The influence of deuteration of complex organic molecules on their fluorescence quantum yield (a review)

Data on the influence of deuteration of organic molecules and/or solvent on their fluorescence quantum yield are summarized. It is demonstrated that the effect of deuteration is normal, i.e., deuteration increases the fluorescence quantum yield due to decrease in the internal conversion probability, for organic molecules exhibiting fluorescence in the red region of spectrum, in which the internal conversion competes with the emission of fluorescence. In the case in which the probability of internal conversion is low, i.e., energy of level S1 ≥ 16000–20000 cm–1, the intersystem crossing probability from the S1 state to the set of triplet levels depends on the relative position of S1 and the nearest triplet level. In so doing, the effect of deuteration can be either normal or anomalous, depending on whether the resonance between the S1 level and the level nearest to it, the Tn level, improves or deteriorates when these levels shift as a result of deuteration. In dilute vapors, cooled supersonic jets, and crystalline matrices, including Shpolskii matrices, the effect of deuteration at helium temperatures depends on exact resonance between the interacting levels. In the case of dilute vapors and cooled jets, the effect also depends on the vibronic level being excited. Deuteration of OH and NH groups, as a rule, slows proton transfer in the S1 state of the molecule that occurs with their involvement, leading to normal effect of deuteration.