Ultrafast Charge Transfer Dynamics of Near-Infrared Emitting Nitro-Terrylenediimides

Investigation of photoinduced exciton dynamics of nitrated rylenediimides can pave the way for a comprehensive understanding of their unique deactivation pathways and utility in future optoelectronic devices. Herein, we present the detailed excited state dynamics of a series of near-infrared (NIR) emitting nitrated terrylenediimide derivatives (TDI-m-NO2, TDI-d-NO2, and TDI-t-NO2). The incorporation of strong electron-withdrawing nitro groups in the bay position of the terrylene core resulted in the intramolecular charge transfer character (CT) revealed from the steady-state measurements. The transient absorption measurements of nitro-terrylenediimides in the femtosecond time domain enabled the investigation of the spectral evolution and kinetics of the CT state upon photoexcitation. Further, the solvent-assisted relaxation dynamics of the CT state were explored in toluene (TOL), tetrahydrofuran (THF), and acetonitrile (ACN), which revealed the faster decay time of the CT state to the ground state with increasing solvent polarity (TDI-m-NO2, τCT→GS(TOL) = 0.68 ns and τCT″→GS(ACN) = 0.20 ns; TDI-d-NO2, τCT→GS(TOL) = 1.42 ns and τCT″→GS(ACN) = 0.21 ns; and TDI-t-NO2, τCT→GS(TOL) = 0.46 ns and τCT″→GS(ACN) = 0.18 ns). The work presents an in-depth analysis of the photoexcited state dynamics of a series of extended π-conjugated nitroaromatic chromophores exhibiting emission in the NIR range.