Reversible intersystem crossing, fluorescence lifetime lengthening and collisionally induced phosphorescence in biacetyl
✍ Scribed by Renie Van Der Werf; Dick Zevenhuijzen; Jan Kommandeur
- Publisher
- Elsevier Science
- Year
- 1974
- Tongue
- English
- Weight
- 540 KB
- Volume
- 27
- Category
- Article
- ISSN
- 0009-2614
No coin nor oath required. For personal study only.
✦ Synopsis
The emissions of biacetyl excited at 4200 19 were studied at pressures down to 10m3 torr. Apart from the wellknown nanosecond fluorescence, a new emission of the same spectral composition was found with a non-exponential decay in the microsecond range. Furthermore the phosphorescence, as defined by its spectral composition, was found to be collisionally induced. The results imply that after excitation, the molecule rapidly transfers (rate constant kS_T) to the triplet state, giving rise to the nanosecond decay time; and can then transfer back to the singlet state (rate constant kT+S), giving rise to the microsecond emission. At the same time internal conversion can occur (LS+o).
From an analysis of the data we find for AS+So = 2.4 X lo7 set-' , /CS_T = 7.6 X lo7 see-' , kT+s = 1.9 X 10' set-' The kinetic treatment can be transformed to a quantum mechanical one, yielding values for the triplet level density (pT), the coupling element VST and the number of triplet states (N) coupled to the singlet excited. At 4200 A we find PT = 6.3 X 10' cm, VST=l.OX 10-scm-1,N=400. Phosphorescence occurs only when the molecule is deactivated by collisions to a vibronic triplet state below the vibrationless excited singlet state. The efficiency of biacetyl collisions is 0.54.