Abstract
As new candidates of thiophene/phenylene co-oligomer (TPCO) species, 5,5′′-bis(4′-methoxy-[1,1′-biphenyl]-4-yl)-2,2′:5′,2′′-terthiophene (BP3T-OMe) and 4′,4′′′-([2,2′:5′,2′′-terthiophene]-5,5′′-diyl)bis(([1,1′-biphenyl]-4-carbonitrile)) (BP3T-CN) were synthesized for lasing applications. Although most unsubstituted TPCO species crystallize in monoclinic form, BP3T-OMe and BP3T-CN crystallized in orthorhombic and triclinic forms, respectively. Since the unsubstituted species, 5,5′′-bis(4-biphenylyl)-2,2′:5′,2′′-terthiophene (BP3T), shows unique and superior lasing performance in single crystals, the newly synthesized BP3T-OMe and BP3T-CN have possibilities to show different or improved optoelectronic characteristics. Amplified spontaneous emission (ASE) and optically pumped lasing were observed from both of the single crystals based on their well-shaped crystalline cavity and high group refractive index values of 3.7–5.3 for excellent light confinement. The lasing threshold for the BP3T-OMe crystal was lower than that for the BP3T-CN crystal, which was attributed to their different molecular orientation, standing in the former and inclining in the latter.
Highlights
Since the realization of an organic electroluminescence (EL) device composed of an anthracene single crystal reported by M
Electrically pumped gainnarrowed emissions have been recently reported from both organic light emitting diode (OLED) devices[15] and organic light emitting eld-effect transistor (OLEFET) devices.[16]
XRD measurements revealed crystal structures for both single crystals of BP3T-OMe (CCDC-1991924) and BP3T-CN (CCDC-1991925).† BP3T-OMe crystallized in an orthorhombic form (a 1⁄4 65.19 A, b 1⁄4 7.43 A, c 1⁄4 5.80 A, space group: Cmc[21], Z value: 4, cell volume: 2808 A3)
Summary
Since the realization of an organic electroluminescence (EL) device composed of an anthracene single crystal reported by M. The BP3T single crystal showed pulse-shaped light emission with several tens picoseconds delay relative to the excitation pulse at room temperature.[24,25] This time-delayed emission in contrast to the SE strongly suggests a cooperative light ampli cation process similar to super uorescence or polariton lasing.[25] As an origin of the delay time, phase relaxation to form a macroscopic ensemble of correlated emitters was expected among highly oriented molecules. Since the p–p* transition dipole moments are oriented parallel to the molecular long axis, the emitted light propagates in a transverse magnetic (TM) mode, and the light emission is con ned strongly inside a platelet single crystal. This condition of light con nement seems favourable for the formation of aforementioned macroscopic ensemble.
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