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Highly-emissive mechanofluorochromic (MFC) organic solids changing their emission colors upon exposure to mechanical stimuli are highly demanded for various practical applications. In this work we introduced a planarizable by intramolecular N⋯H bond 2-((9H-fluoren-9-ylidene)methyl)pyridine fragment featuring an Aggregation-Induced Emission Enhancement and, particularly, MFC property for its bithiophene derivative. A two compounds, 2-((9H-fluoren-9-ylidene)methyl)-5-(5-phenylthiophen-2-yl)pyridine (FTP) and 2-((9H-fluoren-9-ylidene)methyl)-5-([2,2′-bithiophen]-5-yl)pyridine (FTT) were synthesized and fully characterized. In liquid solution both compounds are low emissive, however in the solid state they exhibit the photoluminescence quantum yield of 33% and 13% for FTP and FTT, respectively. Remarkably, the powder of FTT demonstrates a self-reversible mechanofluorochromism: the emission spectrum red-shifts after the grinding or pressurization and it recovers during one-day of storage without any treatment. The powder X-ray diffraction and differential scanning calorimetry revealed the reversible phase transition under temperature and mechanic stimuli. Analysis of molecular structure shows that in the gas phase FTT has a planar geometry while in the solid state it loses the flatness due to the crystal environment. Our results speak in favor of the increase of FTT planarity under the pressure to be responsible for the observed mechanofluorochromism. Image 1 • We introduce 2-((9H-fluoren-9-ylidene)methyl)pyridine (F) moiety for proper design of new materials. • Thiophenyl-phenylenе FTP derivative exhibits Aggregation-Induced Emission. • Bi-thiophenyl derivative (FTT) demonstrates a self-reversible mechanofluorochromism. • Pressure-induced planarization of FTT molecule in crystal is the origin of mechanofluorochromism. [ABSTRACT FROM AUTHOR]

Heteroaryl-containing co-oligomers are considered among the most promising materials for organic optoelectronics. In this work we synthesized a series of linear furan/phenylene co-oligomers (FPs) with different molecular length and studied their structure, luminescence and charge transport properties. The X-ray diffraction experiments revealed the higher distortion of molecular planarity for the longer FPs which is assigned to the crystal environment effect. All FPs demonstrated stability and high photoluminescence quantum yield (PL QY) both in solution and vapor-grown single crystals. The absolute PL QY as high as 70% was demonstrated for FP6 single crystal. The top-contact top-gate organic field-effect transistors (OFETs) demonstrated virtually the same mobility ∼0.35 cm 2 /Vs for a FPs with different conjugation chain. However the threshold voltage for the studied OFETs was demonstrated to be significantly reduced for a co-oligomer FP7 with longer conjugation chain. Thus we conclude that the increase of conjugation chain for co-oligomers does not benefit an increase of charge carrier mobility but improve the crystal/dielectric interface. [ABSTRACT FROM AUTHOR]