J-type nanosized-aggregates (NA) of zinc and platinum-octaethylporphyrin (ZnOEP and PtOEP) are prepared and observed to undergo fast triplet formation via inter system crossing (ISC) process. The ultrafast transient absorption measurement of ZnOEP NA indicates fast decay of singlet excitonic state with the lifetime of ∼9 ps. On other hand, the singlet decay rate is even faster for PtOEP NA, having lifetime value of ∼0.8 ps. Singlet excitonic decays cause subsequent population of triplet states which possess long annihilation free lifetimes of 1.7 and 0.6 ms for ZnOEP and PtOEP NA, respectively. However, at high exciton densities the triplet excitons are observed to decay via triplet-triplet annihilation (TTA) and their natural radiative, non-radiative decay processes. The exciton density dependent triplet decay dynamics further analyzed to estimate TTA rate constants and exciton diffusion parameters. The triplet exciton diffusion coefficient values thus obtained are 4.06 × 10⁻⁷ and 0.94 × 10⁻⁷ cm² s^-1 for ZnOEP and PtOEP NAs, respectively. The diffusion coefficients possess nearly two order smaller values as compared to those of the commonly reported singlet excitons. Involvement of spin exchange based short range transfer mechanism of triplet exciton make this diffusion process slower. However, the possible involvement of singlet-triplet cooperative diffusion mechanism results ∼4.3 time faster triplet diffusion in ZnOEP NAs as compared to that of the PtOEP NAs. The slow exciton diffusion properties of triplet enhance the importance of requirement of long triplet lifetime to obtain an elongated triplet diffusion length. These two nanoparticles are observed to fulfill the long lifetime criteria and own reasonably long triplet diffusion lengths which may be beneficial for solar cell, photon up-conversion and singlet oxygen generation based applications.

制备锌和铂-八乙基卟啉（ZnOEP和PtOEP）的J型纳米聚集体（NA），并通过系统间交叉（ISC）过程观察到快速形成三重态。ZnOEP NA的超快速瞬态吸收测量表明，单线态激子态快速衰减，寿命约为9 ps。另一方面，PtOEP NA的单重态衰减速率甚至更快，寿命值为〜0.8 ps。单重态激子衰变会导致随后的三重态填充，对于ZnOEP和PtOEP NA，它们的无an灭寿命较长，分别为1.7和0.6 ms。然而，在高激子密度下，观察到三重态激子会通过三重态-三重态an灭（TTA）及其自然辐射，非辐射衰变过程而衰变。激子密度相关的三重态衰变动力学进一步分析以估计TTA速率常数和激子扩散参数。由此获得的三重态激子扩散系数值为4.06×10^-7和0.94×10 ^-7 cm ² s ^-1分别用于ZnOEP和PtOEP NA。与通常报道的单线态激子相比，扩散系数的值几乎减小了两个数量级。基于自旋交换的三重态激子的短程转移机制的介入使该扩散过程变慢。然而，与PtOEP NAs相比，可能存在的单重态-三重态协同扩散机制导致ZnOEP NAs的三重态扩散快约4.3倍。三重态的慢激子扩散性质提高了要求长三重态寿命以获得延长的三重态扩散长度的重要性。观察到这两种纳米粒子符合长寿命标准，并具有相当长的三重态扩散长度，这可能对太阳能电池有利，