observed in the spectrum at the 360 nm excitation.…”