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

Abstract

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-pyrido[3,2,1-kl]phenothiazine (PTZ4) and 3-keto-1H-pyrido[3,2,1-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.

Effects of Solvent Dielectric Constant and Viscosity on Two Rotational Relaxation Paths of Excited 9-(Dicyanovinyl) Julolidine

“…Recently, a detailed potential energy surface of the excited state of DCVJ was frequently reported. ,,,, It was reported that there are two kinds of twist decay paths, τ b and τ c , for excited DCVJ. , The disadvantageous application of the previous reported modes to DCVJ may be induced by the two different rotational decay paths in DCVJ. The solvents have shown important effects on the excited-state dynamics of fluorophores, − but seldom people reported the solvent effects on the rotational decays of DCVJ. In addition, the ultrafast excited-state dynamics of DCVJ in different solvents was also not unambiguous.…”