Presentation Information
[23p-1BC-12]Excited-State Dynamics Study with Thiophene/Phenylene Co-Oligomer Nanocrystals
〇(D)Andi Marwanti Panre1, Hitoshi Mizuno1, Tomomi Jinjyo1, Hiroyuki Katsuki1 (1.NAIST)
Keywords:
Excited-state dynamics,Organic nanocrystals,Optical properties
Although size effects in organic nanocrystals (NCs) have been reported for perylene and anthracene NCs, there are very few studies on the size effect mechanism and excited-state dynamics in organic NCs.[1-3] Jinjyo, et al. have recently reported[4] the size-dependent photoluminescence (PL) and absorption properties of thiophene/phenylene co-oligomer (TPCO) NCs. In the present study, we performed transient absorption spectroscopy with 5,5’-bis(4’-cyanobiphenyl-4-yl)-2,2’-bithiophene (BP2T-CN) NCs which is a kind of TPCOs in addition to the measurements of morphology, crystallinity, and fundamental optical properties. BP2T-CN NCs with average sizes of 86 nm and 103 nm were prepared by the reprecipitation method and showed green and yellow emissions, respectively. The PL spectra of these NCs are shown in Fig.1a. At the NCs with a size of 86 nm, the peak energy of the PL spectrum was blue-shifted by 0.27 eV and PL lifetime of the 0-1 band is decreased, as shown in Fig. 1b. As in the case of BP2T NCs, this is due to the surface and quantum effects (number of constituent molecules dependent site-shift effect, exciton confinement).[4] Moreover, photoinduced absorption bands (ΔT/T < 0) in the yellow-emitting BP2T-CN NCs appeared at 490 nm and 680 nm, as shown in Fig 1c. The transient absorption signal at 680 nm is characterized by three exponential decays with 0.65 ps, 2.3 ps, and 75 ps components, as shown in Fig. 1d. These time constants shed light on relaxation processes, including electron trapping, intra-band relaxation, and non-radiative decay.