Excited Triplet States of Polyatomic Molecules. II. Flash-Lamp Studies on Aromatic Ketones

Abstract

The apparatus for observing triplet-triplet transitions in polyatomic molecules is the same as in part I except that resonance lamps are here replaced by a flash lamp. Triplet-triplet spectra are reported for benzophenone, acetophenone, β-bromo and β-iodo naphthalene. No triplet-triplet absorption was found in benzene, biacetyl, acetone dibromo benzene, or diisopropyl ketone. Detailed studies of the energy levels of benzophenone and acetophenone are reported.

Reliable Predictions of Benzophenone Singlet–Triplet Transition Rates: A Second-Order Cumulant Approach

“…The FCWDS slightly rises into a short Δ E region between 1200 and 1500 cm –1 because of displaced vibrational coordinates falling in that frequency region, roughly corresponding to the bending and asymmetric stretching involving the carbonyl group and adjacent ring carbons and the stretching of the CO bond. Δ E for the S 1 → T 1 transition can be obtained from the assignments of the 0–0 transitions of the S 1 ← S 0 absorption spectrum and the T 1 → S 0 phosphorescence spectrum, falling at 26 244 and 23 800 cm –1 , respectively. Using such Δ E (2444 cm –1 ) and the computed SOC (28.58 cm –1 , our computation at S 1 minimum-energy geometry), the resulting rate constant for the elementary transition is ≈1 × 10 8 s –1 , with a decay time of the order of nanoseconds, much longer than that found from time-resolved spectroscopic measurements. ,, This situation does not modify by changing the temperature, as shown by the inset of Figure , where the results obtained at different T values are reported.…”

The Triplet State and Molecular Electronic Processes in Organic Molecules

“…Terenin and Ermolaev (393) attribute the green emission to microcrystalline benzophenone; in ethanol, which is a better solvent for benzophenone, they found blue emission only. The emission of crystalline benzophenone was studied by Pesteil and Barbaron (284) and McClure and Hanst (245); the latter authors were able to obtain Pesteil's spectrum in material that had been stored for several weeks after purification, and they suggest that phase transitions between various of the four polymorphic forms of the crystal might be responsible for differences in the crystal spectra. This might also be the origin of the very broad green emission that is commonly observed in some samples of benzophenone, even after extensive purification.…”

Interband transitions in molecular crystals

“…The spectra of this absorption at room temperature (295 + 1 K) and at 77 K are shown in figure 3. The absorption peak at 540 nm is in a similar position to the peak of the T-T absorption for the isolated molecule [4][5][6][7][8]. However, the band is significantly broader, as the peak position and bandwidth summary in the table shows.…”