Kournoutas Fotis, Seintis Kostas, Karakostas Nikolaos, Tydlitát Jiří, Achelle Sylvain, Pistolis George, Bureš Filip, Fakis Mihalis
Department of Physics , University of Patras, Greece , GR-26504 Patras , Greece.
NCSR "Demokritos" Institute of Nanosciences and Nanotechnology (INN) , 153 10 Athens , Greece.
J Phys Chem A. 2019 Jan 17;123(2):417-428. doi: 10.1021/acs.jpca.8b08628. Epub 2019 Jan 7.
A comparative study of the photophysical properties of octupolar pyridyl-terminated triphenylamine molecule, with its quadrupolar and dipolar analogues, by means of ambient and low temperature steady state spectroscopy and femtosecond to nanosecond time-resolved fluorescence spectroscopy is reported. The push-pull molecules bear triphenylamine electron donating core, pyridine peripheral electron acceptors, and acetylene π-bridge. The samples were studied in solvents of varying polarity and also upon addition of small amounts of acetic acid to induce protonation of the pyridine group. All samples exhibit significant positive fluorescence solvatochromism as well as a relaxation of their excited state to a solvent relaxed intramolecular charge transfer state on the picosecond time scale. For the octupolar compound, excited state relaxation occurs simultaneously with excitation energy hopping among the branches. The hopping time is solvent polarity controlled since it becomes slower as the polarity increases. The experimental hopping times are compared to those predicted by Förster and Fermi formulations. The samples are capable of emitting broadband light covering almost the whole visible spectrum by careful control of protonation. Energy transfer from the neutral toward the protonated species on the 1 ps time scale is revealed.
报道了通过环境和低温稳态光谱以及飞秒到纳秒时间分辨荧光光谱，对八极吡啶基封端的三苯胺分子及其四极和偶极类似物的光物理性质进行的比较研究。推拉分子带有三苯胺给电子核心、吡啶外围电子受体和乙炔π桥。在不同极性的溶剂中以及加入少量乙酸以诱导吡啶基团质子化后对样品进行了研究。所有样品均表现出显著的正荧光溶剂化显色现象，并且在皮秒时间尺度上其激发态弛豫到溶剂弛豫的分子内电荷转移态。对于八极化合物，激发态弛豫与分支之间的激发能跳跃同时发生。跳跃时间受溶剂极性控制，因为随着极性增加它会变慢。将实验跳跃时间与福斯特和费米公式预测的时间进行了比较。通过仔细控制质子化，样品能够发射覆盖几乎整个可见光谱的宽带光。揭示了在1皮秒时间尺度上从中性物种向质子化物种的能量转移。
