Helicenes with persistent phosphorescence (τ_p > 600 ms) and strong circular polarization phosphorescence (|g_lum| ∼ 0.015) were synthesized through the fusion of ortho-fused benzene rings and thieno[2,3-b:3′,2′-d]thiophene (DTT).

The construction of multiple helicenes, one of the important branches of curved polyaromatic hydrocarbons (PAHs), is a fundamental goal in both helicene chemistry and supramolecular chemistry. Here, we demonstrate the facile and efficient construction of four thiophene/selenophene-based windmill-shaped triple [6]helicenes. The key step involved was the oxidative photocyclization of four 1,3,5-tris(2-(5-(trimethylsilyl)dithieno/diseleno[2,3-b:3′,2′-d]thiophen/selenophen-2-yl)vinyl)benzenes in the presence of iodine in dry toluene. The windmill-shaped molecular structures of triple [6]helicenes were confirmed by X-ray crystallographic analysis. With the replacement of S with Se in molecular skeletons, the racemic triple [6]helicenes exhibited different crystal-packing patterns based on multiple intermolecular interactions. The novel capsule structures of the racemic triple [6]helicenes were formed by two enantiomers based on the intermolecular interactions. The chiral resolution of the third racemic triple [6]helicene was carried out via chiral HPLC, and the chiroptical properties such as the CD spectra and optical rotations of the enantiomers were investigated. Furthermore, the spectroscopic and physicochemical behaviors of the racemic triple [6]helicenes showed that the heteroatom replacement of S with Se could precisely modulate their emission properties and molecular energy levels.

External pressure can regulate photophysical property and charge transport performance of organic semiconductor, however, the underlying mechanism at the microscopic level is still elusive. Using thermal vibrational correlation function coupled quantum mechanism/molecular mechanism and full quantum charge transfer rate theory, we systematically explore the influence of pressure on fluorescence emission and charge transport behaviours of representative cyclooctatetrathiophene (COTh). It is found that, upon pressurization, the intramolecular configurations of COTh became more twisted, leading to the blue-shifted emission. The fluorescence quantum efficiency (FQE) of COTh crystals decreases monotonically in a wide pressure range of 0 - 4.38 GPa, because the simultaneously decrease of internal conversion rate constant (k_ic) and the increase of intermolecular energy transfer rate constant (k _eet), and the variation of k_eet is dominant. The decrease of k_ic is attributed by reorganization energy decreasing, reflecting the suppression of the low-frequency flipping vibrations of four thiophene rings and the high-frequency stretching vibrations of central cyclooctatetraene, while the keet increase is due to the simultaneously increase of exciton coupling and spectra overlap. Moreover, we predicted that the hole mobility of COTh increases monotonically by nearly an order of magnitude from 0.39 to 3.00 cm² V^-1 s^-1 upon compression, because of the increase of transfer integral and the decrease of charged reorganization energy. And its hole mobility exhibits obvious anisotropy. Our work systematically builds the external pressure, molecular packing and photoelectric properties relationships of organic semiconductors and provides a theoretical guidance for rational design of pressure responsive organic semiconductors with excellent photoelectric performance.