Directional charge separation in isolated organic semiconductor crystalline nanowires

Abstract

One of the fundamental design paradigms in organic photovoltaic device engineering is based on the idea that charge separation is an extrinsically driven process requiring an interface for exciton fission. This idea has driven an enormous materials science engineering effort focused on construction of domain sizes commensurate with a nominal exciton diffusion length of order 10 nm. Here, we show that polarized optical excitation of isolated pristine crystalline nanowires of a small molecule n-type organic semiconductor, 7,8,15,16-tetraazaterrylene, generates a significant population of charge-separated polaron pairs along the π-stacking direction. Charge separation was signalled by pronounced power-law photoluminescence decay polarized along the same axis. In the transverse direction, we observed exponential decay associated with excitons localized on individual monomers. We propose that this effect derives from an intrinsic directional charge-transfer interaction that can ultimately be programmed by molecular packing geometry.

Role of Ionic Functional Groups on Ion Transport at Perovskite Interfaces

“…In contrast, the PVBT-SB interlayer displayed a pronounced power-law decay, indicative of a two-body recombination of dilute polaron pairs. [52][53] . The power-law decay (see equation in figure caption of Figure S15) is characterized by the decay constant (.…”

Mesomorphic Behavior in Silver(I) N-(4-Pyridyl) Benzamide with Aromatic π–π Stacking Counterions

“…Engineering new materials with directional non-covalent interactions is a rapidly growing area [ 10 , 11 , 12 , 13 ], with the potential to generate novel molecular architectures using hydrogen bonding [ 14 ], metal–ligand coordination [ 15 , 16 ], and π–π stacking interactions [ 17 , 18 , 19 , 20 , 21 , 22 ]. In particular, aromatic π–π stacking interactions can direct the formation of one-dimensional (1D), 2D, and 3D crystalline nanostructures through self-assembly [ 23 , 24 ] and they can serve to engineer the physical properties of organic semiconductors [ 25 , 26 , 27 , 28 , 29 ]. With regard to intermolecular interactions, other factors such as solvents [ 30 , 31 , 32 , 33 , 34 ] and counterions [ 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 ] have been shown to play key roles in the structure of the final assembly.…”

Disentangling “Bright” and “Dark” Interactions in Ordered Assemblies of Organic Semiconductors

“…In the HJ aggregate model developed by Spano and co-workers, the usual Holstein Hamiltonian describing Frenkel exciton (FE) coupling via dipole–dipole interaction is augmented with short-range CT interactions as well as FE-CT mixing terms. , The CT interaction is defined by two terms: the hole ⟨ t h ⟩ and electron ⟨ t e ⟩ transfer integrals that describe the energy associated with transfer of hole/electron between adjacent molecules, and they are linked with the CT coupling energy by the second order perturbation theory. ,, Because this interaction requires wave function overlap, both ⟨ t e ⟩ and ⟨ t h ⟩ are short-range interactions (acting over a distance of ∼3.5 Å) and are exquisitely sensitive (in sign and magnitude) to sub-Å atomic registration displacements between molecules. − In the ground state, the coupled electronic wave function interaction is described by ⟨ t h ⟩ with an energy bandwidth of ∼4 |⟨ t h ⟩|; if each individual molecule is a charge-neutral singlet, then each state in the ground state band is filled, and the valence band maximum is ∼2 |⟨ t h ⟩|. In the general case of organic semiconductors where the coupling is strongest along the pi-stacking direction, it becomes difficult, if not impossible, to parse the different coupling modes (FE vs CT) by photoluminescence (PL) methods alone.…”

“…In the present study, we used 7,8,15,16-tetraazaterrylene (TAT), a nitrogen-substituted terrylene system that functions as an n-type semiconductor . TAT readily forms crystalline aggregates from either physical vapor transport , or solution-based self-assembly . TAT has a number of interesting and important properties useful for the interrogation of (packing) structure correlated electronic properties: First and foremost, TAT aggregates are highly photostable, and its vibronic structure is preserved upon aggregation where the intensity profile encodes information on packing structure and pi-stacking order.…”

“…9,10 The CT interaction is defined by two terms: the hole ⟨t h ⟩ and electron ⟨t e ⟩ transfer integrals that describe the energy associated with transfer of hole/electron between adjacent molecules, and they are linked with the CT coupling energy by the second order perturbation theory. 8,11,12 Because this interaction requires wave function overlap, both ⟨t e ⟩ and ⟨t h ⟩ are short-range interactions (acting over a distance of ∼3.5 Å) and are exquisitely sensitive (in sign and magnitude) to sub-Å atomic registration displacements between molecules. 6−9 In the ground state, the coupled electronic wave function interaction is described by ⟨t h ⟩ with an energy bandwidth of ∼4 |⟨t h ⟩|; if each individual molecule is a chargeneutral singlet, then each state in the ground state band is filled, and the valence band maximum is ∼2 |⟨t h ⟩|.…”