Impact of material parameters on strong exciton-photon coupling states formed in microcrystal resonators of p- and n-type thiophene/phenylene co-oligomers

Microcrystals with different orientations of thiophene/phenylene co-oligomers (TPCOs) serving as Fabry-Perot microresonators were prepared using a miniemulsion technique with modification. Reflecting molecular packings and crystal structures, p-type 5,5 '-bis(4-biphenylyl)-2,2 '-bithiophene (BP2T) and n-type 5,5 '-bis(4 '-cyanobiphenyl-4-yl)-2,2 '-bithiophene (BP2T-CN) grow in square-shaped (microplatelet) and rod-shaped (microrod) microcrystals, respectively. Strong exciton-photon coupling was demonstrated for BP2T (Rabi splitting energy omega: 1.05 eV) and BP2T-CN (omega: 1.25 eV) microcrystals owing to their active microresonators providing effective photonic mode confinement. We find that the strength of the coupling between excitons and photons is correlated with the refractive index and absorption coefficient originating from the transition dipole moment and oscillator strength. For BP2T-CN, a larger value of omega was achieved because of a higher absorption coefficient, larger refractive index, and smaller mode volume.

Automated summary

Microcrystals with different orientations of thiophene/phenylene co-oligomers (TPCOs) were prepared as Fabry-Perot microresonators using a miniemulsion technique. Strong exciton-photon coupling was demonstrated for BP2T and BP2T-CN microcrystals owing to their active microresonators providing effective photonic mode confinement. The strength of the coupling between excitons and photons is correlated with the refractive index and absorption coefficient originating from the transition dipole moment and oscillator strength, with BP2T-CN achieving a larger value of omega due to its higher absorption coefficient, larger refractive index, and smaller mode volume.