Ultrafast Dynamics Of Typical ?,?-enones By Femtosecond Pump-probe Technology

Relaxation dynamics of molecules on excited states is of great importance to photophysics,photochemistry,biology,environment and other areas.Femtosecond laser and the pump-probe technology provide useful tools for researches on ultrafast relaxation dynamics of excites states molecules.By using femtosecond time-resolved photoelectron imaging and femtosecond time-resolved time of flight spectroscopy,the ultrafast relaxation progress can be traced in real time.?,?-enones are common functional groups in many biomolecules and drug molecules.The study of their non-radiative relaxation mechanism is the basis for understanding the photophysical and photochemical processes of biomolecules and drug molecules containing such functional groups.In this work,we adapt femtosecond time-resolved photoelectron images and femtosecond time-resolved time of flight spectroscopy to investigate the non-radiative relaxation mechanism and excited states properties of acrolein and crotonaldehyde,both of which are typical?,?-enones.The main contains of this study are summarized as following:1.Relaxation channels of S₁ state acrolein are studied by adopting 310-371 nm and 267 nm lasers as pump and probe light respectively.Experimental results show that acrolein molecules experience different relaxation channels with the change of excitation energy.The key factor that influences the relaxation pathways and the relative contributions of different components is the position of S₁/S₀ conical intersection.It is found that when the pumping energy is above the S₁/S₀ conical intersection,internal conversion(IC)can efficiently take place,while ISC cannot compete efficiently with IC.Furthermore,ISC can occur easily if molecules were pumped to lower energy zone below S₁/S₀ conical intersection but has lower transition probabilities as the excitation energy became lower following the Energy Gap Law.2.Real-time evolution of S₁ state crotonaldehyde is tracked by utilizing 310 nm and 365 nm lasers as pump pulses and 800 nm lasers as probe pulses respectively.Our experimental results show that crotonaldehyde molecule has experienced a quick internal conversion to the ground state in an ultrafast timescale of<100 fs following excitation to S₁ state both with 310 nm and 365 nm pumping.In addition,the energy of3s and different 3p Rydberg states of crotonaldehyde were assigned to be 3s=6.98±0.11 eV,3p_y=7.30±0.08 eV,3p_x=7.63±0.04 eV,and 3p_z=7.79±0.03 eV by combining the multi-peak time-resolved photoelectron spectroscopy and quantum chemistry calculation results.