Comprehensive investigation of the ultrafast excited state dynamics and nonlinear optical properties of pyrene derivatives with different push-pull properties.

The intramolecular charge transfer (ICT) process is an essential phenomenon in nonlinear optical (NLO) materials. Tuning the ICT process in a molecule can be used to modify its linear or NLO properties. Over the years, ICT processes have been explored in organic molecules exhibiting "push-pull" characteristics, where donor-acceptor moieties are connected directly or a π bridge. In this study, we synthesized three D-π-A pyrene derivatives, namely TA-4, TA-7, and TA-8, with varying push-pull characteristics to examine the effect of ICT on excited state absorption (ESA) and NLO properties using fs transient absorption spectroscopy (TAS) and -scan experiments, respectively. TAS showed the superposition of locally excited (LE) state based ESA and ICT-based ESA, effectively broadening the ESA at a longer time delay influencing their NLO properties. All three derivatives demonstrated a higher degree of ICT, and their relaxation dynamics were influenced by solvent polarity. The Z scan study indicates an enhancement in two-photon absorption value, and a variation in non-linear refractive index () at higher laser intensity, showing their potential for applications in nonlinear optical devices.