Please do not adjust margins
ChemComm
Page 4 of 4
COMMUNICATION
Journal Name
decay profile of the final blue emitting solution of PQCz-T
obtained after the cooling-heating-cooling cycle compared to a
single lifetime of the pristine orange fluorescent solution
suggest the presence of multiple emissive species (Fig. S23,
Table S11). The temperature-dependent fluorescence of D-A
molecules with distinct charge separation is often attributed to
thermally activated delayed fluorescence (TADF).1c,20 However,
a continuous increase of the fluorescence intensity with
temperature and reversibility over the full heating-cooling cycle
is expected from an ideal TADF emitter,20,21 which is not the
case with PQCz-T. Emission studies in THF and hexane mixture
and high viscous solution of PQCz-T ascertain the temperature-
responsive tunable emission in THF is not solely due to the
variation of solvent polarity with temperature (Fig. S24-S26).
The 1H NMR spectra of PQCz-T in THF-d8 were examined to
ascertain any structural change during the heating-cooling
cycle. Even though the 1H NMR spectra at different temperature
remain similar (Fig. S27); a closer inspection of the aromatic
region reveal a slight upfield shift of the protons with the
increase in temperature (Fig. S28). Interestingly, the aromatic
protons are much more resolved after the heating-cooling
cycles suggesting certain structural change similar to that
observed by Fu and coworkers in a phenazine-based system.22 It
is likely that the pyridine moiety in PQ (acceptor) becomes
nonplanar with respect to the phenanthrene unit, partially
disrupting the ICT and causing predominantly the blue emission
from the LE state with the increase of temperature (Fig. S29).
Amidst different possible mechanisms,14 it is still challenging to
pinpoint the complete molecular level picture ascribing the
unique and diverse fluorescence behaviour of PQCz-T (Fig. S31,
S32). The present communication lays the foundation towards
the future exploration of rich photophysical attributes of PQ-
based molecular probes.
Notes and references
1
2
(a) E. Lippert, W. Lüder and H. Boos, inDAOdIv:a10n.c10e3s9i/nCM7CoCl0e9c2u6la1Jr
Spectroscopy, Pergamon, 1962, DOI: 10.1016/B978-1-4832-
1332-3.50070-6, pp. 443; (b) G. Zhou, M. Baumgarten and K.
Mullen, J. Am. Chem. Soc., 2008, 130, 12477; (c) H. Uoyama,
K. Goushi, K. Shizu, H. Nomura and C. Adachi, Nature, 2012,
492, 234; (d) K. Kawasumi, T. Wu, T. Zhu, H. S. Chae, T. Van
Voorhis, M. A. Baldo and T. M. Swager, J. Am. Chem. Soc.,
2015, 137, 11908.
(a) Z. R. Grabowski, K. Rotkiewicz and W. Rettig, Chem. Rev.,
2003, 103, 3899; (b) A. L. Kanibolotsky, J. C. Forgie, G. J.
McEntee, M. M. A. Talpur, P. J. Skabara, T. D. J. Westgate, J. J.
W. McDouall, M. Auinger, S. J. Coles and M. B. Hursthouse,
Chem. Eur. J. 2009, 15, 11581; (c) S. P. Wang, X. J. Yan, Z.
Cheng, H. Y. Zhang, Y. Liu and Y. Wang, Angew. Chem. Int. Ed.,
2015, 54, 13068.
3
4
(a) L. A. Estrada and D. C. Neckers, Org. Lett. 2011, 13, 3304;
(b) G. Haberhauer, Chem. Eur. J., 2017, 23, 9288.
(a) T. Suhina, S. Amirjalayer, B. Mennucci, S. Woutersen, M.
Hilbers, D. Bonn and A. M. Brouwer, J. Phys. Chem. Lett., 2016,
7
, 4285; (b) H. Naito, K. Nishino, Y. Morisaki, K. Tanaka and Y.
Chujo, Angew. Chem. Int. Ed., 2017, 56, 254.
5
(a) P. Mahato, S. Saha and A. Das, J. Phys. Chem. C 2012, 116,
17448; (b) S. Sasaki, G. P. C. Drummen and G. Konishi, J.
Mater. Chem. C, 2016, 4, 2731.
6
7
J. R. Lakowicz, Principles of fluorescence spectroscopy,
Springer, New York, 2006.
(a) T. Inouchi, T. Nakashima and T. Kawai, Asian J. Org. Chem.,
2013, 2, 230; (b) S. Achelle, J. Rodríguez-López, C. Katan and
F. Robin-le Guen, J. Phys. Chem. C, 2016, 120, 26986.
(a) M. A. Haidekker, T. P. Brady, D. Lichlyter and E. A.
Theodorakis, J. Am. Chem. Soc., 2006, 128, 398; (b) M. K.
Kuimova, S. W. Botchway, A. W. Parker, M. Balaz, H. A. Collins,
H. L. Anderson, K. Suhling and P. R. Ogilby, Nat. Chem., 2009,
8
1
, 69; (c) X. D. Wang, O. S. Wolfbeis and R. J. Meier, Chem. Soc.
Rev., 2013, 42, 7834.
9
Y. X. Guo, S. Z. Gu, X. Feng, J. N. Wang, H. W. Li, T. Y. Han, Y. P.
Dong, X. Jiang, T. D. James and B. Wang, Chem. Sci., 2014, 5,
4388;
In conclusion, we fabricated a new class of T and V-shaped
D-A-D type molecules employing pyridoquinoxaline as acceptor
and carbazole as donor units. The subtle variation of the
molecular shape and ICT characteristics were found to be
responsible for the polarity-dependent tunable emission across
the visible region in PQCz-T and PQCz-V. PQCz-T exhibits
environment-sensitive fluorescence with large Stokes shift,
10 B. Sk, P. K. Thakre, R. S. Tomar and A. Patra, Chem. Asian J.,
2017, 12, 2501.
11 E. Jo, J. B. Park, W. H. Lee, J. H. Kim, I. H. Jung, D. H. Hwang
and I. N. Kang, J. Polym. Sci. Pol. Chem., 2016, 54, 2804.
12 B. Wex and B. R. Kaafarani, J. Mater. Chem. C, 2017, 5, 8622.
13 W. J. Li, D. D. Liu, F. Z. Shen, D. G. Ma, Z. M. Wang, T. Feng, Y.
X. Xu, B. Yang and Y. G. Ma, Adv. Funct. Mater., 2012, 22, 2797.
14 M. Segado, I. Gomez and M. Reguero, Phys. Chem. Chem.
Phys., 2016, 18, 6861.
strong red emission in the solid state and
a drastic
15 B. Sk and A. Patra, CrystEngComm, 2016, 18, 4290.
16 S. Sasaki, S. Suzuki, W. M. C. Sameera, K. Igawa, K. Morokuma
and G. Konishi, J. Am. Chem. Soc., 2016, 138, 8194.
enhancement of fluorescence with the increase of viscosity of
the medium. A dramatic change of temperature-induced
fluorescence color in PQCz-T led to tunable emission covering
the entire visible region including a single-component near
white-light emission. Such diverse optical properties exhibited
by PQCz-T is rarely observed in a single molecular platform
(Table S12). The current study reveals a design strategy opening
up new avenues for the development of multifunctional
materials based on pyridoquinoxaline promising for
optoelectronics, sensing and imaging in biological medium.
Financial support from BRNS, DAE (no. 37(2)/14/06/2016-
BRNS/37020) and infrastructural support from IISERB are
gratefully acknowledged. BH and SK thank IISERB for fellowship.
We thank Dr. J. A. Mondal at BARC for fruitful discussion.
“There are no conflicts of interest to declare”
17 (a) S. C. Lee, J. Heo, J. W. Ryu, C. L. Lee, S. Kim, J. S. Tae, B. O.
Rhee, S. W. Kim and O. P. Kwon, Chem. Commun., 2016, 52
13695; (b) M. K. Kuimova, Phys. Chem. Chem. Phys., 2012, 14
12671.
,
,
18 (a) W. Rettig and E. A. Chandross, J. Am. Chem. Soc., 1985,
107, 5617; (b) J. Feng, K. J. Tian, D. H. Hu, S. Q. Wang, S. Y. Li,
Y. Zeng, Y. Li and G. Q. Yang, Angew. Chem. Int. Ed., 2011, 50
8072.
,
19 C. Cao, X. Liu, Q. Qiao, M. Zhao, W. Yin, D. Mao, H. Zhang and
Z. Xu, Chem. Commun., 2014, 50, 15811.
20 S. Y. Li, Y. J. Hui, Z. B. Sun and C. H. Zhao, Chem. Commun.,
2017, 53, 3446.
21 J. C. Fister, D. Rank and J. M. Harris, Anal. Chem., 1995, 67,
4269.
22 J. W. Chen, Y. S. Wu, X. D. Wang, Z. Y. Yu, H. Tian, J. N. Yao and
H. B. Fu, Phys. Chem. Chem. Phys., 2015, 17, 27658.
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins