216 research outputs found
Time-Dependent Density Matrix Renormalization Group Algorithms for Nearly Exact Absorption and Fluorescence Spectra of Molecular Aggregates at Both Zero and Finite Temperature
We implement and apply time-dependent density matrix renormalization group
(TD-DMRG) algorithms at zero and finite temperature to compute the linear
absorption and fluorescence spectra of molecular aggregates. Our implementation
is within a matrix product state/operator framework with an explicit treatment
of the excitonic and vibrational degrees of freedom, and uses the locality of
the Hamiltonian in the zero-exciton space to improve the efficiency and
accuracy of the calculations. We demonstrate the power of the method by
calculations on several molecular aggregate models, comparing our results
against those from multi-layer multiconfiguration time- dependent Hartree and
n-particle approximations. We find that TD-DMRG provides an accurate and
efficient route to calculate the spectrum of molecular aggregates.Comment: 10 figure
Quantum Dynamical Approach to Predicting the Optical Pumping Threshold for Lasing in Organic Materials
We present a quantum dynamic study on organic lasing phenomena, which is a
challenging issue in organic optoelectronics. Previously, phenomenological
method has achieved success in describing experimental observation. However, it
cannot directly bridge the laser threshold with molecular electronic structure
parameters and cavity parameters. Quantum dynamics method for describing
organic lasing and obtaining laser threshold is highly expected. In this
Letter, we first propose a microscopic model suitable for describing the lasing
dynamics of organic molecular system and we apply the time-dependent
wave-packet diffusion (TDWPD) to reveal the microscopic quantum dynamical
process for the optical pumped lasing behavior. Lasing threshold is obtained
from the onset of output as a function of optical input pumping. We predict
that the lasing threshold has an optimal value as function of the cavity volume
and depends linearly on the intracavity photon leakage rate. The
structure-property relationships between molecular electronic structure
parameters (including the energy of molecular excited state, the transition
dipole and the organization energy) and the laser threshold obtained through
numerical calculations are in qualitative agreement the experimental results,
which also confirms the reliability of our approach. This work is beneficial to
understanding the mechanism of organic laser and optimizing the design of
organic laser materials. TO
General Approach To Compute Phosphorescent OLED Efficiency
Phosphorescent organic light-emitting diodes (PhOLEDs) are widely used in the
display industry. In PhOLEDs, cyclometalated Ir(III) complexes are the most
widespread triplet emitter dopants to attain red, e.g., Ir(piq)3 (piq =
1-phenylisoquinoline), and green, e.g., Ir(ppy)3 (ppy = 2-phenylpyridine),
emissions, whereas obtaining operative deep-blue emitters is still one of the
major challenges. When designing new emitters, two main characteristics besides
colors should be targeted: high photostability and large photoluminescence
efficiencies. To date, these are very often optimized experimentally in a
trial-and-error manner. Instead, accurate predictive tools would be highly
desirable. In this contribution, we present a general approach for computing
the photoluminescence lifetimes and efficiencies of Ir(III) complexes by
considering all possible competing excited-state deactivation processes and
importantly explicitly including the strongly temperature-dependent ones. This
approach is based on the combination of state-of-the-art quantum chemical
calculations and excited-state decay rate formalism with kinetic modeling,
which is shown to be an efficient and reliable approach for a broad palette of
Ir(III) complexes, i.e., from yellow/orange to deep-blue emitters
Emerging technologies for a more sustainable future
Preface for emerging technologies and new directions in chemistry researc
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