The crown thioether 9-[4-(4,7,10,13-tetrathia-1-azacyclopentadecyl]phenyl-N-methylacridinium perchlorate (TCMA) was synthesized and characterized with the aim to verify its ability to interact selectively with metal ions and substantiate the possibility to detect easily the presence of heavy metals in fluid samples. The spectroscopic properties of TCMA, alone and in the presence of metal ions, were therefore studied in polar solvents (MeCN and H2O); in particular, steady-state UV-Vis spectrophotometric and fluorimetric techniques were used together with transient absorption spectroscopy with fs time resolution to investigate the spectral and dynamic properties of the lowest excited singlet state of TCMA and of TCMA/metal ion complexes. The absorption in the Vis region is characterized by a charge-transfer nature with the methylacridinium moiety acting as the electron-acceptor and the anilic group as the electron-donor. No emission from the S1 was detected both in MeCN and H2O, while a small S2 → S0 fluorescence emission (λmax = 485 nm and ϕF = 0.0011) was detected in water. Time-resolved measurements with fs resolution of TCMA in MeCN have shown that the relaxed S1 state is reached ∼0.6 ps after the laser pulse, while the S1 → S0 time constant is 3.7 ps. Among the investigated metal ions, only Fe3+ (in MeCN) and Hg2+ (in MeCN and H2O) were able to form stable complexes (association constant, Kass = 1–11 × 104 M−1) with TCMA. The S1 state of the TCMA/Mn+ complexes emits with low quantum yield (ϕF = 0.0023–0.014) and decays with time constants much longer than TCMA itself, at least in the case of TCMA/Hg2+ in MeCN. This study showed that TCMA is a good candidate for colorimetric/fluorimetric sensing of Hg2+ in aqueous media owing to its high selectivity towards metal ions.
合冠
硫醚9-[4-(4,7,10,13-四
硫-1-氮杂环戊
十五烷)苯基]-N-甲基acridinium
高氯酸盐(TCMA)被合成并表征,旨在验证其选择性与
金属离子相互作用的能力,并证实在流体样本中轻松检测重
金属存在的可能性。因此,TCMA在极性溶剂(MeCN和
H2O)中,单独及在
金属离子存在下的光谱特性进行了研究;特别是,使用了稳态UV-Vis光谱法和荧光测定技术,并结合飞秒时间分辨率的瞬态吸收光谱法,研究了TCMA及其与
金属离子形成的复合物的最低激发单态的光谱和动态特性。可见光区域的吸收具有电荷转移特性,N-甲基acridinium部分作为电子受体,而邻
氨基部分作为电子供体。在MeCN和 中都未检测到S1态的发射,但在
水中检测到少量的S2 → S0荧光发射(λMAx = 485 nm,ϕF = 0.0011)。在MeCN中对TCMA进行的飞秒分辨率的时间分辨测量表明,松弛的S1态在激光脉冲后约0.6 ps内达到,而S1 → S0的时间常数为3.7 ps。在调查的
金属离子中,仅有Fe3+(在MeCN中)和Hg2+(在MeCN和 中)能够与TCMA形成稳定的复合物(结合常数Kass = 1–11 × 10⁴ M⁻¹)。TCMA/Mn+复合物的S1态发射量子产率较低(ϕF = 0.0023–0.014),其衰变的时间常数远长于TCMA自身,至少在TCMA/Hg2+的MeCN情况下如此。这项研究表明,由于其对
金属离子的高选择性,TCMA是
水介质中Hg2+比色法/荧光法检测的良好候选物。