Dear Editor and Referee,
We would like to submit the enclosed manuscript entitled ”Highly
stable binary cross-linkable organic nonlinear optical materials using
different acceptors based on Huisgen cycloaddition reaction ” which we
wish to be considered for publication in Chinese Journal
of Chemistry. The work described has not been submitted elsewhere for
publication, in whole or in part, and all the authors listed have
approved the manuscript that is enclosed.
Driven by emerging technologies such as 5G wireless communication, big
data, artificial intelligence/machine learning (AI/ML), cloud services,
telemedicine and autonomous vehicle, and the demand for telework caused
by the COVID-19, the world has experienced an explosive growth in
Internet data traffic. Information processing and transmission materials
based on photons have shown broad application prospects. At present,
lithium niobate (LiNbO3) is the commercialized
electro-optic material in electro-optic modulator. However, this kind of
material has some disadvantages, such as low electro-optic coefficient
（<30 pm/V） and large device size. With the development of
organic materials, many organic chromophore materials with super large
electro-optic coefficients (>1000pm/V) have been developed.
However, the application of organic nonlinear optical materials to
commercial electro-optic modulators and other fields also faces
technical bottlenecks (difficult to meet the Telecommunications
GR-468-CORE standards). How to obtain organic electro-optic chromophores
with both large electro-optic coefficients (r33 values),
photothermal stability, and polarization orientation stability is still
a challenge for the industry. In order to solve the above problem,
Crosslinked materials are the most promising solution to the stability
of organic electro-optical materials. However, there were few reports on
cross-linked electro-optic materials. Traditional high
Tg polymeric cross-linked OEO systems have chromophore
number density ρN usually less than ∼2.7 ×
1020 molecules/cm3 and
r33 value usually less than 150 pm/V. We have developed
binary crosslinkable chromophores HLD1/HLD2 (Chem. Mater. 2020, 32,
1408−1421) and QLD1/QLD2 (Chem. Sci., 2022, 13, 13393–13402) with 100
wt% chromophores for the first time, resulting in significant increase
in the electro-optic coefficient to 290-327pm/V and glass transition
temperature as high as 174-185 ℃.HLD1/HLD2 has been successfully applied
to many advanced optoelectronic devices (Nature Electronics 2020, 3,
(6), 338-345, Nano Lett. 2021, 21, 4539−4545 and so on). In addition,
the United States and Europe have also set up corresponding companies to
produce HLD1/HLD2 and related optoelectronic devices.
However, the crosslinking method of HLD1-2 and QLD1-2 is limited to the
Diels-Alder reaction of anthracene and acrylate. This reaction requires
60 minutes of reaction at 160 degrees celsius to complete crosslinking.
Excessive temperature and longer reaction time may cause the
decomposition of chromophores and the waste of energy. So it is very
important to develop new cross-linkable groups suitable for binary
cross-linked chromophores. And there is still a lack of systematic
research on pure chromophore crosslinking systems: For this reason, we
proposed a systematic research idea of binary cross-linked chromophores:
Azide and alkyne were introduced into the donor and bridge parts of
tetrahydroquinoline derivatived chromophores TLD1 and TLD2 .
After the chromophore molecules undergo poling orientation, the
temperature continues to rise, and the molecules undergo Huisgen
cycloaddition at 150 ℃ to form a polymer network, greatly improving the
long-term alignment stability of the materials.Electro-optic coefficient
up to 312 pm/V and glass transition temperature as high as 152 ℃was
achieved in these cross-linked film due to high chromophore density
(5.58× 1020 molecules/cm3) and large
hyperpolarizability.
In order to further improve the glass transition temperature and optical
transparency of the material. We introduced the 5Fph-TCF acceptor into
the binary crosslinking system for the first time. The chromophores TLD3
and TLD4 using 5Fph-TCF as acceptor exhibit higher glass transition
temperatures and better optical transparency
The glass transition temperatures of chromophores TLD3-4 was 104 and
118℃, respectively, which was much higher than the 85 and 57 ℃ of
chromophore TLD1-2, respectively. The glass transition temperature of
cross-linked TLD3/TLD4 was as high as 174 ℃, which was also 22 ℃ higher
than that of cross-linked TLD1-2. In addition, compared to chromophore
TLD1-2, the UV absorption wavelength of chromophore TLD3-4 has blue
shifted by ~40 nm, demonstrating better optical
transparency. The electro-optic coefficients of crosslinked TLD3/TLD4
was as high as pm/V, respectively, which is also one of the highest
electro-optic coefficients of cross-linked materials. The long-term
alignment stability test showed that after being left at 85 ℃ for 500
hours, the cross-linked chromophores TLD3/TLD4 can still maintain more
than 98% of the original electro-optical coefficient value, which is
higher than that of TLD1/TLD2 (93%).
The cross-linked chromophores TLD3-4 with 5FPh-TCF as the acceptor has a
higher glass transition temperature, better transparency, and leading
electro-optic coefficient, all of which are major breakthroughs in the
design of binary cross-linked electro-optic materials
Thank you very much for your considering our manuscript for potential
publication. I’m looking forward to hearing from you soon.
Best regards
Fenggang Liu
School of Chemistry and Chemical Engineering, Guangzhou University,
Guangzhou 510006, P. R. China. E-mail address:liufg6@gzhu.edu.cn