trans-[Pt­(bodipy)­(N3)­(PEt3)2] (bodipy = 4,4-difluoro-4-bora-3a,4a-diaza-s-indacen-8-yl; Et = ethyl) reacts with dimethyl acetylenedicarboxylate (DMAD) or F3C–CC–COOEt in a catalyst-free room-temperature iClick reaction to provide the complexes [Pt­(bodipy)­(triazolateR,R′)­(PEt3)2] with R = R′ = COOCH3 or R = CF3, R′ = COOEt. The main product is the N2-coordinated triazolate, but some minor signals point to an additional N1 species as well as some trans → cis isomerization of the Pt­(PEt3)2 moiety. Kinetic studies with 1H, 19F, and 31P NMR spectroscopy gave second-order rate constants k 2 in the range of (2.5–6.0) × 10–3 M–1 s–1, with the CF3-substituted alkyne reacting faster than DMAD. Upon photoexcitation, the parent azido complex as well as the two triazolate products exhibit considerable efficiency in the triplet-state population. Notably, the efficiency of intersystem crossing was modulated by the iClick reaction, which was also studied by density functional theory calculations.

Herein, we present a new method to efficiently calculate electronically excited states in large molecular assemblies, consisting of hundreds of molecules. For this purpose, we combine the long-range corrected tight-binding density-functional fragment molecular orbital method (FMO-LC-DFTB) with an excitonic Hamiltonian, which is constructed in the basis of locally excited and charge-transfer configuration state functions calculated for embedded monomers and dimers and accounts explicitly for the electronic coupling between all types of excitons. We first evaluate both the accuracy and efficiency of our fragmentation approach for molecular dimers and aggregates by comparing with the full LC-TD-DFTB method. The comparison of the calculated spectra of an anthracene cluster shows a very good agreement between our method and the LC-TD-DFTB reference. The effective computational scaling of our method has been explored for anthracene clusters and for perylene bisimide aggregates. We demonstrate the applicability of our method by the calculation of the excited state properties of pentacene crystal models consisting of up to 319 molecules. Furthermore, the participation ratio of the monomer fragments to the excited states is analyzed by the calculation of natural transition orbital (NTO) participation numbers, which are verified by the hole and particle density for a chosen pentacene cluster. The use of our FMO-LC-TDDFTB method will allow for future studies of excitonic dynamics and charge transport to be performed on complex molecular systems consisting of thousands of atoms.

We investigate the validity of the classical approximation to the numerically exact quantum dynamics for infrared laser-driven control of isomerization processes. To this end, we simulate the fully quantum mechanical dynamics both by wavepacket propagation in position space and by propagating the Wigner function in phase space employing a quantum-mechanical correction term. A systematic comparison is made with purely classical propagation of the Wigner function. On the example of a one-dimensional double well potential, we identify two complementary classes of pulse sequences that invoke either a quantum mechanically or a classically dominated control mechanism. The quantum control relies on a sequence of excitations and de-excitations between the system’s eigenstates on a time scale far exceeding the characteristic vibrational oscillation periods. In contrast, the classical control mechanism is based on a short and strong few-cycle field exerting classical-like forces driving the wavepacket to the target potential well where it is slowed down and finally trapped. While in the first case, only the quantum mechanical propagation correctly describes the field-induced population transfer, the short pulse case is also amenable to a purely classical description. These findings shed light on the applicability of classical approximations to simulate laser-controlled dynamics and may offer a guideline for novel control experiments in more complex systems that can be analyzed and interpreted utilizing efficient state-of-the-art classical trajectory simulations based on ab initio molecular dynamics.

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