ИСТИНА

Single crystals of thiophene-phenylene co-oligomers (TPCO) have demonstrated high potential for organic optoelectronics as they combine high charge carriers mobility and bright luminescence , . Various remarkable luminescence properties such as the spectrally-narrowed emissions3, self-wave-guide effect4, lasing4, and anisotropy of emission3 have been observed for the different TPCO crystal structures. Photoluminescence (PL) anisotropy reveals the average angular displacement between the absorption dipole moment and the emission one exposing the details of the electronic transitions within the crystalline structure. Thus, PL anisotropy studies can provide additional insights into high luminescence yield in TPCO crystals that has not been fully understood yet. In this contribution, we analyze anisotropy and kinetics of PL in single crystals of a novel TPCO (Fig.1a, top) 1,4-bis{5-[4-(trimethylsilyl)phenyl]thiophen-2-yl}benzene (AC5-TMS). Crystals were grown from solution and from the vapor phase. X-ray data show that the molecules are nearly flat-lying in the plane of the crystal plate (Fig.1a, bottom). PL spectra of the crystal are clearly different for X- and Y-polarized excitation (parallel and orthogonal to molecules backbones; Fig.1b), with the 450-nm band absent for the Y-polarized excitation. Surprisingly, the highest PL was observed for excitation polarization nearly orthogonal to the AC5-TMS backbone. However, PL is mainly polarized along the backbone regardless of the excitation polarization (Fig.1c). With the increase of the excitation wavelength from 400 to 445 nm, each PL spectral band decays noticeably slower (Fig. 1d). We will discuss the experimental data in the framework of the Davydov splitting model for AC5-TMS crystal packing.