Comparison of Charge-Transfer Dynamics of Naphthalenediimide Triads in Solution and π-Stack Architectures on Solid Surfaces

Abstract

The femto- to microsecond excited-state dynamics of an electron donor–acceptor–donor triad, consisting of two red core-substituted naphthalenediimides (rNDI) and one colorless naphthalenediimide (pNDI), in solution has been compared to that of a supramolecular surface architecture, constituted of coaxial stacks of rNDI and pNDI and prepared by self-organizing surface initiated polymerization (SOSIP). In the triad, charge separation between an excited rNDI and pNDI takes place in highly polar solvents only and for a subensemble of molecules, around 30%, with a folded conformation. Other processes, such as singlet and triplet excitation energy transfer from pNDI to rNDI and intersystem crossing, are also operative. Additionally, bimolecular symmetry-breaking charge separation upon triplet–triplet annihilation is observed on the microsecond time scale in polar solvent. In the surface architecture, excitation of an rNDI is followed by an ultrafast symmetry breaking-charge separation resulting in a charge-transfer exciton, which either recombines or dissociates into a charge-separated state with the electron and the hole in different stacks. The same charge-separated state can also be populated upon excitation of pNDI, either via a charge-transfer pNDI exciton or after excitation energy transfer to rNDI. Charge recombination in the SOSIP film takes place on a wide range of time scales, ranging from a few picoseconds to several hundreds of microseconds

A Dynamic View of Proton-Coupled Electron Transfer in Photocatalytic Water Splitting

“…The potential problem of charge recombination can be also alleviated by inserting appropriate molecular bridge units with rectifying properties between the dye and the semiconductor 16,59,80,81 or by engineering n/p-supramolecular heterojunctions. [45][46][47][48] We will no further address this point in this work and assume a long-lived oxidized state.…”

“…44 Furthermore, they allow the construction of n/p-supramolecular heterojunctions presenting antiparallel gradients in electron and holes channels to achieve photoinduced long-distance charge separation and reduce charge recombination. [45][46][47][48] Scheme 1. Schematic representation of the proposed photoanode (1) including the acceptorsemiconductor (TiO 2 ), the molecular chromophore NDI 1 , and the Ru-based water oxidation catalyst; (1a) chromophore-semiconductor subsystem employed for the photoinduced electron injection simulation; (1b) chromophore-catalyst subsystem used in the simulation of the first water oxidation catalytic step.…”

Tunable Twisting Motion of Organic Linkers via Concentration and Hydrogen-Bond Formation

“…21 To significantly suppress such non-radiative twisting motions and subsequently enhance the fluorescence quantum yields of such organic molecules, several chemical and material approaches have been established and developed, such as forming aggregation/suspensions at relatively high concentration in the presence of solvent mixtures, producing solid-state forms, constructing thinfilms, incorporating heavy metal atoms, and embedding them in polymer chains. [15][16][32][33] Nevertheless, these new approaches can induce other nonradiative processes, such as energy transfer, charge transfer, and defect states, that lead to different deactivation pathways of the excited state of the targeted molecules. 1,11,18,30,[34][35][36][37][38][39][40][41][42][43][44][45][46][47] In this paper, we show for the first time that relatively low concentrations (nano-to micromolar scale) of a soluble organic linker with double carboxylic groups can form distinct species with different emission peaks, different excited state lifetimes, and exceptionally high PLQYs.…”

Dipolar Photosystems: Engineering Oriented Push–Pull Components into Double‐ and Triple‐Channel Surface Architectures

“…Most importantly, covalent face‐to‐face API dimers have been shown to undergo symmetry breaking charge separation . This process was identified as important to achieve efficient interchannel charge separation in SOSIP . As far as fundamental properties are concerned, APIs excel with strong absorbance in the visible range, HOMO–LUMO energy levels that are compatible with NDIs as n transporters, and strong dipole moments in the ground (∼5 D) and the S 1 excited state (∼20 D)…”

“…[3b] This process was identified as important to achieve efficient interchannel charge separation in SOSIP. [16] As far as fundamentalp roperties are concerned, APIs excel with strong absorbance in the visible range, HOMO-LUMO energy levels that are compatible with NDIs as nt ransporters, and strong dipole moments in the ground (~5D)a nd the S 1 excited state (~20 D). [3] Smaller homologs of APIs, aminonaphthalimides (ANIs), [4,17] retain most of the favorable properties described above with al arger band gap.…”