Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India.
J Phys Chem B. 2020 Apr 2;124(13):2668-2675. doi: 10.1021/acs.jpcb.0c00954. Epub 2020 Mar 23.
Compounds possessing two fluorophoric moieties may exhibit dual fluorescence, one characterizing the monomeric fluorophore unit and the other characterizing the intramolecular aggregate. Fluorescence quenching of two dipyrenylalkanes, 1,3-bis(1-pyrenyl)propane [1Py(3)1Py] and 1,10-bis(1-pyrenyl)decane [1Py(10)1Py] having different alkyl chains separating the two termini pyrenyl groups that are capable of forming an intramolecular excimer, by an electron/charge-accepting quencher, nitromethane, is investigated in four different solvents-nonpolar (cyclohexane (CH)), polar-aprotic (acetonitrile (ACN)), polar-protic (ethanol (EtOH)), and chlorinated (dichloromethane (DCM))-under ambient conditions. For a given probe in a solvent, fluorescence from the monomer and the intramolecular excimer are quenched with similar efficiencies; the efficiency of quenching is higher for the probe with the longer alkyl chain separating the two fluorophores. Quenching efficiency is significantly higher in chlorinated solvent DCM. The bimolecular quenching rate constants for intramolecular excimer, however, are either comparable or lower for the longer alkyl chain compound. It is suggested that, while the donor electronic excited-state energetics is more favorable for the long alkyl chain compound, the approach of the quencher to the intramolecular excimer appears to be hindered by the presence of a longer alkyl chain.
具有两个荧光团的化合物可能表现出双重荧光，一种特征是单体荧光团单元，另一种特征是分子内聚集体。在四种不同溶剂（非极性（环己烷（CH））、极性无质子（乙腈（ACN））、极性质子（乙醇（EtOH））和氯化（二氯甲烷（DCM）））中，通过电子/电荷接受猝灭剂硝基甲烷，研究了具有不同烷基链的两个末端芘基基团能够形成分子内激基的两个二芘基烷烃，1,3-双（1-芘基）丙烷[1Py（3）1Py]和 1,10-双（1-芘基）癸烷[1Py（10）1Py]的荧光猝灭。在给定溶剂中的给定探针下，单体和分子内激基的荧光猝灭效率相似；分离两个荧光团的烷基链较长的探针的猝灭效率更高。在氯化溶剂 DCM 中，猝灭效率显着更高。然而，对于较长的烷基链化合物，分子内激基的双分子猝灭速率常数要么相当，要么更低。有人认为，虽然供体电子激发态的能量更有利于长链烷基化合物，但猝灭剂接近分子内激基的过程似乎受到长链烷基的阻碍。
