Sayed Mhejabeen, Sundararajan Mahesh, Mohanty Jyotirmayee, Bhasikuttan Achikanath C, Pal Haridas
Radiation & Photochemistry Division and ‡Theoretical Chemistry Section, Chemistry Group, Bhabha Atomic Research Centre , Trombay, Mumbai 400085, India.
J Phys Chem B. 2015 Feb 19;119(7):3046-57. doi: 10.1021/jp509243j. Epub 2015 Jan 30.
Supramolecular host-guest interaction of cationic oxazine-1 (OX1) dye with two cucurbit[n]uril (CBn) hosts, namely, CB7 and CB8, has been investigated using photophysical and quantum chemical studies. Both CB7 and CB8 display much stronger binding affinities for OX1 dye compared to conventional cyclodextrin (CD) hosts, which arises due to strong ion-dipole interaction in stabilizing the dye-host inclusion complexes in the present systems. From photophysical studies supported by (1)H NMR results and quantum chemical calculations, it is inferred that 1:1 inclusion complexes are mainly formed in the present systems, though a small percentage of 1:2 (dye·host2) complexes are also indicated from time-resolved (TR) fluorescence studies. Longer rotational relaxation times for dye-CBn systems compared to the free dye as estimated from TR anisotropy studies support the inclusion complex formation in the present systems. The binding constant value is estimated to be significantly higher for the OX1-CB7 system than the OX1-CB8 system, and these results are in accordance with compatible portal diameter of CB7 cavity compared to the much larger portal diameter of CB8 cavity relative to the width of the OX1 molecule. Accordingly, CB7 cavity renders a relatively stronger binding than the CB8 cavity for an axially incorporated OX1 dye into the host cavity. Results from the quantum chemical calculations are overall supportive to the inferences drawn from photophysical measurements. Observed results clearly suggest that the dimensions of the CBn cavities play an important role in determining the interaction strength and stoichiometry of the host-guest complexes formed and thus bring out significant changes in the photophysical properties of the bound dye. The host-assisted modulation in the photophysical properties of the dye, as observed in the present study, has a direct relevance to applications like aqueous dye lasers, sensors, fluorescence assays, and so on.
通过光物理和量子化学研究，对阳离子恶嗪 -1（OX1）染料与两种葫芦[n]脲（CBn）主体，即CB7和CB8之间的超分子主客体相互作用进行了研究。与传统的环糊精（CD）主体相比，CB7和CB8对OX1染料均表现出更强的结合亲和力，这是由于在本体系中稳定染料 - 主体包合物时存在强离子 - 偶极相互作用。根据（1）H NMR结果支持的光物理研究和量子化学计算推断，本体系中主要形成1:1包合物，不过时间分辨（TR）荧光研究也表明存在少量1:2（染料·主体2）络合物。从TR各向异性研究估计，与游离染料相比，染料 - CBn体系具有更长的旋转弛豫时间，这支持了本体系中包合物的形成。据估计，OX1 - CB7体系的结合常数比OX1 - CB8体系高得多，这些结果与CB7腔的孔径与CB8腔相比与OX1分子宽度更兼容相一致。因此，对于轴向掺入主体腔中的OX1染料，CB7腔比CB8腔表现出相对更强的结合力。量子化学计算结果总体上支持从光物理测量得出的推论。观察结果清楚地表明，CBn腔的尺寸在决定形成的主客体络合物的相互作用强度和化学计量方面起着重要作用，从而使结合染料的光物理性质发生显著变化。如本研究中所观察到的，主体对染料光物理性质的辅助调节与诸如水性染料激光器、传感器、荧光测定等应用直接相关。
