Resonant stimulation of Raman scattering from single-crystal thiophene/phenylene co-oligomers

Abstract

Amplified Raman scattering was observed from single crystals of thiophene/phenylene co-oligomers (TPCOs). Under ns-pulsed excitation, the TPCO crystals exhibited amplified spontaneous emission (ASE) at resonant absorption wavelengths. With increasing excitation wavelength to the 0-0 absorption edge, the stimulated resonant Raman peaks appeared both in the 0-1 and 0-2 ASE band regions. When the excitation wavelength coincided with the 0-1 ASE band energy, the Raman peaks selectively appeared in the 0-2 ASE band. Such unusual enhancement of the 0-2 Raman scattering was ascribed to resonant stimulation via vibronic coupling with electronic transitions in the uniaxially oriented TPCO molecules.

Cooperative Behaviors in Amplified Emission from Single Microcrystals of Thiophene/Phenylene Co‐Oligomers toward Organic Polariton Laser

“…However, the Raman intensity is selectively enhanced when the λ ex is fixed in a specific off‐resonant energy. Since this behavior is inconsistent with the usual SRRS process, we examined the λ ex ‐dependences and polarization effects of Raman characteristics in detail …”

“…c) Raman peak intensity in the 0–2 band as a function of λ ex (closed square), ASE spectrum in the 0–1 band (dashed line), and PLE spectrum at λ em = 623 nm (red line) taken from single‐crystal BP3T at 12 K. d) Schematic diagram for the enhanced Raman scattering in the 0–2 band under off‐resonant excitation corresponding to the 0–1 transition energy. Reproduced with permission . Copyright 2013, AIP Publishing.…”

“…With increasing λ ex , λ em of these peaks accordingly shift to the longer wavelength. Since the energy differences between λ ex and λ em of the two peaks are kept constant at 1450 and 1600 cm −1 , these peaks correspond to Raman scattering based on the molecular vibrations with the A 1 and B 1 stretching modes of the C 2v ‐symmetric BP1T molecule, respectively …”

Synthesis and characterization of methoxy- or cyano-substituted thiophene/phenylene co-oligomers for lasing application

“…However, BP3T single crystals show unusual light amplication behaviour, which cannot be explained by the conventional stimulated emission (SE) process. Stimulated resonant Raman scattering (SRRS) was observed from a BP3T single crystal at 12 K, 22 which indicates an existence of coherent molecular vibrations. The SRRS has also been observed for other TPCO single crystals even at room temperature with emission lines more narrow than that of ASE even without any cavity structure, 22,23 and their light emission wavelength can be tuned by changing the excitation wavelength.…”

Optically Pumped Lasing Based on Vibrationally Dressed Exciton Polaritons in a Single-Crystal Molecular Cavity at Room Temperature

“…18,24,25 (iv) Mirrorless lasing based on stimulated resonance Raman scattering (SRRS) has been observed in BP3T and other TPCO single crystals, suggesting a formation of coherent molecular vibrations. 26,27 Although those unusual light amplification behaviors have been phenomenologically well-investigated for TPCO single crystals, their detailed descriptions have not been well established. Exciton polaritons (EPs) are one of the reliable candidates for those cooperative light emissions as reported for inorganic and organic semiconductor microcavities.…”