Synthesis, optical and electrochemical properties of 4,4′-bibenzo[c]thiophene derivatives

We designed and synthesized unsubstituted 4,4 '-bibenzo[c]thiophene 4,4 '-BBT and its silyl-substituted derivatives 1,1 '-Si-4,4 '-BBT and 1,1 ',3,3 '-Si-4,4 '-BBT with one or two tert-butyldimethylsilyl groups on each thiophene ring, as new pi-building blocks in emitters, photosensitizers and semiconductors for organic optoelectronic devices. The characterization of 4,4 '-BBT, 1,1 '-Si-4,4 '-BBT and 1,1 ',3,3 '-Si-4,4 '-BBT was successfully determined by FTIR, H-1 and C-13 NMR measurements, high-resolution mass spectrometry (HRMS) analysis, photoabsorption and fluorescence spectroscopy, cyclic voltammetry (CV) and density functional theory (DFT) calculations. Moreover, a single-crystal X-ray structural analysis was successfully made for 1,1 '-Si-4,4 '-BBT and 1,1 ',3,3 '-Si-4,4 '-BBT. The photoabsorption and fluorescence maxima (lambda absmax and lambda flmax) of the three 4,4 '-bibenzo[c]thiophene derivatives in toluene exhibit bathochromic shifts in the order of 4,4 '-BBT (359 nm and 410 nm) < 1,1 '-Si-4,4 '-BBT (366 nm and 420 nm) < 1,1 ',3,3 '-Si-4,4 '-BBT (371 nm and 451 nm). The HOMO and LUMO energy levels rise in the order of 4,4 '-BBT (-5.55 eV and -2.39 eV) < 1,1 '-Si-4,4 '-BBT (-5.45 eV and -2.34 eV) < 1,1 ',3,3 '-Si-4,4 '-BBT (-5.34 eV and -2.30 eV), but the rise of the HOMO energy level is larger than that of the LUMO energy level, resulting in the bathochromic shift of the photoabsorption band from 4,4 '-BBT to 1,1 ',3,3 '-Si-4,4 '-BBT. The fluorescence quantum yields (phi(fl)) of 4,4 '-BBT, 1,1 '-Si-4,4 '-BBT and 1,1 ',3,3 '-Si-4,4 '-BBT in toluene are 0.41, 0.41 and 0.36, respectively. It is worth mentioning that in the solid state 1,1 '-Si-4,4 '-BBT and 1,1 ',3,3 '-Si-4,4 '-BBT show relatively high phi(fl-solid) values of 0.22 and 0.25, respectively, whereas 4,4 '-BBT exhibits poor solid-state fluorescence properties (phi(fl-solid) < 0.02). This work provides an efficient synthetic method for the 4,4 '-bibenzo[c]thiophene derivatives and their photophysical properties in the solution and solid state, electrochemical properties and X-ray crystal structures.

Automated summary

The study focused on the design and synthesis of three 4,4'-bibenzo[c]thiophene derivatives, with subsequent characterization using various analytical techniques. Variations in photophysical properties and energy levels were observed in both solution and solid state environments for the derivatives.