Quinoid‐Aromatic Resonance for Very Small Optical Energy Gaps in Small‐Molecule Organic Semiconductors: A Naphthodithiophenedione‐oligothiophene Triad System

Abstract

Organic semiconductors with very small optical energy gaps have attracted a lot of attention for nearinfrared-active optoelectronic applications. Herein, we present a series of donor-acceptor-donor (DÀ AÀ D) organic semiconductors consisting of a highly electron-deficient naphtho [1,2-b:5,6-b']dithiophene-2,7-dione quinoidal acceptor and oligothiophene donors that show very small optical energy gaps of down to 0.72 eV in the solid state. Investigation of the physicochemical properties of the DÀ AÀ D molecules as well as theoretical calculations of their electronic structures revealed an efficient intramolecular interaction between the quinoidal acceptor and the aromatic oligothiophene donors in the DÀ AÀ D molecules; this significantly enhances the backbone resonance and thus reduces the bond length alternation along the π-conjugated backbones. Despite the very small optical energy gaps, the DÀ AÀ D molecules have low-lying frontier orbital energy levels that give rise to airstable ambipolar carrier transport properties with hole and electron mobilities of up to 0.026 and 0.043 cm 2 V À 1 s À 1 , respectively, in field-effect transistors.

Quinoidal Acenedichalcogenophenediones for Near-Infrared-Absorbing Organic Semiconductors: Effects of Chalcogen Atom Substitution on the Physicochemical and Carrier Transport Properties

“…The synthesis of BXQnTs and NXQnTs was carried out according to our previously reported procedure (Scheme 1). 18 First, the trialkylsilyl-substituted thiophene or 2-butyloctyl-substituted bithiophene donor units were introduced at the β-positions of acenedichalcogenophenes to afford the precursor molecules (BXnTs or NXnTs) in 59−96% yields. Then, the α-positions of the central acenedichalcogenophene in the precursor molecules were lithiated with n-butyllithium, borylated with triisopropyl borate, and then hydrolyzed to afford the corresponding boronic acids, which were immediately treated with hydrogen peroxide to give the target BXQnTs and NXQnTs in 10−57%.…”

“…3,7-Dibromobenzo­[1,2- b :4,5- b ′]­difuran, 2,6-bis­(trimethylsilyl)-3,7-diiodobenzo­[1,2- b :4,5- b ′]­diselenophene, 2-(dimethyl- tert -butylsilyl)-5-(tributylstannyl)­thiophene, 2-(triisopropylsilyl)-5-(tributylstannyl)­thiophene, and (5′-(2-butyloctyl)-[2,2′-bithiophen]-5-yl)­trimethylstannane were synthesized according to the literature. NMR spectra were recorded on Bruker Avance III 500 NMR or JEOL JNM-ECS400 spectrometers.…”

“…Based on the systematic investigation of the structures and properties, of the isoelectronic series of BXQnTs and NXQnTs as well as theoretical calculations, we discuss here how the chalcogen atom substitution does or does not affect their semiconductor material properties, which is important for rational molecular design for superior NIR-organic semiconductors based on the acenedichalcogenophenediones. 38 2-(dimethyl-tert-butylsilyl)-5-(tributylstannyl)- thiophene, 39 2-(triisopropylsilyl)-5-(tributylstannyl)thiophene, 40 and (5′-(2-butyloctyl)-[2,2′-bithiophen]-5-yl)trimethylstannane 18 were synthesized according to the literature. NMR spectra were recorded on Bruker Avance III 500 NMR or JEOL JNM-ECS400 spectrometers.…”

“…Such a quinoid-aromatic resonance effect can also be expected for para -benzoquinoidal acceptors. For example, benzodipyrrolidone (Figure b) has been incorporated into D-A polymers, showing very small optical energy gaps as low as 0.79 eV. , In addition, we have reported that a series of para - quinoidal benzo- or naphtho-dithiophenediones are also promising acceptor units for NIR-absorbing organic semiconductors when incorporated in thiophene-based polymers and oligomer. , Particularly, naphthodithiophenedione-based D-A-D triads in the solid state exhibited optical energy gaps as low as 0.72 eV while keeping the low-lying E HOMO s and E LUMO s below −5.0 and −4.0 eV, respectively. The OFET devices based on the triads exhibited hole and electron mobilities on the order of 1 × 10 –2 cm 2 V –1 s –1 in air.…”