Photochemistry of Azobenzene in Microporous Aluminophosphate AlPO₄-5

Abstract

Photochemical studies of molecules in the organized voids of microporous frameworks is an area of considerable research interest. In this study, we have examined the spectroscopy and photochemistry of trans-azobenzene introduced into the 8 Å channels of an aluminophosphate framework, AlPO4-5. The acidity of aluminophosphates is considered to be very weak, based on their poor catalytic performance in transformations of organic compounds. However, we report that the Brönsted acidity of the AlPO4-5 is enough to protonate the azo groups in azobenzene. This leads to appearance of a band at 418 nm. Also, room temperature emission observed at 518 nm, an unusual spectroscopic feature for azobenzene, is due to the protonated form. Photolysis of the azobenzene/AlPO4-5 sample leads to the formation of benzo[c]cinnoline and benzidine. The Lewis acid sites of AlPO4-5 are proposed to play an important role in the photocyclization chemistry. Because the number of such acid sites in AlPO4-5 is limited, only a fraction of the azobenzene molecules undergo photocyclization. The rest exhibit reversible cis−trans photoisomerization in the presence of visible and ultraviolet irradiation.

Mesostructured Silica Supports for Functional Materials and Molecular Machines

“…Backfilling from either the solution or gas phase is a common method for loading active guests into zeolitic materials. [32,54,55] Using a combination of backfilling and photoexcitation, the ability of zeolites to selectively incorporate molecules of a certain size but exclude those larger has been used to isolate pure samples of molecules that otherwise exist in a cis/trans equilibrium. [56] In mesoporous silicate materials, there are cases in which non-covalent modification is desirable.…”

Photochemistry of azobenzene in sol–gel systems

“…5a shows the absorption spectrum of AB in the xerogel prepared with 200 μL of 1 M HCl. It should be noted here that the absorbance around 320 nm relatively decreases in comparison with that around 420 nm, indicating an increase in a fraction of the protonated trans-AB for the xerogel with ten times concentrated HCl [7,27]. A band of 250 nm appears with a doubled intensity of the 322 nm band after UV irradiation for 1 h (Fig.…”

“…The photochemical studies of AB and its derivatives have been done in various environments such as Nafion membranes, cyclodextrins, zeolites, aluminophosphate, sol-gel glasses, lysozyme, and so on [4][5][6][7][8][9][10][11][12][13][14][15]. The inversion mechanism is considered to be operative in these environments, because the rotation channel is obstructed in such a restricted space.…”

“…Corma et al reported that photolysis of AB in the presence of a series of acidic zeolites gives rise to BC and BZ [6]. Lei et al also reported that photolysis of AB in aluminophosphate leads to the formation of BC and BZ and the Lewis acid sites of aluminophosphate are considered to play an important role in the photocyclization chemistry [7].…”

Microscopy and optical manipulation of dendrimer-built vesicles

“…azobenzene in restricted environments with a maximum near that reported by Rau at low pH [14,15]. A different type of emission with a λ max = 600 nm was observed for aggregated azobenzene chromophores in bilayers by Shimomura and Kunitake [16].…”