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)

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Summary

Introduction

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.

Results and discussion
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