2020 Inorg. Chem. 2010, 49, 2020–2022
DOI: 10.1021/ic9022008
Silver-Guided Excimer Emission in an Adenine-Pyrene Conjugate: Fluorescence
Lifetime and Crystal Studies
Mrituanjay D. Pandey, Ashutosh Kumar Mishra, Vadapalli Chandrasekhar,* and Sandeep Verma*
Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur 208016, India
Received November 6, 2009
This Communication describes a novel adenine-pyrene conjugate
(1) and its solid-state structure with silver and copper ions. Single-
crystal studies of metal complexes of 1 offer insight into molecular
interactions and provide a basis to rationalize possible interactions
in the solution state, leading to excimer formation. The robust
nature of this interaction was further confirmed by deposition of the
silver complex on a graphite surface, which exhibited a remarkable
resemblance to its solid-state structure. The structural basis of
selective excimer formation in the presence of Agþ ions presents a
viable approach for ratiometric detection of these ions.
quantities of silver ions is relevant to the environment and
human health. Techniques such as atomic absorption spec-
troscopy, inductively coupled plasma mass spectroscopy, and
potentiometry have been employed for silver ion detection.3
Recentreports have describedfluorescence-basedratiometric
measurement approaches to achieve better selectivity over
conventional techniques.4
Herein, we report the synthesis and structural characteri-
zation of a novel adenine-pyrene conjugate, selective sensing
of silver ions via excimer formation, and crystallographic
investigations explaining the specific detection of silver ion
over copper, another coinage metal.
Our group has dealt with silver-adenine coordination,
leading to the formation of interesting and diverse supramo-
lecular architectures.5 The facile formation of silver-adenine
complexes and their luminescent properties led us to design a
modified purine nucleobase that can not only coordinate
with silver ions but also exhibit augmented luminescence due
to an attached pyrene pendant group.
With this intention, we prepared a pyrene-based adenine
analogue, 9-[2-[(pyren-1-ylmethyl)amino]ethyl]-9H-purin-6-
amine (1; Scheme 1), and investigated its fluorescence beha-
vior in the presence of various metal ions. Screening of 1, in
the presence of metal perchlorates, revealed a high selectivity
for silver over other metal ions (Figure 1a). As shown in
Figure1a, the I470/I375 ratio for silver was very high compared
to other metal ions, with the lowest being that for the copper
ions.
The use of silver in the photographic, imaging, and
electronics industries inadvertently results in increased silver
bioaccumulation, leading to enhanced exposure and adverse
biological effects and toxicity in aquatic and terrestrial
organisms.1 Silver ions are known to interfere with biochemi-
cal processes by enzyme/protein inactivation and ionoregu-
latory imbalance.2 Therefore, the design and development of
sensitive and selective methods for the determination of trace
*To whom correspondence should be addressed. E-mail: vc@iitk.ac.in
(V.C.), sverma@iitk.ac.in (S.V.).
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The emission spectra of 1, when excited at 326 nm, show
vibronic bands with peaks at around 375 and 397 nm, which
could be attributed to pyrene emission. A significant
decrease in vibronic emission was observed with simulta-
neous enhancement at 470 nm, when 1 was titrated with
silver perchlorate because of the formation of a pyrene
excimer (Figure 1b). Fluorescence lifetime measurements
monitored at the excimer emission band, i.e., at 470 nm,
exhibit longer decay times for the silver complex 2 (16.92 ns)
compared to 1 alone (3.93 ns). This observation may be
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(b) Purohit, C. S.; Mishra, A. K.; Verma, S. Inorg. Chem. 2007, 46, 8493.
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Published on Web 01/29/2010
2010 American Chemical Society