Enhancing excited-state population of perylenequinone photosensitizer with asymmetric laser pulses

Perylenequinones are important photosensitizers commonly used in photodynamic therapy (PDT) due to their efficient photoreactivity and photostability, which originate from excited state intramolecular proton transfer (ESIPT). Herein, the mechanisms of ESIPT are explored through first-principle calculations, and the slowly-turned-on and rapidly-turned-off (STRT) laser pulse steered ground and excited states population redistribution of perylenequinone is characterized by employing time-dependent wave packet methods. It is revealed that the strengthened hydrogen bond favors proton transfer in the S1 state, and due to enhanced non-resonant excitation and reduced energy exchange between the wave packet and external field during the falling period, the asymmetric pulses could increase the excited-state population, leading to improved excitation efficiency. Compared to traditional Gauss-type laser pulses, the optimization of STRT parameters (i.e., falling time, intensity, and wavelength) could bring more population in the excited state (>80%) and promote subsequent proton transfer processes that are responsible for enhancing therapeutic effects during PDT. The present work offers valuable insights into the interactions between external fields and molecules, paving the way for optimized drug delivery systems with minimal damage to normal tissue and enhanced therapeutic efficacy.