10.1002/cphc.202000612
ChemPhysChem
ARTICLE
dielectric constant of 2.38, typical values for a toluene. Suitable molecules
from ground state QMD are sampled to perform first excited state QMD
using time dependent LC-ωPBE at same basis level. In order to establish
the relevance to the experimental observations, the vertical absorption
oscillatory strengths along with the probability densities of that particular
orientations needed to be taken account. Hence, the mapping of Figure
6(a) is reduced from 50 x 50 matrix to 10 x 10 matrix and the products of
vertical absorption oscillatory strengths and the probability densities, p,
were calculated (see Table S2-S5 in supplementary information). The
molecules with the highest product, pmax and up to 0.1pmax were selected
for excited state QMD. Time-reversible integrator with dissipation is also
implemented. The relevant data points are then extracted from the output
files so that intermolecular distance and the angle formed by the two
normal vectors defined in the manuscript can be calculated using Python
3.5 with the help of numpy and sympy modules. For initial configuration for
molecular dynamics simulations of 10:10:60 molecules of
TPA:TRZ:toluene and pTPA:TRZ:toluene were randomly distributed in the
simulation box of 80.6 x 84.9 x 77.3 Å3 using a Packmol Program [40].
CHARMM force field and conjugate gradient algorithm were applied to
optimize the energy until the convergence of 0.01 kcal/(Å mol) was
obtained using HyperChem software. Series of molecular dynamics
simulations were done using NVT ensemble. In the heating phase of 200
ps with 1 fs time step, the temperature of the system is increased from an
initial value of 0 K to a final value of 300 K with temperature step of 10 K.
Then, each system was kept at 300 K for another 400 ps using time step
of 2 fs and the final complex structure was obtained for interaction analysis.
Conclusion
The formation of heterodimer between TPA and TRZ is
encouraged by the interaction between partial localization of 2pz
electrons in the nitrogen atom of TPA and π electron deficient in
triazine and the π-π stacking interactions between phenyl groups.
However, such interactions can be destroyed by introducing tert-
butyl group as a bulky side groups at para- position in TPA. The
weakly bounded heterodimers formed between pTPA and TRZ
adopt numerous conformational configurations in solvent in
contrast to TPA-TRZ, with only one dominant conformer is found
in QMD. As a result, emission from pTPA-TRZ heterodimers
consist of numerous superimposed Gaussian peaks. One of the
important implications that we can infer from such system,
because of strong coulombic interaction between hole and
electron in donor-acceptor system in the excited state,
intermolecular distance is expected to reduce when there is
sufficient face to face stacking between donors and acceptors.
This will be accompanied by geometry relaxation after de-
excitation contributing the loss of energy via molecular
reorganizations in particularly if flexible bonds are connected
between them.
Experimental Section
Conflicts of interest
Characterization and measurements. Materials were characterized by
means of 1H and 13C NMR spectroscopy using BRUKER AVN III 400 MHz
FT-NMR spectrometer using deuterated chloroform as the solvent and
TMS as internal standard.
There are no conflicts to declare
Acknowledgements
Material Synthesis. Tris-(4-tert-butylphenyl)amine was synthesized using
Friedel-Crafts alkylation reaction according to literature procedure [36].
Trifluoroacetic acid can be used for activation of tert-butyl alcohol. A
mixture of triphenylamine (0.5 g), 2-methylpropane-2-ol (2 mL), and
trifluoroacetic acid (10 mL) was stirred and refluxed for 24h. Then, the
mixture was poured in 20% NaOH solution and the aqueous layer was
extracted with dichloromethane. The organic layer was dried, filtered and
the solvent was removed under vacuum. The precipitated was subjected
to column chromatography using 100% heptane. The resulting white solid
collected has a mass of 0.5865g (69 % yield). 1H NMR (400 MHz, CDCl3):
δ 1.31 (s, 27H; C-(CH3)3), 7.01 (d, J = 8.8 Hz, 6H; Ar-H), 7.24 (d, J = 8.8
Hz, 6H; Ar-H), 13C NMR (100 MHz, CDCl3): σ=31.7 [(C-(CH3)3], 34.4 (C),
123.6 (Ar-CH), 126.1 (Ar-CH), 145.2 (Ar-C), 145.5 (Ar-C).
The authors gratefully acknowledge the funding by the University
Malaya Research University Grant-Faculty Program (GPF046B-
2018) and Dr. Hadieh Monajemi and Kheng Ghee Ng from Data
Intensive Computing Centre of University Malaya for rentlessly
maintaining the GPU servers. Also, the authors would like to thank
Dr. Muhammad Faisal Bin Khyasudeen for the technical
discussion.
Keywords: dimer• donor • acceptor • TADF • conformer
References
Photophysical properties. The UV-visible absorption spectra of the
compounds in solutions of toluene at a concentration of 100 µM was
observed using a Shimadzu UV-Vis spectrophotometer (UV-2600). The
photoluminescence emission spectra of the compounds in solutions of
cyclohexane and toluene at room temperature were characterized using a
Perkin Elmer luminescence spectrophotometer with 325nm excitation
wavelength.
[1]
N. Hayashi, A. Kanda, H. Higuchi, K. Ninomiya in Topics in Heterocyclic
Chemistry, Vol. 18 (Eds.: K. Matsumoto, N. Hayashi), Springer, 2009,
pp. 1-35.
[2]
[3]
Y. S. Wang, J. Yang, Y. Tian, M. M. Fang, Q. Y. Liao, L. W. Wang, W.
P. Hu, B. Tang, Z. Li, Chem Sci 2020, 11, 833-838.
M. K. Etherington, N. A. Kukhta, H. F. Higginbotham, A. Danos, A. N.
Bismillah, D. R. Graves, P. R. McGonigal, N. Haase, A. Morherr, A.
Batsanov, C. Pflumm, V. Bhalla, M. R. Bryce, A. P. Monkman, J Phys
Chem C 2019, 123, 11109-11117.
Computational calculations. All molecular geometries are optimized
using density functional calculations performed in Terachem 1.9 [37] using
the optimally tuned range-separated [38] LC-ωPBE functional at cc-pVDZ
basis level under polarizable continuum model (PCM) with toluene as a
solvent [39]. The calculations were performed using a GPU server that had
64 GB RAM installed to support eight Tesla K10 graphic cards. The
optimized geometries are then subjected to quantum molecular dynamics
(QMD) simulations using the same functional theory except at 6-31g basis
set. The initial temperature is set at 550K with equilibrium temperature of
300K using Langevin as a thermostat. Langevin is chosen to simulate the
effect of jostling of solvents. The QMDs are carried out with 1 femtosecond
(fs) time step with 100000 steps. The solvent radius is set to be 3.48 Å and
[4]
K. L. Woon, Z. A. Hasan, B. K. Ong, A. Ariffin, R. Griniene, S.
Grigalevicius, S. A. Chen, Rsc Adv 2015, 5, 59960-59969.
V. Jankus, A. P. Monkman, Adv Funct Mater 2011, 21, 3350-3356.
B. Feringan, P. Romero, J. L. Serrano, C. L. Folcia, J. Etxebarria, J.
Ortega, R. Termine, A. Golemme, R. Gimenez, T. Sierra, J Am Chem
Soc 2016, 138, 12511-12518.
[5]
[6]
[7]
[8]
M. Carini, M. Marongiu, K. Strutynski, A. Saeki, M. Melle-Franco, A.
Mateo-Alonso, Angew Chem Int Edit 2019, 58, 15788-15792.
Z. H. Zong, P. Z. Li, A. Y. Hao, P. Y. Xing, J Phys Chem Lett 2020, 11,
4147-4155.
6
This article is protected by copyright. All rights reserved.