Liquid and frozen multilayers of decanol in zeolites as microreactors for direct and oxygen mediated triplet-triplet annihilation of porphyrin

摘要

The kinetics of triplet state decay and concomitant delayed fluorescence of tetraphenylporphyrin(TPP) incorporated into the multilayers of n-decanol adsorbed on the external surface of zeolites at differenttemperatures were studied by the laser flash photolysis via monitoring the emission and diffuse-reflectance.In deoxygenated samples, the kinetics of diffusion-controlled bimolecular triplet-triplet annihilation (TTA)has been used to probe the multilayers. A very large local concentration of reactants may be obtained usingsmall bulk amounts. A fast TTA rate constant demonstrated the triplet energy migration in TPP assembliesformed at the liquid/solid interface. The TTA in aerated samples is mediated by molecular oxygen leadingto1O2feedback—induced delayed fluorescence. Singlet oxygen works as an efficient mobile energy carrierbetween TPP triplets. The parameters of both TTA may be modified by multilayer, which acts as microreactorwith supramolecular organization. The freezing of n-decanol results in dramatic apparent acceleration ofboth direct and1O2mediated TTA due to the increase in local TPP concentration because of displacementof TPP molecules into the residual liquid domains in polycrystalline matrix. The concentration of TPP inthose microreactors can be three orders of magnitude larger than the solubility limit in a particular neatliquid solvent demonstrating the unique features of solid solution, which seems to be due to the presenceof crystal/liquid interfaces.