Study On The Photophysical Properties Of The Triplet State Of Perylene-containing Compounds

The long-lived triplet excited state is beneficial to the applications of the triplet photosensitizers in energy transfer and electron transfer.Therefore,it is crucial to explore the methods for designing of triplet photosensitizers to obtain the long-lived triplet state.Charge recombination(CR)induced intersystem crossing(ISC)in compact orthogonal electron donor-acceptor dyads,which termed spin-orbit charge transfer intersystem crossing(SOCT-ISC),can be a novel strategy to design heavy atom-free triplet photosensitizers,because the synthesis of such compact electron donor-acceptor dyads without heavy atom is feasible,and the molecular structure can be feasibly modified to optimize the photophysical properties.However,the current research on the systems based on the SOCT-ISC mechanism is not sufficient,and it is necessary to develop more molecular structures and explore the relationship between the molecular structures and SOCT-ISC efficiency.In this thesis,perylene was selected as the chromophore and electron acceptor for designing compact electron donor-acceptor dyads showing the SOCT-ISC mechanism,and the effect of molecular configuration on SOCT-ISC efficiency and the photophysical properties of the compounds were studied.Steady state/transient spectroscopy and theoretical calculations were used to investigate the influence of different substitution positions on the photophysical properties of perylene derivatives.The electron donor rhodamine(Rho,lactam form)moiety is attached via the N-C bond to the electron acceptor at either 1-or 3-position of the perylene(Pery)moiety(Rho-Pery-1 and Rho-Pery-3).Severe torsion of the Pery moiety in Rho-Pery-1 was observed.The fluorescence of the two dyads is significantly quenched in polar solvents,and the singlet oxygen quantum yields(Φ_Δ)are strongly dependent on solvent polarity(4-36%).Femtosecond transient absorption spectra demonstrate that charge separation(CS)is fast(0.51-5.75 ps),and the charge recombination(CR)-induced ISC is slow(>3 ns).Nanosecond transient absorption spectra indicate that the formation of triplet states via SOCT-ISC takes 24-75 ns for Rho-Pery-1 and 6-15 ns for Rho-Pery-3,and the distorted π-framework of the Pery moiety results in a shorter triplet lifetime of 19.9 μs.Time-resolved electron paramagnetic resonance(TREPR)spectroscopy confirms the SOCT-ISC mechanism.The study of nitroperylene derivatives found that the UV-vis absorption spectra are very different when the substitution position is changed.The fluorescence spectra were found strongly depends on solvent polarity,denoting a substantial charge-transfer character of the S1 state.The singlet oxygen quantum yield of 3-NO2-Pery is 33%in non-polar solvent(n-hexane),and Φ_Δ are negligible in polar solvents,the main inactivation way of the S1 state is internal conversion.Theoretical calculations show that N atom of aminoperylene is involved in the π-conjugation system,and the first electronic transition is with CT character.Important solvent dependences of the steady state spectra as well as the transient absorption spectra are observed in aminoperylene.