Singlet molecular oxygen annihilation luminescence in polymers

Abstract

In this investigation, we characterize three types of oxygen stimulated emission from organic chromophores embedded in polymer matrices: (i) singlet oxygen annihilation fluorescence from the S₁ state of the chromophore; (ii) specific sensitization of excimer fluorescence in the stimulated emission; and (iii) oxciplex emission. The oxciplex emissions are the first reported examples of emissions originating from transitions within an organic molecule–singlet oxygen complex. To summarize the spectral analysis, the major emitting transition in singlet oxygen annihilation luminescence is the most radiative transition of either the organic chromophore or the oxygen–organic chromophore complex, which is of equal or of lower energy than [E₀₂(¹Δ)+E_T1]. A kinetic analysis shows that the behavior of the annihilation fluorescence resembles triplet–triplet annihilation fluorescence. In this case, however, the dependence of the kinetics on the organic triplet population varies with the ability of singlet oxygen to participate in sequential collisional energy transfer to adjacent ground state oxygen molecules, minimizing the necessity for physical diffusion of singlet oxygen through the matrix. The kinetic behavior of the annihilation fluorescence can be understood in terms of the diffusion of an energy packet, an oxciton, composed of the electronic excitation energy of O₂(¹Δ) through the polymer matrix, hopping from one oxygen molecule to the next.