Synthesis of B←N embedded indacenodithiophene chromophores and effects of bromine atoms on photophysical properties and energy levels. Issue 32 (9th August 2018)

• Record Type: Journal Article
• Authors: Li, Yongchun; Meng, Huifeng; Yan, Dong; Li, Yuqing; Pang, Bo; Zhang, Kai; Luo, Genggeng; Huang, Jianhua; Zhan, Chuanlang
• Is Part Of: Tetrahedron. Volume 74:Issue 32(2018)
• Page Start: 4308
• Page End: 4314
• Publication Date: 2018-08-09
• Subjects: B←N coordination -- Indacenodithiophene -- Structural modification -- Photophysical properties -- Energy levels; Chemistry, Organic -- Periodicals; 547.005
• DOI: 10.1016/j.tet.2018.06.035
• Languages: English
• ISSNs: 0040-4020

Abstract

Abstract: Developing novel fused π-conjugated chromophores has been an energetic research realm and knowing how to adjust their photophysical properties and energy levels through structure tailoring is of pivotal importance. Herein, based on the ladder-type π-conjugated indacenodithiophene (IDT) moiety, four B←N embedded IDT structures, namely, BNIDT, BNIDT-2Br, BNIDT-4Br, andBNIDT-6Br are synthesized and fully characterized. The influences of B←N unit embedded in the IDT backbone and Br atoms anchoring at the periphery on the photophysical properties and energy levels are discussed systematically. From IDT toBNIDT, a new intra-molecular charge transfer (ICT) transition band appears at lower energy (400–600 nm) in the absorption spectra with reduced optical bandgaps ( E g ) from 3.25 eV to 2.11 eV and the fluorescence emission peaks red-shift from 390 nm to 565 nm along with remarkably extended fluorescence lifetimes from 1.2 ns to 12.4 ns due to the introduction of electron-deficient B←N into the backbone. Further anchoring Br atoms at the periphery of the backbone gives rise to depressed optical bandgaps, decreased fluorescence quantum yields (Φ), and shortened fluorescence lifetimes (τ) fromBNIDT ( E g = 2.11 eV, Φ = 0.46, τ = 12.4 ns), BNIDT-2Br ( E g = 2.08 eV, Φ = 0.18, τ = 4.9 ns), BNIDT-4Br ( E g = 1.67 eV, non-emission) toBNIDT-6Br ( E g = 1.61 eV, non-emission). The HOMO and LUMO levels estimated from ultraviolet photoelectron spectroscopy (UPS) and optical bandgaps also experience synergetic lowering from IDT toBNIDT-6Br . This work indicates that backbone modification with electron-deficient B←N unit and side groups tailoring with halogen atoms are powerful to manipulate the optical properties and energy levels of fused π-conjugated chromophores. Graphical abstract: