Ultrafast excited-state dynamics of strongly coupled porphyrin/core-substituted-naphthalenediimide dyads

Abstract

The photophysics and excited-state dynamics of two dyads consisting of either a free-base or a zinc-tetraphenylporphyrin linked through a rigid bridge to a core-substituted naphthalenediimide (NDI) have been investigated by femtosecond-resolved spectroscopy. The absorption and fluorescence spectra differ substantially from those of the individual units, pointing to a substantial coupling and to a delocalisation of the excitation over the whole molecule, as confirmed by quantum chemistry calculations. A strong dependence of their excited-state dynamics on the solvent polarity has been observed. In toluene, the fluorescence quantum yield of the dyads is of the order of a few percent and the main decay channel of the emitting state is proposed as intersystem-crossing to the triplet state. However, in a medium polarity solvent like dichloromethane, the emitting state undergoes charge separation from the porphyrin to the NDI unit within 1-3 ps, and the ensuing charge-separated state recombines in about 10-20 ps. This solvent dependence can be explained by the weak driving force for charge separation in polar solvents and the large electronic coupling between the porphyrin and NDI moieties, making charge separation a solvent-controlled adiabatic process.

Electron, Hole, Singlet, and Triplet Energy Transfer in Photoexcited Porphyrin-Naphthalenediimide Dyads

“…The electronic absorption spectra of the dyads in toluene are characterized by an intense band centered around 420 nm, that can be ascribed to the Soret or B band of the porphyrin, and by three weaker bands located at 517, 556, and 601 nm for both 1 and 2 ( Figure 1). These bands are very similar to those observed with HNDI alone, 82 the only difference being a ∼10 nm (310 cm −1 ) blue shift and a narrowing that can be explained by the interaction with the porphyrin (Figure 1). HNDI also exhibits an absorption band in the 400−425 nm region that is, however, much too weak relative to the porphyrin B band to be visible in the dyad spectrum.…”

Multidimensional Attosecond Resonant X-Ray Spectroscopy of Molecules: Lessons from the Optical Regime

“…When paired with recursive optimal control algorithms, it should be possible to control, for example, charge migration or energy-transfer processes (154, 155). …”

Inside Cover: Bioinspired Hierarchical Nanotubular Titania Immobilized with Platinum Nanoparticles for Photocatalytic Hydrogen Production (Chem. Eur. J. 20/2015)

“…In earlier work, we have shown the application of monoannulation for supramolecular self‐assembly,13, 14 selective ion sensing15, 16 and donor–acceptor dyads 12. 19 In this work, we report the synthesis and use of the pyridyl‐monoannulated core‐substituted NDI 1 (Py‐cNDI) for dual applications: firstly its use as a reversible probe for acid sensing, and secondly, the pH‐ and solvent‐controlled assembly of tuneable nanostructures (Figure 1).…”

“…A slight alteration of the core of the naphthalene core by one, two or up to four electron‐donating or ‐withdrawing groups introduces a new electronic transition with charge transfer character located in the visible region 7–9. Core‐substituted naphthalene diimides (cNDIs) have opened new doors for research in the fields of chemistry,10 biology11 and physics12 by combining optical and structural changes to develop functional supramolecular nanostructures13, 14 and ion sensors 15. 16 A pH‐responsive probe based on self‐assembled cNDI derivatives has yet to be reported, although pH‐responsive molecular sensors based on cNDI fluorophores have appeared in the literature 17.…”