Chantler Paul Alexander, Thomsen Lars, Roychoudhury Subhayan, Glover Chris J, Mitchell Valerie, McGregor Sarah K M, Lo Shih-Chun, Namdas Ebinazar B, Prendergast David, McNeill Christopher R
Department of Materials Science and Engineering, Monash University, Wellington Road, Clayton, Victoria 3800, Australia.
Australian Synchrotron, ANSTO, 800 Blackburn Road, Clayton, Victoria 3168, Australia.
J Chem Phys. 2024 Nov 14;161(18). doi: 10.1063/5.0231117.
Alkylated benzothienobenzothiophenes are an important class of organic semiconductors that exhibit high performance in solution-processed organic field-effect transistors. In this work, we study the near-edge x-ray absorption fine-structure (NEXAFS) spectra of 2,7-didecyl[1]benzothieno[3,2-b][1]benzothiophene (C10-BTBT) at both the carbon and sulfur K-edges. Angle-resolved experiments of thin films are performed to characterize the dichroism associated with molecular orientation. First-principles calculations using the density functional theory-based many-body x-ray absorption spectroscopy (MBXAS) method are also performed to correlate the peaks observed and their dichroism with transitions to specific antibonding molecular orbitals. Interestingly, the dichroism of the dominant, lowest energy peak is opposite at the carbon and sulfur K-edges. While the low-energy peak at the carbon K-edge is assigned to carbon 1s → π* transitions with transition dipole moment (TDM) perpendicular to the planar BTBT core, the dominant low energy peak at the sulfur K-edge is assigned to sulfur 1s → σ* transitions with TDM oriented along the long axis of the BTBT core. These differences at the sulfur and carbon K-edges are understood through the MBAXS simulations that find a reordering of the energy of the lowest energy π* and σ* transitions at the sulfur K-edge due to the strong localization of the σ* orbital over the sulfur atom. This work highlights differences in the NEXAFS spectra of organic semiconductors at carbon and sulfur K-edges and provides new insights into peak assignment and x-ray dichroism relevant for studying the molecular orientation of organic semiconductor films.
烷基化苯并噻吩并苯是一类重要的有机半导体，在溶液处理的有机场效应晶体管中表现出高性能。在这项工作中，我们研究了2,7-二癸基[1]苯并噻吩并[3,2-b][1]苯并噻吩（C10-BTBT）在碳和硫K边的近边X射线吸收精细结构（NEXAFS）光谱。对薄膜进行了角分辨实验，以表征与分子取向相关的二色性。还使用基于密度泛函理论的多体X射线吸收光谱（MBXAS）方法进行了第一性原理计算，以将观察到的峰及其二色性与向特定反键分子轨道的跃迁相关联。有趣的是，在碳和硫K边，占主导地位的最低能量峰的二色性是相反的。虽然碳K边的低能峰被指定为碳1s→π跃迁，其跃迁偶极矩（TDM）垂直于平面BTBT核，但硫K边的主导低能峰被指定为硫1s→σ跃迁，其TDM沿BTBT核的长轴取向。通过MBXAS模拟可以理解硫和碳K边的这些差异，该模拟发现由于σ轨道在硫原子上的强定位，硫K边最低能量π和σ*跃迁的能量发生了重新排序。这项工作突出了有机半导体在碳和硫K边的NEXAFS光谱差异，并为研究有机半导体薄膜分子取向相关的峰归属和X射线二色性提供了新的见解。
