氢键效应对2,3-二氢-3-酮基-1H-吡啶并[3,2,1-kl]吩噻嗪光物理性质的影响

利用含时密度泛函理论(TDDFT)方法和飞秒时间分辨的瞬态吸收光谱技术对2,3-二氢-3-酮基-1H-吡啶并3,2,1-kl]吩噻嗪(PTZ4)和3-酮基-1H-吡啶并3,2,1-kl]吩噻嗪(PTZ5)这两种荧光探针分子的光物理性质进行了研究. TDDFT结果表明PTZ4和PTZ5在甲醇溶液形成了氢键络合物导致它们吸收峰的红移. PTZ4分子在基态有四种稳定构型，其在四氢呋喃溶液中的双荧光峰正是来自于四种构型下的内部电荷转移态. PTZ4分子在四氢呋喃和甲醇溶液中的瞬态吸收光谱表明，从局域态到转移态的弛豫时间常数在四氢呋喃中为16.0 ps，在甲醇中为7.5 ps；PTZ4分子在甲醇中的激发态寿命为53.8 ps，而这种超短的寿命可能是由于PTZ4分子在激发态时形成的面外型氢键络合物导致的.

Hydrogen Bonding Effects on the Photophysical Properties of 2,3-dihydro-3-keto-1H-pyrido[3,2,1-kl]phenothiazine

Time-dependent density functional theory (TDDFT) and femtosecond transient absorption spectroscopy were used to investigate the photophysical properties of 2,3-dihydro-3-keto-1H-pyrido3,2,1-kl]phenothiazine (PTZ4) and 3-keto-1H-pyrido3,2,1-kl]phenothiazine (PTZ5). The calculated results obtained from TDDFT suggest that the red-shifts of the absorption spectra of these two fluorophores in methanol are due to the formation of hydrogen-bonded complexes at the ground state. Four conformers of PTZ4 were obtained by TDDFT. The two fluorescence peaks of PTZ4 in tetrahydrofuran (THF) came from the ICT states of the four conformers. The fluorescence of PTZ4 in THF showed a dependence on the excitation wavelength because of butterfly bending. The excited state dynamics of PTZ4 in THF and methanol were obtained by transient absorption spectroscopy. The lifetime of the excited PTZ4 in methanol was 53.8 ps, and its relaxation from the LE state to the ICT state was completed within several picoseconds. The short lifetime of excited PTZ4 in methanol was due to the formation of out-of-plane model hydrogen bonds between PTZ4 and methanol at the excited state.