Z.-Z. Chen, Y.-H. Deng, T. Zhang et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 262 (2021) 120084
6.19. Found: C, 63.86; H, 5.37; N, 6.06. 1H NMR (500 MHz, CDCl3)
d = 10.89 (s, 1H, ÀOH), 10.35 (s, 1H, ÀOH), 9.84 (s, 1H, ÀOH),
9.42 (s, 1H, ÀCHO), 9.11 (s, 1H, ÀN = CH), 8.18 (s, 1H, ÀN = CH),
7.95 (d, J = 8.5 Hz, 1H, ÀArH), 7.78 (d, J = 8.8 Hz, 2H, ÀArH), 7.52
(t, J = 7.7 Hz, 1H, ÀArH), 7.37 (t, J = 7.5 Hz, 1H, ÀArH), 7.20 (d,
J = 9.0 Hz, 1H, ÀArH), 7.12 (s, 1H, ÀArH), 6.80 (s, 1H, ÀArH), 4.43
(t, J = 6.2 Hz, 2H, ÀCH2), 4.39 (t, J = 6.2 Hz, 2H, ÀCH2), 2.23 (m,
J = 6.2 Hz, 2H, ÀCH2) (Fig. S1). 13C NMR (126 MHz, DMSO d6)
yellow dye, was produced by Blanc chloromethylation, Duff reac-
tion and methoxy reduction. The TNS was obtained through a sim-
ple Schiff base reaction. Then the TNS part was introduced into one
side of the dialdehyde skeleton to develop a new dye probe p-TNS.
The structure of the p-TNS was characterized by 1H NMR, 13C NMR,
HRMS and IR (Fig. S1-S4).
Interestingly, the probe molecules exhibited yellow and green
solid-state fluorescence in visible and UV light (365 nm), respec-
tively. (Fig. S5). As shown in Fig. 1(a), the calculation by the Multi-
wfn program clearly showed the charge distribution of the probe
p-TNS molecules, in which electron-deficient parts are mainly con-
centrated at the carbon atoms of C@N and C@O functional groups.
This implied that the nucleophilic addition reaction may occur at
this site [22,48]. Besides, Some common chemical reactions may
also happen in the electron-rich part [49], all of which have been
marked in Fig. 1(b). Three pairs of intramolecular hydrogen bonds
were also found in the probe p-TNS, the bond lengths of which can
be observed in Fig. 1(c) and (d).
d
= 190.52, 156.82, 153.77, 149.06, 147.86, 145.00, 132.82,
131.75, 129.05, 128.53, 128.16, 126.21, 124.49, 124.20, 123.87,
118.63, 114.11, 114.05, 108.87, 71.26, 70.88, 29.13 (Fig. S2). HRMS
: m/z: calcd for C22H20N2O6: 408.06, found: 407.19 [M À H]À
(Fig. S3). IR (KBr, cmÀ1): 3410 (m), 2960 (m), 2893 (w), 2841 (w),
1674 (s), 1626 (w), 1500 (s), 1469 (s), 1343 (w), 1299 (m), 1233
(w), 1011 (s), 933 (m), 816 (s), 667 (s) (Fig. S4).
2.3. Spectra measurement
The probe p-TNS (5.0 Â 10-3 molÁdmÀ3) and all analytes
(5.0 Â 10-2 molÁdmÀ3) were prepared in DMSO and pure water
solution, respectively. During the experiment, the probe p-TNS
was mixed with different analytes in equal volumes, while ensur-
3.2. Photophysical properties
In molecular design, the naphthyl group was introduced into
one end of the dialdehyde molecular skeleton, so that the probe
may have an intramolecular charge transfer (ICT) effect. Moreover,
an excited state intramolecular proton transfer (ESIPT) characteris-
tic may be formed between adjacent aldehyde and hydroxyl
groups. Therefore, the photophysical properties of the probe mole-
cule in solution should largely depend on the solvent polarity [50–
51].
ing that the concentration of the probe was 5.0 Â 10À5 molÁdmÀ3
,
and the test system was selected in DMSO/H2O (9/1 = v/v,
pH = 7.0). Moreover, 365 nm was selected as the excitation
wavelength.
2.4. Theoretical calculations
The theoretical analysis of the probe p-TNS was performed in
the Multiwfn program [43–44]. Moreover, through the density
functional theory (DFT) method in the Gauss 09 program [45–
47], the structure, orbit, energy gap and molecular electrostatic
potential (MEP) of the probe molecule and products were
calculated.
In order to confirm our conjecture, the absorption and emission
spectra of the probe molecule were measured in various common
solvents to evaluate the influence of solvent polarity on
photophysical properties. In Fig. 2(a), the absorption spectra indi-
cated that the probe molecule has three characteristic absorption
bands in different solvents. As the solvent polarity increases from
toluene to methanol, the absorption peaks only slightly change.
On the contrary, form Fig. 2(b), the more obvious solvation behav-
ior (from 453 to 493 nm) was recorded in the emission spectrum.
The emission wavelength showed a red shift with the increase of
solvent polarity, which provides strong evidence for the possible
existence of ICT effect in the probe molecule [52]. These results
indicated that the emission properties of the dye probe p-TNS have
3. Results and discussion
3.1. Design and synthesis of the dye probe p-TNS
The synthesis process of the dye probe p-TNS is illustrated in
Scheme 1. 2.5-Dihydroxyterephthalaldehyde (p), as an orange-
Fig. 1. (a) Electron distribution in the probe molecule; (b) possible recognition sites of the initially designed probe; (c) intramolecular critical point and hydrogen bond
length; (d) simplified image of hydrogen bond.
3