Intramolecular triplet energy transfer in ester-linked bichromophoric azoalkanes and naphthalenes
作者:Paul S. Engel、Douglas W. Horsey、John N. Scholz、Takashi Karatsu、Akihide Kitamura
DOI:10.1021/j100198a011
日期:1992.9
The photophysics of a series of compounds has been studied wherein a triplet sensitizer such as benzophenone (BB) or thioxanthone (TH) is linked via an ester group to an azoalkane such as 3,3,5,5-tetramethyl-1-pyrazoline (PY) or 2,3-diazabicyclo-[2.2.2]oct-2-ene (DBO). The observation of phosphorescence from the sensitizer moiety in a frozen glass and triplet lifetime measurements in solution show that intramolecular triplet energy transfer (ET) can be remarkably slow. Model compounds in which naphthalene replaces the azo group behave normally, exhibiting complete and rapid intramolecular ET. Despite the small size of the azo group, its critical radius, R0, for intermolecular ET in a frozen glass is comparable to that of naphthalene. When the donor and azo chromophores are closely linked by alkyl groups, ET is very rapid. No phosphorescence or T-T absorption of the azo group could be detected, but quenching experiments show that the triplet lifetime of cyclic azoalkanes is much shorter than their singlet lifetime.