Triplet—Triplet Annihilation and Delayed Fluorescence in Molecular Aggregates
Triplet-triplet annihiiation in pure and mixed organic crystals is discussed. In crystals containing a small concentration of impurity traps, triplet excitation migration may proceed from trap to trap on a time scale that is short compared with the long triplet state lifetime but that is long compared with the normal fluorescence lifetime. Nearest-neighbor and long-range mutual annihilation of bvo triplets may then take place giving rise to delayed fluorescence. The rates of long-range triplet excitation migration and annihilation show a concentration dependence, temperature dependence, and solvent dependence. Provided the triplet-triplet annihilation rate is not too fast, the intensity of the delayed fluorescence can be shown to depend upon the square of the intensity of the exciting light. This expectation is borne out by experiments, briefly reported, on delayed fluorescence in dilute isotopic mixed crystals. In crystals containing high concentrations of such impurity traps, or in pure crystals, the annihilation rate becomes extremely rapid and the mechanism effectively quenches phosphorescence in many, but not all, classes of pure organic crystals. The kinetics of the over-all process are discussed in both the limits of fast and slow annihilation rates. A theoretical investigation of the origin of the annihilation matrix element was carried out, and it is shown that exchange interactions play the largest role in determining annihilation rates. (P.C.H.)
- Research Organization:
- California Inst. of Tech., Pasadena
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-17-031112
- OSTI ID:
- 4672702
- Journal Information:
- Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 6 Vol. 38; ISSN JCPSA6; ISSN 0021-9606
- Publisher:
- American Institute of Physics (AIP)
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
Similar Records
Delayed Luminescence of Organic Mixed Crystals. VI. Delayed Excimer Fluorescence of Pyrene in Biphenyl
Photoassociation and photoinduced charge transfer in bridged diaryl compounds. 6. Intramolecular triplet excimers of dicarbazolylalkanes and their comparison to an intermolecular triplet excimer of carbazole