通过稳态和超快光谱研究了解推拉二甲氨基-苯基乙炔基苯基-二氰基咪唑的分子内电荷转移动力学,The Journal of Physical Chemistry C

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通过稳态和超快光谱研究了解推拉二甲氨基-苯基乙炔基苯基-二氰基咪唑的分子内电荷转移动力学
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2023-02-22 , DOI: 10.1021/acs.jpcc.2c08320
Haraprasad Mandal ₁ , J. Laxmikanth Rao ₂ , Jiří Kulhánek ₃ , Filip Bureš ₃ , Prakriti Ranjan Bangal ₁

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D−π–A化合物2-{4-[4-( N , N-二甲基氨基)苯乙炔基]苯基-1-甲基-1H的光物理行为-imidazole-4,5-dicarbonitrile (DMAPPIDCN) 在室温下使用稳态吸收、荧光发射和飞秒时间分辨吸收和发射光谱技术以及计算时间相关密度泛函理论 (TD-DFT) 计算进行了探索. 光谱研究在不同极性的不同溶剂中进行，包括二元溶剂混合物。溶剂极性、粘度和温度对 DMAPPIDCN 松弛机制的作用被公开。观察到的稳态和时间分辨光谱特征归因于分子内电荷转移 (ICT) 动力学。_{DMAPPIDCN 中的 ICT 被合理化为 N(CH 3} ) ₂和整个N的顺序扭曲运动，分子轴周围的N -二甲氨基苯基部分连接相邻的咪唑苯基部分，导致 TICT ₁和 TICT ₂ (σ*) 态。增加的溶剂极性主要影响荧光发射光谱，表明激发态偶极矩显着增加。这一结果清楚地揭示了 TICT ₂ (σ*) 的形成，涉及从 ( N , N - 二甲基氨基) 苯基 (DMAP) 供体到苯基-1-甲基-1 H -咪唑-二腈 (PIDCN) 受体的有效电荷转移极地环境中的激发态。在 TICT ₂(σ*) 状态下，吸电子和给电子部分的平面垂直于角度 (DMAP)C–C≡C 为 141.1°。这种非平面排列解释了观察到的大斯托克斯位移。时间分辨荧光光谱研究揭示了激发态弛豫过程，证实了非质子介质中的非辐射衰减率随着溶剂介电常数的增加而增加。飞秒瞬态光谱研究明确证实了分离良好的 LE 和 TICT 状态的存在及其在极地介质中的后续动力学。在非极性溶剂中，DMAPPIDCN 显示出从 LE (ππ*) 态发出的强荧光，而在极性溶剂中，

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Understanding of Intramolecular Charge Transfer Dynamics of a Push–Pull Dimethylamino-phenylethynylphenyl-dicyanoimidazole by Steady-State and Ultrafast Spectroscopic Studies

Photophysical behaviors of D−π–A compound 2-{4-[4-(N,N-dimethylamino)phenylethynyl]phenyl-1-methyl-1H-imidazole-4,5-dicarbonitrile (DMAPPIDCN) were explored using steady-state absorption, fluorescence emission, and femtosecond time-resolved absorption and emission spectroscopic techniques at room temperature along with computational time-dependent density functional theory (TD-DFT) calculation. The spectroscopic studies were carried out in different solvents of varying polarities including binary solvent mixtures. The role of the solvent polarity, viscosity, and temperature on the relaxation mechanism of DMAPPIDCN is disclosed. The observed steady-state and time-resolved spectroscopic features were attributed to intramolecular charge transfer (ICT) dynamics. The ICT in DMAPPIDCN is rationalized to a sequential twisted motion of both N(CH₃)₂ and whole N,N-dimethylaminophenyl moieties around the molecular axis interconnecting the adjacent imidazolephenyl moiety leading to the TICT₁ and TICT₂ (σ*) states. The increased solvent polarity affected mostly the fluorescence emission spectra pointing to a significant increase in the excited state dipole moment. This result clearly reveals formation of the TICT₂ (σ*) involving efficient charge transfer from the (N,N-dimethylamino)phenyl (DMAP) donor to the phenyl-1-methyl-1H-imidazole-dicarbonitrile (PIDCN) acceptor in the excited state in a polar environment. In the TICT₂ (σ*) state, the planes of electron-withdrawing and electron-donating moieties are perpendicular with the angle (DMAP)C–C≡C being 141.1°. This nonplanar arrangement accounts for the observed large Stokes shift. Time-resolved fluorescence spectroscopic studies unveil the excited state relaxation processes confirming the increase in the nonradiative decay rate in aprotic medium with increase in the solvent dielectric constants. Femtosecond transient spectroscopic studies unambiguously confirmed the existence of well separated LE and TICT states and their ensuing kinetics in polar medium. In nonpolar solvents, DMAPPIDCN shows strong fluorescence which emits from the LE (ππ*) state, whereas in polar solvents, formation of two consecutive TICT states occurs from the LE (ππ*) in a sub picosecond to few picosecond time domain depending on polarity of the solvents and the non-radiative decay from the TICT states.

更新日期：2023-02-22

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