Dear Ashkan Karimi ,

There are two main ways to determine the position of the triplet level - theoretical and experimental

If the compound does not phosphoresce at room temperature, it is necessary to prepare a glass-forming solution of this compound and, using a thermostat, to record the phosphorescence spectrum at low temperature close to 77 K. If it is possible to register the absorption spectrum, then the point of intersection of the normalized absorption and emission spectra will give the position of the S1 singlet level. The T1 triplet level has a lower energy, and its position can be estimated from the position of the longer-term maximum in the emission spectrum, which is formed by overlapping fluorescence and phosphorescence spectra. Most organic compounds in the glassy medium have a sufficiently long phosphorescence lifetime, and the phosphorescence decay can be observed visually, interrupting the exciting light with a shroud, or even by hand.

As a solvent, special glass-forming mixtures of alcohols and other solvents are used. For primary experiments, isobutyl alcohol is an excellent solvent. Ethyl alcohol is highly cracked and will certainly lead to the destruction of the cuvette. Therefore, for qualitative experiments, polymeric or quartz glass cuvettes are used.

Triplet-triplet absoprtion as a transient with a lifetime longer than fluorescence or delayed fluorescence

Unfortunately, triplet-triplet absorption does not make it possible to determine the position of the T1-level. This is a misconception.

Dear Prof. Pavlovich,

Thanks for your comprehensive explanation and kind reply.

dr Pavlovich

You are right

First I misread the question: I thought it was about the lifetime

T-T absorption indeed does not give the T1 state but it can be used as a check for the calculations of the energr diferences in the triplet-manifold and thus on the precision of the calculation

Endergonic triplet energy transfer from a known reference -complications may occur.

Endergonic triplet energy transfer from a known reference -complications may occur. - A permissible fantasy that will never be used in practice.

During the early seventies, I have found that the kinetic formulation of the triplet excimers that was based on log 1/t(phos or delflu)vs 1/T plots in solution were not correct but the very idea was good - later I was corroborated by others. I prepared a very pure solvent to test the energy transfer between phenanthrene and naphthalene. The very brief flash photolysis measurement revealed energy transfers in both direction, with a difference in rates corresponding to E3ph - E3na. An earlier interpretation of this quenching turned out to be incorrect ,also. I might publish a brief note. This approach served to locate the triplet energy of azulene, and to discover the S2 delayed fluorescence emission rejected by The Chem. Phys in the seventies. The triplet absorption and the S2 delayed fluorescence emission have later been corroborated by others. The problem was that in the acknowledgement I expressed my displeasure to the well organized activity of hatred toward my work and me .I refused to sell (for free) to a professor the absolute right to my discovery of the versatile and efficient production of transient radical ions from triplet ar. ketone + dabco and refused to swore in to an other professor to keep my bad experiences a secret - hoped to share that discovery with both of them in exchange for protection of my work from hatred, sabotage and even a organized destruction by the Chem. Dep. M.Toth