Triplet excimer emission

Poly[N-(vinyloxy)carbonyl carbazole] has been prepared and found to give rise to two distinct types of triplet excimer emissions while in pure poly(2-vin ylnaphthalene) the 3-dimensional transport theory normally applicable to polystyrene for a spatial periodic lattice did not apply in... 

B.W. D Andrade, J. Brooks, V. Adamovich, M.E. Thompson, and S.R. Forrest, White light emission using triplet excimers in electrophorescent organic light-emitting devices, Adv. Mater., 14 1032-1036 (2002). 

In the pyrene system, the intermediate X has been identified with an excited dimer or excimer, since characteristic excimer emission is also observed. The process of triplet-triplet annihilation then consists of transfer of energy from one triplet to another to form excited dimeric species (S), which dissociates into an excited and a ground state singlets ... 

Besides the prompt excimer emission, delayed excimer emission has been observed. The mechanism is through triplet-triplet annihilation process (Section 5.9B) ... 

Using PMDR methods, the broad excimer emission formed at defect sites in the lattice of hexachlorobenzene crystal at 1.6°K (by doping it with high-energy triplet molecules at 1.6°K) is shown (38) to have zf transitions. This provides strong evidence that it is a triplet excimer. For molecules with atoms having nuclear spin, transitions between hyperfine levels of different zf levels are also observed. 

Triplet excimers of aromatic hydrocarbons have proved very difficult to detect and hence their role in deactivation of excited states is largely speculative. However, on the basis of emission experiments (Subudhi and Lim, 1976 Okajima et al, 1977 Chandra and Lim, 1977 Webster et ai, 1981), it has been suggested that some di(l-naphthyl)alkanes form such species. It is suggested that the favoured conformation of the triplet excimer does not have the two naphthalene rings lying parallel to each other. 

The triplet excimer phosphorescence from liquid solutions of naphthalene and di-2-naphthylalkenes in isooctane previously reported has not been confirmed and the emission probably arose from impurities like biacetyl . Exciton trapping has been studied in doped 1,4-dibromonaphthalene . ENOOR applied to the study of triplet traps of phenanthrene-TCNB in naphthalene-TCNB , and triplet 1- and 2-naphthylphenylcarbenes produced by photolysis of diazo compounds . Conformers of triplet states of 2-naphthaldehyde at 300K , T and T2 states from dual... 

D Andrade B.W., Brooks J., Adamovich V., Thompson M.E., Forrest S.R., "White Light Emission Using Triplet Excimers in Electrophosphorescent Organic Light-Emitting Devices" Advanced Materials, 14,15, August 2002, (1032-1036). 

The fierce dispute over the suggested detection of triplet excimers of naphthalene derivatives continues. Locke and Lin report that in solutions of naphthalene and 1,n-di-a-naphthylalkane the measured emission is definitely not due to biacetyl-like impurities as suggested by other workers in a reinterpretation and re-examination of earlier data. The final decision on the matter is still awaited. 

The luminescence spectra of various polymers and solid model compounds induced by 1 MeV have been compared [200]. An enhanced triplet emission and the absence of fluorescence have been observed for poly(p-xylene) and poly(monochloro-p-xylene). A longer wavelength emission assigned to triplet excimer is reported. Poly(ethylenetereph-thalate) and polysulphone emit primarily from singlet and singlet excimer states. Comparison of electron and UV induced luminescence in these polymers would be very useful for the interpretation of the spectra reported. 

The conditions for probes to be suitable for direct spectroscopic studies have been discussed in Section II.A. The mobility of the probe between two compartments (i.e., the homogenous phase and the complexation site in the supramolecular system) competes with the decay of the excited triplet states in those compartments. This competition is only possible if the probe s excited state lifetime is either very much longer or of the order of magnitude of the rates for association and dissociation from the supramolecular system. Conceptually, the mechanism is analogous to the formation of excimers and the observation of monomer and excimer emission. The solution for the kinetic equations has been described for excimers several decades ago [179] and can be directly applied to the decay for triplet states in the presence of an organized system. This method assumes that at a particular wavelength the molar absorptivity of the free (P) and complexed triplet state (HP) are different. The absorbance is thus related to the sum of the probe concentrations ... 

Pyrene exciplex methods allow key values to be determined over the range of 10 s" to 10 s i. Accurate measur ent of weak pyrene excimer emission is somewhat easier key values down to ca. 3 x 10 s can be determined. Triplet methods are needed to determine cyclization rates in the millisecond domain. 

Triplet states can also be detected by excimer emission, and the study of luminescence transients [3]. 

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