European Laboratory for Non Linear Spectroscopy (LENS), Università degli Studi di Firenze, via Nello Carrara 1, 50019 Sesto Fiorentino, Florence, Italy.
Phys Chem Chem Phys. 2018 Aug 29;20(34):22331-22341. doi: 10.1039/c8cp02172d.
The photophysics of 9(19),16(17),23(24)-tri-tert-butyl-2-[ethynyl-(4-carboxymethyl)phenyl]phthalocyaninatozinc(ii) and its H-aggregates is studied in different solvents by means of ultrafast non-linear optical spectroscopy and computational modeling. In non-coordinating solvents, both stationary and time-resolved spectroscopies highlight the formation of extended molecular aggregates, whose dimension and spectral properties depends on the concentration. In all the explored experimental conditions, time-resolved transient absorption experiments show multi exponential decay of the signals. Additional insights into the excited state relaxation mechanisms of the system is obtained with 2D electronic spectroscopy, which is employed to compare the deactivation channels in the absence or presence of aggregates. In ethanol and diethylether, where only monomers are present, an ultrafast relaxation process among the two non-degenerate Q-states of the molecule is evidenced by the appearance of a cross peak in the 2D-maps. In chloroform or CCl4, where disordered H-aggregates are formed, an energy transfer channel among aggregates with different composition and size is observed, leading to the non-radiative decay towards the lower energy dark state of the aggregates. Efficient coupling between less and more aggregated species is highlighted in two-dimensional electronic spectra by the appearance of a cross peak. The kinetics and intensity of the latter depend on the concentration of the solution. Finally, the linear spectroscopic properties of the aggregate are reproduced using a simplified structural model of an extended aggregate, based on Frenkel Hamiltonian Calculations and on an estimate of the electronic couplings between each dimer composing the aggregate computed at DFT level.
通过超快非线性光学光谱学和计算建模研究了 9(19)，16(17)，23(24)-三-叔丁基-2-[乙炔基-(4-羧甲基)苯基]酞菁锌(ii)及其 H-聚集体在不同溶剂中的光物理性质。在非配位溶剂中，稳态和时间分辨光谱都突出了扩展分子聚集体的形成，其尺寸和光谱性质取决于浓度。在所有探索的实验条件下，时间分辨瞬态吸收实验显示信号的多指数衰减。通过二维电子光谱获得了对体系激发态弛豫机制的更多了解，该光谱用于比较在不存在或存在聚集体时的去活通道。在乙醇和二乙醚中，只有单体存在，通过在二维图谱中出现交叉峰，证明了分子两个非简并 Q-态之间存在超快弛豫过程。在氯仿或 CCl4 中，形成无序 H-聚集体，观察到具有不同组成和大小的聚集体之间的能量转移通道，导致向聚集体的较低能量暗态的非辐射衰减。在二维电子光谱中，通过出现交叉峰突出了较少和更多聚集态之间的有效耦合。后者的动力学和强度取决于溶液的浓度。最后，使用基于扩展聚集体的简化结构模型和在 DFT 水平上计算的每个构成聚集体的二聚体之间的电子耦合的估计，重现了聚集体的线性光谱性质。
