The meso-tetrakis (methylpyridiniumyl) porphyrin complexed with Fe³⁺ (Fe³⁺TMPyP) is an irregular porphyrin, possessing unfilled d external shells with d⁶ electronic configuration. In aqueous solution, Fe³⁺TMPyP exists in a complex equilibrium of different forms. Changing the solution pH, these complexes can bind to other species (as OH- and H₂O) or form physical aggregates (μ-oxo-dimers), that alter their excited states properties and affect their potential applications. In the present work, we report excited state absorption dynamics of Fe³⁺TMPyP molecular complexes in different pH employing femtosecond Z-Scan and ultrafast transient absorption techniques. Complementary data were obtained by UV–vis absorption and fluorescence emission spectroscopies. For 532 nm excitation, the Z-Scan technique shows a decrease in the absorption coefficient for Fe³⁺TMPyP at pH 4.0 and an increase at pHs 7.0 and 9.0. Ultrafast transient absorption reveals the same behavior in the 525−570 nm region for samples at pHs 7.0 and 9.0. Fast relaxations, with lifetimes around 2.0 picoseconds, were obtained for all samples studied, and were attributed to internal conversion relaxation processes. Although the molecular aggregation accelerates the relaxation process of regular porphyrins, μ-oxo-dimers slightly affect the relaxation of Fe³⁺TMPyP. The prompt conversion of absorbed light energy in heat observed to Fe³⁺TMPyP porphyrins can be useful for biomedical photothermal applications, such as Photoacoustic Imaging (PAI) and Photothermal Therapy (PTT).

的内消旋与铁络合四（methylpyridiniumyl）卟啉³⁺（FE ³⁺ TMPyP）是不规则的卟啉，具有未填充的d外部壳与d ⁶电子配置。在水溶液中，Fe ³⁺ TMPyP以不同形式的复杂平衡存在。改变溶液的pH值，这些络合物可以与其他物质结合（如OH-和H ₂ O）或形成物理聚集体（μ-氧代二聚体），从而改变其激发态性质并影响其潜在应用。在本工作中，我们报告了Fe ^3+的激发态吸收动力学使用飞秒Z扫描和超快速瞬态吸收技术在不同pH值下的TMPyP分子复合物。通过紫外可见吸收光谱和荧光发射光谱学获得了补充数据。对于532 nm激发，Z-Scan技术显示在pH 4.0下Fe ³⁺ TMPyP的吸收系数降低，在pH 7.0和9.0下增加。对于pH 7.0和9.0的样品，超快瞬态吸收揭示了在525-570 nm区域内的相同行为。所有研究样品均获得快速松弛，寿命约为2.0皮秒，这归因于内部转化松弛过程。尽管分子聚集加速了常规卟啉的弛豫过程，但μ-氧代二聚体对Fe ³⁺的弛豫有轻微影响TMPyP。将观察到的热中的吸收光能迅速转换为Fe ³⁺ TMPyP卟啉可用于生物医学光热应用，例如光声成像（PAI）和光热疗法（PTT）。