What Is the Optoelectronic Effect of the Capsule on the Guest Molecule in Aqueous Host/Guest Complexes? A Combined Computational and Spectroscopic Perspective

Abstract

Encapsulation of dye molecules is used as a means to achieve charge separation across different dielectric environments. We analyze the absorption and emission spectra of several coumarin molecules that are encapsulated within an octa-acid dimer forming a molecular capsule. The watersolvated capsule effect on the coumarin's electronic structure and absorption spectra can be understood as due to an effective dielectric constant where the capsule partially shields electrostatically the dielectric solvent environment. Blueshifted emission spectra are explained as resulting from a partial intermolecular charge transfer where the capsule is the acceptor, and which reduces the coumarin relaxation in the excited state.

Marcus Relationship Maintained During Ultrafast Electron Transfer Across a Supramolecular Capsular Wall

“…The modeled structure shown in the Supporting Information (Figure S3) is consistent with the NMR spectra mentioned above (Figure ). (f) Quantum chemical calculations employing the time-dependent density functional theory using the polarizable continuum model carried out earlier suggest that the OA capsule acts as a charge acceptor upon excitation of the encapsulated C153 . Apparently, upon excitation, the electron density shifts from C153 to the wall.…”

“…We have recently demonstrated the occurrence of photoinduced electron transfer (PET) between OA-encapsulated donors [stilbene, coumarins, and azulenes (Az’s)] and methyl viologen acceptor in phosphate/borate buffer solution (pH ∼ 7.4 and 8.7). − Through time-resolved experiments, we have identified the formation of methyl viologen radical cation as well as stilbene radical cation, the products of electron transfer. With the help of ultrafast time-resolved experiments, the forward electron transfers were found to occur with time constants between 1 and 25 ps.…”

Fluorescent-Cavity Host: An Efficient Probe to Study Supramolecular Recognition Mechanisms

“…Conjugated materials with various light-emitting properties are constantly being developed and exploited in various applications, e.g., organic light-emitting diodes, sensors, color tunable emitters, cell imaging agents, photoresponsive materials, etc. − Incorporating conjugated fragments into a supramolecular system has gained considerable interest because of tunability, responsiveness to stimuli, and the ease of constituting building blocks bearing a wide range of functionality. − In particular, merging conjugated structures and the macrocyclic hosts has been achieved by (1) binding conjugated guests to hosts, − (2) synthesizing fully conjugated macrocycles, , (3) attaching macrocyclic hosts onto a conjugated backbone as pendant groups, − or (4) incorporating macrocycles into the conjugated structure. − The last approach, i.e., the strategy adopted here, may affect the volume, rigidity, and electrostatic potential of the host cavity and, consequently, could tune the photophysical properties and the host–guest interactions. Specifically, pillar[5]­arene, a promising class of macrocycles, was chosen for making the conjugated hosts because of its ease of synthesis and functionalization. − Although few conjugated pillararenes have been reported, none of the studies took advantage of the fluorescence signals for the evaluation of the host–guest recognition mechanism. − …”

Electronic Spectra of C60 Films Using Screened Range Separated Hybrid Functionals

“…PCM − is highly effective in representing the dielectric environment effects on the electronic structure of a single molecule at the condensed phase. In particular, PCM invoked with RSH functionals, − which are designed to achieve physically meaningful orbital gaps, can be used to describe well charge transport properties. PCM-affected calculations were shown to achieve impressive success in representing the gap of condensed-phase systems. ,,,− RSH-PCM has also been employed within TDDFT calculations of condensed-phase excited state energies. , More recently, the SRSH-PCM framework that offers a polarization consistent procedure was used in TDDFT calculations in benchmarking states energies of solvated donor–acceptor complex , and in studies of various pigments. ,, Below, SRSH-PCM is used to affect the thin film environment in single C 60 and dimer-based TDDFT calculations of the electronic excited states.…”

“…16,35,36,49−53 RSH-PCM has also been employed within TDDFT calculations of condensedphase excited state energies. 48,52 More recently, the SRSH-PCM framework that offers a polarization consistent procedure was used in TDDFT calculations in benchmarking states energies of solvated donor−acceptor complex 37,38 and in studies of various pigments. 33,34,54 Below, SRSH-PCM is used to affect the thin film environment in single C 60 and dimerbased TDDFT calculations of the electronic excited states.…”