Kim Dabin, Ravotto Luca, Bialas April, Troxler Thomas, Ou Zhongping, Kadish Karl M, Cheprakov Andrei V, Spano Frank C, Vinogradov Sergei A, Anna Jessica M
Department of Chemistry, School of Arts and Sciences, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
J Phys Chem B. 2025 Oct 2;129(39):10049-10062. doi: 10.1021/acs.jpcb.5c03312. Epub 2025 Jun 13.
Dipyrrins form a group of versatile chromophores, which find use as laser dyes as well as in light harvesting and bioimaging applications. The mode of the central ion coordination and the ensuing molecular geometry play a key role in the photophysics of dipyrrins, whereby some complexes are brightly fluorescent and some completely lack emissivity. However, the relationship between the structure and excitation dynamics in dipyrrins is still poorly understood. Here, we used a range of spectroscopic methods to investigate the photophysics of Zn(II) complexes of -Ar-2,2'-di--butoxycarbonyl-dibenzodipyrrins (BDP; Ar = 4-MeOC-CH). In particular, two-dimensional electronic spectroscopy (2DES) was used to characterize the initial excited states in a homoleptic -dipyrrinate Zn(BDP), in which two dipyrrin ligands are oriented in a nonorthogonal geometry. From the position of the peaks in the 2DES spectra and spectral modeling, the initial excited states of Zn(BDP) were assigned to excitonic states. The low oscillator strength, associated with excitation to the lower excitonic state, is responsible in part for the weak emissivity of Zn(BDP), contrasting the bright fluorescence of -dippyrinate Zn(BDP)X. Femtosecond (fs-), nanosecond (ns-) transient absorption (TA), and time-resolved fluorescence spectroscopies were used to monitor the solvent-dependent evolution of the excitonic states, which appear to evolve into an intermediate state possibly with charge transfer character. Taken together, our findings reveal a significant impact of both structural and environmental factors on the photophysics of dipyrrins and present the first example of the application of 2DES to investigate excitonic states in a system where the interacting chromophores are held together via coordination of an optically neutral metal ion. On a broader scale, we demonstrate that nonorthogonal -dipyrrin complexes constitute a versatile model for studying exciton coupling and associated energy and charge dynamics.
二吡咯类化合物构成了一类多功能发色团，它们被用作激光染料以及用于光捕获和生物成像应用。中心离子配位模式及随之产生的分子几何结构在二吡咯类化合物的光物理过程中起着关键作用，据此一些配合物具有明亮的荧光，而一些则完全没有发射率。然而，二吡咯类化合物的结构与激发动力学之间的关系仍知之甚少。在此，我们使用了一系列光谱方法来研究 -Ar-2,2'-二-丁氧基羰基-二苯并二吡咯（BDP；Ar = 4-MeOC-CH）的锌（II）配合物的光物理性质。特别地，二维电子光谱（2DES）被用于表征同配体 -二吡咯锌（BDP）中的初始激发态，其中两个二吡咯配体以非正交几何结构排列。根据2DES光谱中峰的位置和光谱建模，锌（BDP）的初始激发态被指定为激子态。与激发到较低激子态相关的低振子强度部分导致了锌（BDP）的弱发射率，这与 -二吡咯锌（BDP）X的明亮荧光形成对比。飞秒（fs-）、纳秒（ns-）瞬态吸收（TA）和时间分辨荧光光谱被用于监测激子态的溶剂依赖性演化，这些激子态似乎演变成一种可能具有电荷转移特征的中间态。综上所述，我们的研究结果揭示了结构和环境因素对二吡咯类化合物光物理性质的重大影响，并展示了2DES在研究通过光学中性金属离子配位将相互作用的发色团结合在一起的系统中的激子态时的首个应用实例。在更广泛的范围内，我们证明非正交 -二吡咯配合物构成了研究激子耦合以及相关能量和电荷动力学的通用模型。
