Sulfur-Bridged Terthiophene Dimers: How Sulfur Oxidation State Controls Interchromophore Electronic Coupling

Abstract

Symmetric dimers have the potential to optimize energy transfer and charge separation in optoelectronic devices. In this paper, a combination of optical spectroscopy (steady-state and time-resolved) and electronic structure theory is used to analyze the photophysics of sulfur-bridged terthiophene dimers. This class of dimers has the unique feature that the interchromophore (intradimer) electronic coupling can be modified by varying the oxidation state of the bridging sulfur from sulfide (S), to sulfoxide (SO), to sulfone (SO2). Photoexcitation leads to the formation of a delocalized charge resonance state (S1) that relaxes quickly (<10 ps) to a charge-transfer state (S1*). The amount of charge-transfer character in S1* can be enhanced by increasing the oxidation state of the bridging sulfur group as well as the solvent polarity. The S1* state has a decreased intersystem crossing rate when compared to monomeric terthiophene, leading to an enhanced photoluminescence quantum yield. Computational results indicate that electrostatic screening by the bridging sulfur electrons is the key parameter that controls the amount of charge-transfer character. Control of the sulfur bridge oxidation state provides the ability to tune interchromophore interactions in covalent assemblies without altering the molecular geometry or solvent polarity. This capability provides a new strategy for the design of functional supermolecules with applications in organic electronics.

The photophysics of naphthalene dimers controlled by sulfur bridge oxidation

“…This trend can be attributed to the electronic screening by the sulfur electron lone-pairs, which limits the interactions between the two sets of π-electrons, as recently discussed in sulfur-bridged terthiophene dimers. 10 On the other hand, the LE/CT B couplings are much larger in the sulfide than in the sulfoxide bridge in accordance with the amount of CT B in the excitation, which can be rationalized as a result of the presence of one additional electron lone-pair in the former.…”

“… 9 This trend was later scrutinized in the case of terthiophene dimers. 10 The study concluded that rapid intersystem crossing (ISC) to the triplet state manifold is the main deactivation process limiting the fluorescence quantum yield, as observed in pristine terthiophene. 11 , 12 The ISC efficiency is reduced in the presence of intramolecular charge transfer (CT), which can be tuned by the oxidation state of the bridging sulfur group.…”

Controllable Electronic Structures and Photoinduced Processes of Bay‐Linked Perylenediimide Dimers and a Ferrocene‐Linked Triad

“…From these results, the degree of electronic coupling follows the order (PDI) 2 > p ‐(PDI) 2 ≈ m ‐(PDI) 2 . To further examine the origins of the Davydov splitting, the relative energy differences Δ E in the transition band were theoretically calculated according to a reported method . The detailed calculation processes are shown in the Supporting Information, Table S3.…”

“…From these results, the degree of electronic coupling follows the order (PDI) 2 > p-(PDI) 2 % m-(PDI) 2 .T of urther examinet he origins of the Davydovs plitting, the relative energy differences DE in the transition band were theoretically calculated according to ar eportedm ethod. [23] The detailed calculation processes are shown in the Supporting Information, Ta ble S3. Briefly,t he DE values weree stimated to be (PDI) 2 :1 9cm À1 , p-(PDI) 2 : 16 cm À1 ,a nd m-(PDI) 2 :3 .1 cm À1 .H owever,u nfortunately these estimated values are unreliable because of underestimation of DE is due to the large contribution of the charge-transfer state.…”

Influence of Sulfur Oxidation State and Substituents on Sulfur-Bridged Luminescent Copper(I) Complexes Showing Thermally Activated Delayed Fluorescence

“…Our group has shown that varying the oxidation state at sulfur can have pronounced effects on the electronic properties of organic chromophores 42,43 and luminescent inorganic complexes. [44][45][46] In this study, the synthesis and optoelectronic characterization of a series of six new heteroleptic Cu(I) species utilizing sulfur-bridged dipyridyl ligands in either the sulfide 4 (II) or sulfone (VI) oxidation state as the N^N component, and bis [2-(diphenylphosphino)phenyl]ether (DPEPhos) as the P^P component are discussed.…”