4 research outputs found
Quantum Dynamics Simulations Reveal Vibronic Effects on the Optical Properties of [<i>n</i>]Cycloparaphenylenes
The size-dependent ultraviolet/visible
photophysical property trends
of [<i>n</i>]Âcycloparaphenylenes ([<i>n</i>]ÂCPPs, <i>n</i> = 6, 8, and 10) are theoretically investigated using quantum
dynamics simulations. For geometry optimizations on the ground- and
excited-state Born–Oppenheimer potential energy surfaces (PESs),
we employ density functional theory (DFT) and time-dependent DFT calculations.
Harmonic normal-mode analyses are carried out for the electronic ground
state at Franck–Condon geometries. A diabatic Hamiltonian,
comprising four low-lying singlet excited electronic states and 26
vibrational degrees of freedom of CPP, is constructed within the linear
vibronic coupling (VC) model to elucidate the absorption spectral
features in the range of 300–500 nm. Quantum nuclear dynamics
is simulated within the multiconfiguration time-dependent Hartree
approach to calculate the vibronic structure of the excited electronic
states. The symmetry-forbidden <i>S</i><sub>0</sub> → <i>S</i><sub>1</sub> transition appears in the longer wavelength
region of the spectrum with weak intensity due to VC. It is found
that the Jahn–Teller and pseudo-Jahn–Teller effects
in the doubly degenerate <i>S</i><sub>2</sub> and <i>S</i><sub>3</sub> electronic states are essential in the quantitative
interpretation of the experimental observation of a broad absorption
peak around 340 nm. The vibronic mixing of the <i>S</i><sub>1</sub> state with higher electronic states is responsible for the
efficient photoluminescence from the <i>S</i><sub>1</sub> state. The fluorescence properties are characterized on the basis
of the stationary points of the excited-state PESs. The findings reveal
that vibronic effects become important in determining the photophysical
properties of CPPs with increased ring size
A π‑Conjugated System with Flexibility and Rigidity That Shows Environment-Dependent RGB Luminescence
We have designed and synthesized
a π-conjugated system that
consists of a flexible and nonplanar π joint and two emissive
rigid and planar wings. This molecular system exhibits respectively
red, green, and blue (RGB) emission from a single-component luminophore
in different environments, namely in polymer matrix, in solution,
and in crystals. The flexible unit gives rise to a dynamic conformational
change in the excited state from a nonplanar V-shaped structure to
a planar structure, leading to a dual fluorescence of blue and green
colors. The rigid and planar moieties favor the formation of a two-fold
Ï€-stacked array of the V-shaped molecules in the crystalline
state, which produces a red excimer-like emission. These RGB emissions
are attained without changing the excitation energy
A π‑Conjugated System with Flexibility and Rigidity That Shows Environment-Dependent RGB Luminescence
We have designed and synthesized
a π-conjugated system that
consists of a flexible and nonplanar π joint and two emissive
rigid and planar wings. This molecular system exhibits respectively
red, green, and blue (RGB) emission from a single-component luminophore
in different environments, namely in polymer matrix, in solution,
and in crystals. The flexible unit gives rise to a dynamic conformational
change in the excited state from a nonplanar V-shaped structure to
a planar structure, leading to a dual fluorescence of blue and green
colors. The rigid and planar moieties favor the formation of a two-fold
Ï€-stacked array of the V-shaped molecules in the crystalline
state, which produces a red excimer-like emission. These RGB emissions
are attained without changing the excitation energy
Dimerization-Initiated Preferential Formation of Coronene-Based Graphene Nanoribbons in Carbon Nanotubes
We have investigated the growth mechanism of coronene-derived
graphene
nanoribbons (GNRs) using two different precursors: coronene and a
dimer form of coronene, so-called dicoronylene (C<sub>48</sub>H<sub>20</sub>). For both of the precursors, the formation of nanoribbon-like
materials inside carbon nanotubes (CNTs) was confirmed by transmission
electron microscope observations. Experimental and theoretical Raman
analysis reveals that the samples also encapsulated dicoronylene and
linearly condensed other coronene oligomers, which can be regarded
as analogues to GNRs. Interestingly, it was found that the present
doping condition of coronene yields dicoronylene prior to encapsulation
due to the thermal dimerization of coronene. These results indicate
that the dimerization before the encapsulation drives the preferential
formation of the coronene-based GNRs within CNTs