Deactivation of the fluorescent state of 9-tert-butylanthracene. 9-tert-Butyl-9,10(Dewar anthracene)

Abstract

7 3 + 200 100 0 PPm Figure 4. ,'P NMR spectrum of [Au9(PPh&] [NO,], (CP time 5 ms, pulse interval 5 s, 4710 accumulations, spinning rate 3.5 kHz). ciation reactions.9c The only well-studied compound is [ ( ( M~O ) , P ) , C U ] ' .~~~~~~The Cu atom in (Ph3P)2CuN03 is tetrahedrally coordinated to the two phosphorus atoms and two oxygen atoms of the NO3group.IO The two triphenylphosphine groups are equivalent. The solid-state ''P NMR spectrum of (Ph3P)2CuN03, Figure 2, shows four main peaks at +26.0, +13.1, -7.0, and -31.1 ppm, the outer peaks accompanied by satellite peaks at +28.3 and -33.1 ppm. The 65Cu isotope (abundance 63Cu 69.09%, 30.91%) seems to be responsible for these satellite peaks.Because the crystal structurelo shows that all phosphine groups are equivalent, the splitting of the phosphorus resonance line into four peaks has to be caused by coupling of the phosphorus spin ( I = to the Cu spin ( I = 3/2 for both isotopes). Surprisingly, the splitting between the lines of this quartet increases to higher field. An explanation of this effect may be that due to the presence of a Cu quadrupole interaction not small compared to the Cu Zeeman interaction, the Cu-P dipolar and J tensor interactions are not averaged out by magic angle spinning. Then, in addition to the isotropic J coupling, also the dipolar and J tensor interactions contribute to the splitting. Analogous effects for I3C-l4N couplings have been reported by Lippmaa and co-workers." However, in their case also a broadening of the I3C lines is found, while the ,lP lines of Figure 2 are only 2-ppm wide. In the absence of the Cu quadrupole interaction and without magic angle spinning, the Cu-P dipolar interaction would result in a more than 3-kHz-wide powder pattern, assuming the Cu-P distance to be 2.3 A.12 In this communication no attempt will be made to explain the unequal splittings together with the absence of severe line broadening. Both theoretical and further experimental work is under way to clarify this point.In another copper complex, (Ph3P)3CuCl, the situtation is different. Here the crystal structure of (Ph3P)3CuC1 indicates that there are three molecules per unit cell, two are crystallographically identical, the third molecule being different." The solid-state 31P N M R spectrum of (Ph3P)3CuC1, Figure 3, shows resonances from the two different molecular sites at +9.9, -2.4, -15.3, and -27.9 ppm and at Also satellite peaks appear on the outer signals. Here the splittings within one quartet are not very different, between 900 and 940 Hz. This indicates a smaller Cu quadrupole interaction as compared to (Ph3P)2CuN03, which is reasonable in view of the higher local symmetry (C3J around Cu in (Ph3P)3CuCl.Of the few known gold cluster compounds the spectrum of one of the more interesting clusters, [ A U~( P P~~)~] [NO3]', is given in Figure 4. The spectrum shows two lines, the low-field one asymmetric, at +48.0 and +68.7 ppm.Because the splitting is too large for a dipolar splitting (for a Au-P distance of 2.3 AIz the rigid lattice dipolar...

Pressure Dependence of the Forward and Backward Rates of 9-tert-Butylanthracene Dewar Isomerization

“…If a thoroughly degassed 9TBA/Zeonex sample is photolyzed and then left in the dark for >24 hours, we found complete recovery of the absorption spectrum.In cyclohexane solution at room temperature, we measured both forward and reverse Dewar reaction dynamics. The forward reaction (9TBA D-9TBA) quantum yield was found to be 6% for 365 nm irradiation, while the reverse reaction rate was measured to be 4.0x10 -5 s -1 , both in good agreement with values previously reported in the literature for similar solvents [23][24][25]. We found the forward rate for the 9TBA D-9TBA reaction to be 1.5x10 -4 s -1 under 2.7 mW/cm 2 365 nm irradiation in a Zeonex matrix under vacuum.…”

The mechanisms of boronate ester formation and fluorescent turn-on in ortho-aminomethylphenylboronic acids

“…6d). Such an internal conversion mechanism is commonly referred to as the loose-bolt effect [103][104][105][106][107] . Just as a loose bolt can absorb energy from a running motor via vibrating and further loosening (or tightening), a high-frequency rotor in resonance with an electronic excited state can absorb energy 108 .…”

Structure Determination of Photoproducts of Anthracenes with (Arylmethoxymethyl) Sidechains

“…[17] Bulky sidechains in 9-position lead to a remarkable valence isomerization (disrotatory [4π] electrocyclic reaction) to "Dewar anthracenes". [18][19][20] Apart from the intramolecular [4π+4π]cycloaddition of anthracene and benzene moieties mentioned above, we found in concentrated solutions of 9,10-disubstituted anthracenes the corresponding intermolecular process. [21] Moreover, anthracenes with special substituents exhibit several further photoreactions.…”