Third order nonlinear optical properties and transient dynamics of thiophene-contained pyrene derivatives: Effect of peripheral substituent group

In this work, two pyrene derivatives with delocalized π-electron system 1-(pyren-1-yl)−3-(5-Chlorothiophene-2-yl)acrylic ketone (1612) and 1-(pyren-1-yl)−3-(5-Phenylthiophene-2-yl) acrylic ketone (1613) were synthesized. The third-order nonlinear optical (NLO) response of these compounds dissolved in DMSO were investigated using Z-scan technique with 190 fs laser pulses at 532 nm. Large two-photon absorption was found for the two compounds, while the NLO response of 1613 was larger than 1612. The femtosecond transient absorption (TA) results demonstrate that both compounds have broad TA absorption band over the visible regime. Compared to 1612, the TA band of 1613 exhibit a 15-nm blue shift of its peak while its UV-Vis absorption peak have 50 nm red-shift. Meanwhile, the TA decay curve also show that the excited-state lifetime of 1613 is longer, indicating the substituent group functionalization also has a significant impact on the excited-state relaxation processes. Our results show that both the NLO response and photo-physical dynamics of pyrene chromophores are readily tunable via peripheral substituent group, which is essential for the development of novel NLO materials based on this conjugated molecules.