Energy transfer 4,4 -BPDC

Energy Transfer Studies with Dimethyl Terephthalate (DMT) and 4,4 -BPDC. Several attempts were made to determine if energy transfer could occur from an excited DMT molecule to a 4,4 -BPDC molecule in a rigid ethanol glass at 77°K. These studies were accomplished by adding various amounts (20 - 50 mole percent) 4,4 -BPDC to a known concentration (5.0 x 10"4 M) of DMT. The change in emission intensity at 418 nm, which is exclusively emission from DMT, was then measured with excitation at 298 nm. 

In addition, it can be shown for the concentration range of the 4,4 -BPDC used, assuming each molecule occupies a spherical volume, the average radius of this volume is about 108 a. This calculation predicts, on the average, the probability of an excited DMT molecule having a 4,4 -BPDC molecule within the required 15 A for energy transfer to occur by the exchange mechanism, which would be spin allowed, is small. 

If neither mode of energy transfer is acceptable, a different explanation of the apparent quenching of the DMT phosphorescence must be put forth. It must be recalled that both DMT and 4,4 -BPDC absorb 298 nm light, which introduces the argument that competitive absorption causes the apparent quenching effect. 

The conclusion from the monomer solvent studies is that, in nearly equal molar solutions, DMT and 4,4 -BPDC compete for absorption of the 298 nm radiation. However, the results also show that, even in equal concentrations, the DMT emission, when excited by 298 nm light, is several times as intense as the 4,4 -BPDC emission at 472 nm. It must be emphasized that these studies do not preclude the existence of energy transfer from excited DMT to 4,4 -BPDC. From the volume calculation used above, it can be shown that a concentration of v 0.1 M 4,4 -BPDC is needed to assume an occupied volume with radius of 15 8, the required distance for the exchange mechanism. 

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See also in sourсe #XX -- [ ]

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