Photoinduced Charge Separation Prompted Intervalence Charge Transfer in a Bis(thienyl)diketopyrrolopyrrole Bridged Donor‐TCBD Push‐Pull System

Abstract

Intervalence charge transfer (IVCT), aphenomenon observed in molecular systems comprised of two redox centers differing in oxidation states by one unit, is reported in anovel, newly synthesized, multi-modular donor-acceptor system comprised of central bis(thienyl)diketopyrrolopyrrole (TDPP) hosting two phenothiazine-tetracyanobutadiene (PTZ-TCBD) entities on the opposite sides.One-electron reduction of TCBD promoted electron exchange between the two TCBD resulting in IVCT transition in the near-infrared region. The stabilization energy, ÀDG com and comproportionation equilibrium constant, K com calculated from peak potentials of the split reduction waves were found to be 1.06 10 4 Jmol À1 ,a nd 72.3 M À1 ,r espectively.F urther,t he IVCT transition was also witnessed during the process of thermodynamically feasible electron transfer upon excitation of the TDPP entity in the system, and served as ad iagnostic marker to characterizet he electron transfer product. Subsequent transient absorption spectral studies and data analysis by Global and Target analyses revealed occurrence of ultrafast charge separation (k cs % 10 10 s À1 )owing to the close proximity and good communication between the entities of the multi-modular donoracceptor system. The role of central TDPP in promoting IVCT is borne out from the present investigation.

Using diketopyrrolopyrroles to stabilize double excitation and control internal conversion

“…Two possible effects might play a role in stabilizing the dark state: i) the increase of 𝜋 scaffold, ii) the donor-acceptor effect of the DPP and thiophene moieties or both. 15,16 To assess which one dominates, we systematically increased the number of π-electrons in the scaffold around T=T by adding up to four (-CH=CH-)n units (Figure 1g-j). Those derivatives are referred to as ETn, where n is the number of (-CH=CH-) units.…”

“…They strongly absorb visible light, show significant electron-withdrawing effects, and possess high electron mobility. [8][9][10][11][12] Due to these properties, DPPs are often used as an electron-acceptor unit to design optoelectronic devices 13,14 such as new push-pull polymers, 15,16 organic light-emitting diodes, 17 and more recently, singletfission chromophores. 8,18,19 Motivated by the design of new intramolecular singlet-fission materials, Mukhopadhyay et al 20 proposed a combination of a thiophene-DPP derivative (with charge-transfer (CT) character) with a vinyl linker (polyene character) (Figure 1b).…”

Using diketopyrrolopyrroles to stabilize double excitation and control internal conversion

“…They strongly absorb visible light, show significant electron-withdrawing effects, and possess high electron mobility. 8–12 Due to these properties, DPPs are often used as an electron-acceptor unit to design optoelectronic devices 13,14 such as new push–pull polymers, 15,16 organic light-emitting diodes, 17 and more recently, singlet-fission chromophores. 8,18,19…”

“…They strongly absorb visible light, show significant electron-withdrawing effects, and possess high electron mobility. [8][9][10][11][12] Due to these properties, DPPs are often used as an electron-acceptor unit to design optoelectronic devices 13,14 such as new push-pull polymers, 15,16 organic light-emitting diodes, 17 and more recently, singlet-fission chromophores. 8,18,19 Motivated by the design of new intramolecular singletfission materials, Mukhopadhyay et al 20 proposed a combination of a thiophene-DPP derivative (with charge-transfer (CT) character) with a vinyl linker (polyene character) (Fig.…”

Phenothiazine and phenothiazine-5,5-dioxide-based push–pull derivatives: synthesis, photophysical, electrochemical and computational studies

“…31,32 The electron-rich alkynes react with cyanobased strong electron acceptor tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) via [2+2] cycloaddition retroelectrocyclic ring-opening reaction, which results in donor-acceptor-based p-conjugated molecular systems in excellent yield. [33][34][35][36] Diederich, Michinobu, Shoji, Butenscho ¨n, Kato, and Trolez et al have explored the TCBD and cyclohexa-2,5diene-1,4-diylidene-expanded TCBD substituted derivatives as redox-active ICT chromophores for various optoelectronic applications. 34,[37][38][39][40][41][42][43][44][45] Recently, our group has reported a series of push-pull TCBD and cyclohexa-2,5-diene-1,4-diylidene-expanded TCBD functionalized phenothiazine dimers.…”