Photochemistry of 2,3-diazabicyclo[2.2.2]oct-2-ene

Abstract

The photochemistry of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) has been investigated in the gas phase and in solution and is compared with that of other azoalkanes. The main fates of DBO in the direct photolysis at low pressures are fluorescence from the , * singlet (Si*) and intersystem crossing to the triplet from which decomposition occurs ( , = 0.56 ± 0.10, ^' = 0.50 ± 0.05 at 0.1 Torr). Return of the DBO molecules from the triplet to the ground electronic state (S0) becomes important at higher gas-phase pressures and particularly in solution. In isooctane ^/" is only 0.022 and ^decCí = 0.014. Irradiation of DBO in solution results in the buildup of a diffusion-controlled singlet quencher; this quencher is not formed in the triplet-sensitized photolysis. Oxygen quenching of 'DBO* in solution occurs via the triplet DBO(Si) + 02-> DBO(Ti), the rate constant for this process being 6 X 109 M~l sec-1. From kinetic measurements the triplet energy, ET, of DBO has been found to ¡De 54.5 kcal mol-1 and the lifetimes of the lowest triplet states of DBO and of 2,3-diazabicyclo[2.2.1 ]hept-2-ene (DBH) in solution have been estimated as being <10-9 sec. The interaction rate constants of triplet benzophenone, naphthyl phenyl ketone, benzil, and biacetyl with a variety of substrates have been determined.I n previous papers we have discussed the photochemistry of azoisopropane (AIP) and 2,3-diazabicyclo-[2.2.1]hept-2-ene (DBH).1'2 345In this paper we report on the photochemistry of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO), give further data for DBH, and draw comparisons between the photochemistry of these three compounds. AIP DBH DBO Experimental SectionMaterials. The preparations of DBH, DBO, and AIP have been described previously.3-6 All reagents were the best grade (1) I.

Time-resolved infrared studies of triplet 1,3-cyclopentanediyl

“…(The concentration of oxygen in saturated acetonitrile solutions is 9.1 mM. 20 ) This analysis leads to a lower limit for the oxygen quenching rate constant k O 2 !2 Â 10 9 l mol À1 s À1 , again in good agreement with previous work. 10 …”

Triplet Energy and Lifetime of 2,3-Diazabicyclo[2.2.2]oct-1-ene

“…11 Earlier, the E T of DBO had been estimated as 54.5 kcal/mol using the same technique. 12 Despite the low quantum yield for nitrogen formation, the photochemistry of DBO has been investigated extensively. [12][13][14] In the present work, we report a direct measurement of the triplet lifetime, τ T , and an estimate of E T of DBO by time-resolved photoacoustic calorimetry (PAC).…”

Photochemical decomposition and isomerization of aliphatic azo compounds

“…12). At 5.5°K, DBH gives the cyclopentan-l,3-diyl biradical but DBO produces no species observable by esr (Ref.…”