Abstract
Excited anthracene is well-known to photodimerize and not to exhibit excimer emission in isotropic organic solvents. Anthracene (AN) forms two types of supramolecular host-guest complexes (2:1 and 2:2, H:G) with the synthetic host octa acid in aqueous medium. Excitation of the 2:2 complex results in intense excimer emission, as reported previously, while the 2:1 complex, as expected, yields only monomer emission. This study includes confirming of host-guest complexation by NMR, probing the host-guest structure by molecular dynamics simulation, following the dynamics AN molecules in the excited state by ultrafast time-resolved experiments, and mapping of the excited surface through quantum chemical calculations (QM/MM-TDDFT method). Importantly, time-resolved emission experiments revealed the excimer emission maximum to be time dependent. This observation is unique and is not in line with the textbook examples of time-independent monomer-excimer emission maxima of aromatics in solution. The presence of at least one intermediate between the monomer and the excimer is inferred from time-resolved area normalized emission spectra. Potential energy curves calculated for the ground and excited states of two adjacent anthracene molecules via the QM/MM-TDDFT method support the model proposed on the basis of time-resolved experiments. The results presented here on the excited-state behavior of a well-investigated aromatic molecule, namely the parent anthracene, establish that the behavior of a molecule drastically changes under confinement. The results presented here have implications on the behavior of molecules in biological systems.
| Original language | English |
|---|---|
| Pages (from-to) | 2025-2036 |
| Number of pages | 12 |
| Journal | Journal of the American Chemical Society |
| Volume | 143 |
| Issue number | 4 |
| DOIs | |
| State | Published - Feb 3 2021 |
| Externally published | Yes |
Funding
V.R. and R.P. thank the National Science Foundation (CHE-1807729 and CHE-1664926) for financial support. P.S. thanks the Indian Institute of Technology Kanpur for infrastructure and financial support. A.D. acknowledges the Ministry of Electronics & Information Technology (MeitY), Government of India, for providing a fellowship under the Visvesvaraya Ph.D. scheme. S.B. and V.S. thank IISER Bhopal for providing high-performance computing facilities and funding. The support and the resources provided by the Centre for Develoment of Advanced Computing (C-DAC) and the National Supercomputing Mission (NSM), Government of India, are gratefully acknowledged.