Changing Ï-Interactions and Conformational Adjustments of N

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Changing #-interactions and conformational adjustments of N-(isonicotinylhydrazide)-1,8-naphthalimide by hydration and complexation affect photophysical properties Jubaraj B. Baruah, and Arup Tarai Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.7b01444 • Publication Date (Web): 13 Dec 2017 Downloaded from http://pubs.acs.org on December 14, 2017

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Crystal Growth & Design

Changing π-interactions and conformational adjustments of N-(isonicotinylhydrazide)-1,8naphthalimide by hydration and complexation affect photophysical properties

Arup Tarai, Jubaraj B. Baruah* Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati -781 039, Assam, India. Fax: +91-361-2690762; Ph. +91-361-2582311; email: [email protected] http://www.iitg.ernet.in/juba

Abstract: Non-covalent self-assemblies of different forms of a 1,8-naphthalimide derivative N(isonicotinylhydrazide)-1,8-naphthalimide adopt different conformational adjustments due to interplay of weak interactions. In such assemblies stacking interactions significantly contribute to direct the orientations of tether, which also influenced packing patterns. Effects of weak noncovalent interactions are reflected in the physicochemical properties of solvate and metal complexes of this naphthalimide derivative. Dual fluorescence emissions were observed from hydrate and silver complex of N-(isonicotinylhydrazide)-1,8-naphthalimide, which was not observed in anhydrous form of the compound. These results are compared with fluorescence emission study performed with solution of N-(isonicotinylhydrazide)-1,8-naphthalimide. Aggregation induced fluorescence emission of a solution in DMSO was caused by adding water. This emission in solution occurred at much different emission wavelength than the emission observed from the hydrated sample in solid state. It is also established that the aggregation induced fluorescence of N-(isonicotinylhydrazide)-1,8-naphthalimide caused by adding water to a solution of the compound in dimethylsulphoxide can be quenched by different nitro-phenols.

Key

words:

Naphthlalimide;

Stacking

interactions;

Conformational

adjustments;

Photoluminsence; Aggregation. Introduction: Among the weak interactions, π-interactions such as π-stacking,1-3 C-H···π interactions,4-5 NH···π,6 O-H···π,7 anion-π interactions,8-14 cation-π interactions15-16 are of prime concern in crystal engineering. Aromatic-imide derivatives are useful to study different π-stacking interactions17-19 1

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and the impact imparted by such interactions greatly affect photoluminescence properties of fluorphores in solids.20-26 The progress of aggregation induced emissions in solid have made the emission properties of solids very interesting.27-29 The conformations guided by a substituent contributing to twisted intramolecular charge transfer in aggregates have made significant progress to tune fluorescence emission in self-assembled systems.30-32 Scientists from different backgrounds are putting attention in tuning signal transductions of naphthalimide derivatives due to their easiness in handling and available literature.33 In packing pattern, stacking among naphthalimide rings changes significantly of a naphthalimide bearing ligand coordinated to metal ions from corresponding stacking of the free ligand.34-38 The л–л and C–H···O interactions arising due to naphthalenediimide unit are utilized to modulate the dynamic process in interlocked systems.39-40 Stacking patterns of naphthalimide in ionic derivatives also changes with anions.41-42 Depending on coformers in cocrystals and solvent in solvates of naphthalimides the stacking patterns vary.43-46 Dipolar nature of naphthalimide influences π-stacking, contribute to fluorescence emission in solid state.47-48 Some of the π-stacking interactions among

(a)

(b)

Figure 1: (a) Different л-stacking arrangements of naphthalimide rings and (b) supramolecular features associated with N-(isonicotinylhydrazide)-1,8-naphthalimide (HL).

naphthalimide rings are shown in Fig. 1a. We felt that introducing a pyridyl-amide group that possess an additional nitrogen atom containing ring would enhance the impact of such a study through modulation of the orientation of the amide group. A molecule such as N(isonicotinylhydrazide)-1,8-naphthalimide (HL in Fig. 1b) has such feature, it would not only 2


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provide information on л-stacking interactions but also would provide scope to study twisted intramolecular charge transfer emission path.30-32 The compound HL is comprised of a dipolar naphthalimide ring to form л-stacks, it also has a partially rotatable amide linker to connect a pyridine unit a hydrogen bond acceptor or complex formation site. Impact of orientations of the donor with respect to acceptor of such a molecule would make impact on photoluminescence. There is a definite scope to understand different photoluminescence process of cocrystals and solvates through crystal packing due to the advantage of having locked geometries in solids. The present study is directed towards studying the structure and photophysical study on anhydrous, hydrated and a silver complex of compound HL. In these forms, the carbonyl group of the amide part should orient in dissimilar manners due to changes in packing patterns by factors such as πstacks, hydrogen bonds or metal coordination. Results and discussion: Structural descriptions of anhydrous and hydrated form of HL: The anhydrous and hydrated form of the HL was obtained by crystallisation from solution in acetone or methanol containing water (~10%) respectively. Clear distinctions between these two crystalline forms, namely, hydrate and anhydrous forms were observed in respective IR spectra. A weak N-H stretching absorption at 3475 cm-1 was observed in the case of anhydrous form and for the O-H and N-H stretching of hydrate form a relatively sharp and broad stretching at 3471cm-1 was observed (Fig. 1S). Generally N-H and O-H frequency of a compound are observed in the region 3200-3500 cm-1. The carbonyl stretching of the anhydrous form of HL appear at 1720 cm-1 and 1690 cm-1, whereas in the hydrated form these stretching appear at 1718 cm-1and 1682 cm-1. The structure of the compound HL, hydrate of HL and complex of HL with silver nitrate were determined by single crystal X-ray diffraction. The unit cells of the HL as well as HL hydrate have two symmetry independent molecules. The structures of the hydrate and anhydrous forms have wide difference in the stacking patterns among the naphthalimide rings as well as hydrogen bond patterns. The packing of anhydrous form has pyridine nitrogen in two different environment, in one set nitrogen atom is involved in bifurcated hydrogen bonds comprising of C-H···N and N···H-N interactions (Fig. 2a). Nitrogen atom on another symmetry independent molecule is involved in N···π aromatic interactions (d N···π = 3.237 Ǻ) between two independent aromatic rings. In literature π-π interactions among pyridine rings are observed49 but 3



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having a direct N···π interactions are not conventional. The naphthalimide rings of two molecules stack slightly offset but in parallel manner having centroid to centroid distance 3.568

(a)

(b)

(c)

(d)

Figure 2: Hydrogen bonded self-assemblies in (a) HL and (b) HL.H2O; (c) and (d) are πstacking observed in the packing patterns of HL and HL.H2O respectively. Ǻ; a distance conducive to have definitely a π-interaction.1-3 This π-stacked geometry is further stabilised by C5-H5···O3(C=O) interactions (dd···A = 3.344 Å). But the naphthalimide rings of the hydrated form HL.H2O are stacked in different manners than the anhydrous form. Each water molecule of hydrate acts as hydrogen bond donor and acceptor to anchor three HL molecules. Such hydrogen bonds help to propagate the assembly along a-crystallographic axis as illustrated in Fig. 2b. In this hydrogen bond scheme, one hydrogen atom of water molecule is linked to oxygen atom of carbonyl of a naphthalimide; whereas other donor forms hydrogen bonds with amide oxygen atom of another molecule. The oxygen atom acts hydrogen bond acceptor to N-H 4


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bond of amide. The nitrogen atoms on pyridine rings are involved in C-H···N hydrogen bond by utilising of one C-H on the naphthalimide ring. Such weak interactions result in one-dimensional chain-like arrangement along a-crystallographic axis. Hydrogen bonded assembly has parallel stacks among naphthalimide in head to tail fashion. There are two types different separating distances between the parallel rings are observed which are 3.720 Ǻ and 4.055 Ǻ (Fig. 2d), whereas only single centroid-centroid distance among π-stacked rings was observed in anhydrous form of HL (Fig. 2c). Thus, the major differences in hydrogen bonds present in the hydrate and anhydrous form are result of participation of nitrogen atom of pyridine ring in forming hydrogen bonds and due to the stacking arrangements among the naphthalimide rings. The prominent hydrogen bond parameters are listed in Table 1.

Table 1: Hydrogen bond parameters of HL and HL.H2O D-H…A

dD-H (Å)

dH…A (Å)

dD…A (Å)

∠D-H…A (o)

HL

N(2)-H(2)…N(6) [x, y, z] N(5)-H(5A)…O(1) [-1+x,y,z]

0.86(4) 0.86(4)

2.11(7) 2.02(5)

2.847(3) 2.833(2)

143(4) 157(3)

HL.H2O

N(2)-H(2)…O(8) [x, y, z] N(5)-H(5A)…O(7) [1-x,-y,1-z] O(7)-H(7A)…O(6) [x, y, z] O(8)-H(8A)…O(2) [1-x,1-y,-z]

0.86(4) 0.86(5) 0.854(8) 0.86(7)

1.98(3) 2.05(6) 1.92(3) 2.04(7)

2.782(7) 2.751(7) 2.741(7) 2.872(7)

154(3) 138(5) 162(7) 165(6)

Compound

Analysis of fingerprint plots obtained from Hirsfeld analyses50-51 on the extent of weak interactions in the anhydrous and hydrate forms have revealed that the percentages of O-H interactions in these forms, and they are found to be closely comparable. The hydrated form has about three percentage higher N-H interactions over the anhydrous form (Table 1S). This is due to participation of pyridine nitrogen in hydrogen bonds in the hydrated form, which is not case in anhydrous form. Significant difference occurs in the C-H interactions, the anhydrous form has 29.7 % such interactions (Fig. 3), whereas the hydrated form has 18.0 %, this is attributed to the hydration; which segregated the molecules to make lesser C-H interactions.

5



(a)

(b)

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(c)

(d)

Figure 3: Hirshfeld surface of (a) HL and (b) HL.H2O. Fingerprint plots for (c) HL and (d) HL.H2O with C…H interactions highlighted in colour.

Thermal studies of anhydrous and hydrated form of HL: Thermogravimetric analysis of hydrated form of HL shows weight loss for water molecules at 103°C‒141°C (Fig. 4a) from HL.H2O, whereas no such weight loss was found in the case of anhydrous HL. Loss of water molecule from hydrated sample on heating was confirmed by FTIR studies of the hydrated sample annealed at this temperature. The IR spectrum of such sample is identical to the IR spectra of anhydrous form of HL. Differential scanning calorimetry (DSC) is conventional tool to understand phase transitions in solid organic samples.52 The DSC of anhydrous form shows only one endothermic peak due to melting at 293°C, whereas hydrated form HL.H2O shows two different endothermic peaks one for water evaporation and another for melting (i of Fig. 4b and 4c). Upon cooling the melted sample showed two closely spaced exothermic peaks at temperatures 181°C and 185°C (i of Fig. 4b). Our attempt to get crystals from melt crystallisation was not successful. The powder XRD patterns of the solid from melt have similar patterns but with broad peaks suggest that both amorphous and crystalline forms were formed during solidification from melt. Optical microscopic study was not attempted due to very close temperature difference of the two exothermic peaks observed during cooling. Hydrate crystal shows identical melting point as that of the anhydrous form, possibly due to its transformation to anhydrous form. However, on cooling it shows closely spaced exothermic process at 192 °C and 194 °C (i of Fig. 4c). The second cycle of heating showed that in both the cases they melt at 291°C, which is due to anhydrous form but depression of melting point is associated with presence of small amount of amorphous phase. 6


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(a)

(b)

(d)

(c)

(e)

Figure 4: DSC plots of (a) HL and (b) HL.H2O with (i) 1st cycle and (ii) 2nd cycle heating. FESEM images of HL from (c) DMSO and (d) 1:9 DMSO-H2O solvents mixture. The recrystallization process during cooling in second cycle occurs at two different temperatures in each case. For anhydrous form it occurs at 185 °C and 170 °C (ii of Fig. 4b) whereas for hydrated form these are at 181 °C and 160 °C (ii of Fig. 4c). These are indicative of the fact that the anhydrous form is formed in each case with another uncharacterised amorphous phase. In fact this is true as the anhydrous form or the anhydrous material obtained by dehydration of hydrated form (obtained by heating at 150°C) does not absorb water molecules from moisture in air. However, these anhydrous crystals re-dissolved in aqueous methanol, easily crystallised in hydrated form. We examined the morphologies of HL obtained from a solution in DMSO solvent another sample that was prepared from a solution of HL in mixed solvent DMSO and water in 1: 9 v/v ratio by adopting drop-cast method. The morphology of the sample obtained from DMSO solution differs from sample obtained from a solution of mixed solvent of DMSO and water in 1: 7



9 v/v ratio. Fibrous structures were observed in the former case (Fig. 4d) and rod-like crystals were obtained from mixed solvent (Fig. 4e). These results indicated that the sizes and the morphologies of the crystals were dependent on the solvents and by changing solvent fibrous to crystalline structures can be prepared. It may be mentioned that we could not observed good quality single crystals for recording single crystal diffraction by crystallisation of HL from its solution in DMSO and the possible reason could be due to agglomeration guided by DMSO as seen in the morphology study.

Figure 5: The stacking arrangements among naphthalimides assisted by weak interaction in Ag(HL)2.NO3. The silver nitrate complex with HL is obtained as hydrate and the complex has two HL ligands coordinating to a silver ion to provide a two-coordinated environment around the metal ion linear geometry. In fact the lattice water molecules forms C-H···O bonds with C-H at ortho position of pyridine rings from two independent ligands as illustrated in Fig. 5 blocks the approach of a third ligand. This is a reason we get 2-coordinated complex rather than four coordinated silver complex of naphthalimide derivatives reported earlier.53 There are many examples of silver complexes of pyridine derivatives where silver-silver interactions are prominent;54 we do not observe such interactions. The nitro group of the complex is involved in hydrogen bond formation with water molecule. In general hydrated nitrate anions generate theoretical interest55 and their stable geometries are essential, in fact we have been able to stabilize NO3-(H2O) by interaction through the interaction of N-H of amide group as shown in Fig. 5. The hydrated nitrate ion has the packing pattern indicates that there are stacking among the naphthalimide rings, but the centroid to centroid distance between such stacks is 4.246 Å. This distance 8


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suggests that the π-π interactions between the naphthalimide rings are very weak, yet this stacking arrangement is essential to provide the stable structure. The oxygen atom of the carbonyl atom on amide unit attached to ligands participating in stacking as pair (Fig. 5), form hydrogen bond with the N-H bond of the amide on the other ligand and the corresponding d(D…A) is 2.853 Å. The details of hydrogen bond parameters of [Ag(HL)2]NO3.H2O complex are listed in Table 2S. The complex shows broad strong peak at 3484 cm-1 due to O-H of water and N-H of ligand. It shows sharp carbonyl stretching at 1723 cm-1 and 1689 cm-1 and the nitrate stretching appears as sharp band 1383 cm-1. Photoluminescence properties: A close examination of the overlaid diagram of the hydrate and anhydrous form shows that the orientation of the amide bearing unit with respect to the naphthalimide ring differs and this is reflected in the torsion angle listed in the Table 2. The overlay diagram of these two forms clearly shows that the orientation of the carbonyl group of the amide makes a large difference (Fig. 6a). Orientation of rings affecting fluorescence in dipyridyl derivatives are reported in literature.56 Table 2: Torsion angles of anhydrous, hydrate and silver salt of HL. HL.H2O

[Ag(HL)2]NO3.H2O

C1-N1-N2-C13/ C19-N4-N5-C31

-70.29/ -80.63

-83.42/ 83.86

-83.38/ 76.05

N1-N2-C13-O3/ N4-N5-C31-O6 N1-N2-C13-C14/ N4-N5-C31-C32

-6.41/ 1.53 172.76/ -179.64

4.29/ 8.20 -173.53/ -172.41

2.66/ -0.07 -174.36/ -178.68

Torsion angle (°)

HL

We observed visual distinction between the hydrate and anhydrous forms and distinct differences in emission are observed upon exposure of these samples to a 365 nm UV-lamp (Fig 6b). The solid sample of the hydrate has absorption at 381 nm, whereas hydrate has at 391 nm (Fig. 2S and Table 3). This distinction is not very clear but the emission properties of the two forms are wide apart. In the solid state fluorescence spectra of the hydrate, it showed dual emissions at 416 nm and 520 nm upon excitation at 365 nm. Whereas, a solid sample of the anhydrous form under similar excitation showed emission at 456 nm. In our earlier study it was shown that substituents at a remote site of thiazole derivatives with amide linkage modulate ICT, helping to distinguish metal ions.57 Naphthalimide derivatives are used to encapsulate guest causing change in 9



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fluorescence,58-60 but in present case we clearly depict an example to show the differences in fluorescence caused by hydration. Although there are examples in which the reversible dehydration and rehydration affecting fluorescence are well demonstrated in metal-organic frameworks or non-covalent assemblies,61-63 the present system is clear to depict the packing changes. In the present case no porous desolvate was formed making the emission changes irreversible after dehydration.

Table 3: Characteristic absorbance, fluorescence emission and fluorescence life-time of HL, HL.H2O and [Ag(HL)2]NO3.H2O in solid state. Compound HL

λab (nm) 381

λex (nm) 330

λem (nm) 456

HL.H2O

391

330

416 and

Quantum yields ΦF 0.49 0.88

520

Life-time (fraction) (ns, %) 30.55 (95.16)

Fitness (χ2) 1.267

Emission at 416 nm:

1.060

Bi-exponential 0.17 (24.70) and 12.63 (75.30) Emission at 520 nm:

1.062

16.83 (100 %) [Ag(HL)2]NO3.H2O

379

330

445 and

0.82

553

Emission at 445 nm: Bi-exponential 0.19 (58.64) and

1.288

5.14 (41.36) Emission at 550 nm:

1.080

Bi-exponential 0.45 (12.81) and 9.90 (87.18)

Silver complex is in hydrate form, it showed dual emissions at 445 nm and 553 nm (Fig. 3S). The shifts in emissions towards higher wavelength in this case are due to silver ion having fully filled d-orbitals. The excitation spectra were checked by exciting solid samples of HL, HL.H2O and [Ag(HL)2]NO3.H2O at respective emission wavelength. The observed excitation spectra are shown in supporting Fig. 17S. In each case broad excitation spectra that were invariant each with excitation maxima at 364 nm was observed. Thus, this invariance together with the observed large Stoke’s shift in each example supports that the energy of ground state in any of the case does change significantly. Whereas the contribution from the respective excited state played the major change in the change in emission wavelength and mode of emission. Furthermore, the fluorescence decay profiles of the solid samples were recorded and the life-times are listed in Table 3. HL has about 95 % of the molecules adopting single emission path with a relatively longer life-time 30.55 ns suggesting exciplex emission. But the emission decay path of the 10


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hydrated sample in DMSO has bi-exponential paths for the shorter wavelength and single expontial path for longer wavelength emission. In the case of silver complexes both longer and shorter wavelength emission follows bi-exponential decay paths.

(a)

(b)

(c)

Figure 6: (a) Overlay diagrams of structures anhydrous (red) and hydrated (black) forms of HL. (b) Appearances of crystals of HL and HL.H2O under normal light and UV-lamp (365 nm). (c) Fluorescence emissions spectra (λex = 330 nm in each case) of solid sample of (i) HL and (ii) HL.H2O. An orientation of HL that enables higher amounts of overlap of the LUMO with the orbitals of the oxygen atom of carbonyl will inhibit the excitation process for intramolecular charge transfer (ICT). To check such possibility, torsion angles of the amide and imide units in the three structures are analysed (Table 2). It is clear that the carbonyls of amides in anhydrous form are almost perpendicular direction as that of the naphthalimide ring, which is different in hydrate. This is reflected in the C1-N1-N2-C13 angle which is -83.42° in hydrate, and is -70.29° in the case of anhydrous form. On the other hand, in the silver complex it is -83.38° (Table 2). The rest torsion angles are comparable; but differences of C1-N1-N2-C13 torsion angles make large impact on the solid state fluorescence emissions. Analysis of molecular orbitals of the hydrate and anhydrous forms shows that +ve and –ve lobe of π-type orbital of the LUMO lies across the imide containing ring. These π-orbitals may have constructive overlap with the electron of the lone pair (sp2) hybrid orbital of oxygen atoms of carbonyl in case of non-perpendicular arrangement (Fig. 7b and 7d), whereas zero overlap when carbonyl group is perpendicular to the 11



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ring. Thus, at excited state electron transfer from oxygen to LUMO is inhibited in anhydrous form; accordingly the emission at shorter wavelength is not observed. Whereas, in the case of hydrate and silver salt such interactions create zero overlap, hence the emission at shorter wavelength is observed. The emission paths involved in TICT30-32 is shown in Fig. 7e.

(a)

(b)

(c)

(d)

(e) Figure 7: (a) HOMO, (b) LUMO of HL and (c) HOMO, (d) LUMO of HL.H2O, (e) Emission paths involving TICT to show dual fluorescence. To provide support to our observations and also to find utility, we explored emission properties of HL in solution. In solution the geometry of the carbonyl of amides are guided by solute12


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solvent interactions and in such situation normal fluorescence emissions characteristic of naphthalimide units are observed. The compound HL when dissolved in DMSO showed fluorescent emission at 383 nm. This emission is due to ICT transition but partially quenched by lone pair of on the carbonyl of amide. Addition of water to this solution causes increase in this emission and it increases gradually with water content and reaches a maximum with slight shift in position of the wavelength from 383 nm to 394 nm (Fig 8a). Thus, there are changes in intensity of emission as well as small shift in emission position. The intensity increase is due to the change in orientation of the carbonyl of amide and shift in emission wavelength is due to participation of water in aggregation formation. DLS study has shown that the compound forms aggregate in DMSO solution with 174.0 nm dimension, whereas the aggregate formed in 1:9 DMSO-H2O solvent mixture is 363.3 nm (Fig. 8b and 8c). Thus, it is an aggregation induced emission owing to the changes in the type of self-assemblies. This fact is supported by similar changes in emission of a solution of [Ag(HL)2]NO3.H2O complex in DMSO to which water was added in different aliquots (Fig. 4S). A mass spectrum of the solution shows that silver complex remains intact in solution. DLS study on solution of [Ag(HL)2]NO3.H2O in DMSO showed aggregation with average particle size 97.10 nm and whereas the aggregates in 1:9 DMSO-H2O solvent mixture is 216.5 nm (Fig. 4S). In solution mass spectrometry silver complex shows mass for m+ + 1 at 742.9943. Despite of difference in particle sizes and nature of these compounds namely one as ligand other as silver complex being different, yet showing same trend in emission at identical wavelength helped us to safely conclude that contribution of the carbonyl interacting differently with the π-cloud enhances or reduces emission intensity in solutions. Similar interpretation may be also extrapolated from the observation of changes in emission of different solid samples.

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(a)

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(b)

(c)

(d)

Figure 8: (a) Fluorescence emission enhancement of HL with different fraction of water in DMSO; DLS-based particle size analysis of HL from (b) DMSO and (c) 1:9 DMSO-H2O solvent mixture; (d) Relative quenching of fluorescence emission of HL (10-4M) in 9:1 H2O-DMSO solvent by different nitro-phenols.

The fluorescence life-time of emission of compound HL dissolved in DMSO decays through biexponential paths of which about ~75 % have life-time 0.17 ns whereas ~25 % have 2.38 ns. Whereas, in 1: 9 DMSO-H2O mixed solvent the emission follows single path with life-time 0.09 ns. This establishes the fact that upon increase in water content the path involving relatively larger life-time gets inhibited and single path is followed due to aggregation caused by water. Based on this point we have extended the utility of the emission observed with 1:9 DMSO-H2O mixed solvent by studying the effect of quenching of the fluorescence emission by different 14


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nitrophenols. It is found that 4-nitrophenol, 2,4-dinitrophenol and 2,4,6-trinitrophenol causes quenching of fluorescence. But the relative quenching varied with numbers of nitro-groups on the ring. To a solution of HL in 1: 9 DMSO-H2O mixed solvent when picric acid is added, the emission decay follows single exponential path similar to the original solution but life-time is 0.07 ns which is shorter than the original solution of HL in 1: 9 DMSO-H2O mixed solvent. Such decrease causes quenching of emission. The relative differences in fluorescence emission quenching one can differentiate the nitro-phenols through such a study (Fig. 8d). The aggregation induced emission of certain naphthalimide derivatives have been explored,59-60 on the other hand the hydration of metal-organic frameworks and self-assemblies of inorganic complexes or organic compounds are commonly used for detection of water in solvent by fluorescence modulation61-63 but our present findings clearly depict that in the case of an ICT driven fluorophore such as HL the native fluorescence state matters that can be fine-tuned to switch on and off by changing the parameters contributing to the orientation of the group contributing to stabilise such a state controlling interactions among the chromophore or modifying electron delocalisation. On the other hand, the fluorescence sensing of nitro compounds by fluorescence ON and OFF process shown by receptors such as quantum dots and inorganic, organic receptors are widely studied,64-70 present example also adds one to such possibility with a difference that the a aggregation induced state can be first generated through water and further exploited to quench emission from such state by adding aromatic nitrophenolic compounds. Conclusions: In this study we have established the stacking patterns affecting the conformation of the N(isonicotinylhydrazide)-1,8-naphthalimide

that

influences

significantly

the

fluorescence

emission. The orientation of the carbonyl group of amide with respect to naphthalimide ring decided the faith of twisted intramolecular charge transfer emission in the hydrate, silver complex and anhydrous form of the compound. Aggregation induced fluorescence emission observed in solution is much different from the fluorescence emission observed from the solid samples. The aggregation induced fluorescence emission of HL is tuned by nitro-phenols and a possibility to detect them by a simple analyte is shown. Experimental Section: 15



Synthesis and characterisation: Synthesis of N-(isonicotinylhydrazide)-1,8-naphthalimide (HL): Compound HL was prepared by reacting isonicotinylhydrazide (0.274 g, 2mmol) and 1,8-naphthalicanhydride (0.40 g, 2 mmol) dissolved in 20 ml DMF. The solution was kept at 100°C overnight with constant stirring. The reaction mixture was cooled and poured into a beaker containing ice cold water (100 ml). A colorless precipitate obtained was filtered and dried in air. The dry product was dissolved in acetone and slow evaporation of the solution under open atmosphere resulted in crystals of anhydrous HL. Isolated yield: 77 %. 1H NMR (600 MHz, DMSO-d6): 11.74 (s, 1H), 8.88 (s, 2H), 8.60 (t, J = 6 Hz, 4H), 7.97 (t, J = 12 Hz, 2H), 7.93 (d, J = 6 Hz, 2H). 13C NMR (150 MHz, Acetone-d6): 162.6, 161.5, 151.7, 136.3, 136.0, 133.6, 132.5, 128.4, 128.2, 122.3, 120.2. IR (KBr, cm-1): 3318 (s), 3050 (w), 2813 (w), 1720 (s), 1690 (s), 1672 (w), 1586 (s), 1527 (s), 1488 (w), 1434 (m), 1408 (s), 1375 (m), 1292 (s), 1236 (s), 1181 (s), 1157 (w), 1124 (s), 1064 (s), 1043 (m), 1025 (m), 1004 (m), 928 (s), 899 (s), 884 (s), 797 (m), 775 (s), 751 (s), 733 (m), 701 (s), 635 (s). ESI mass: calcd 318.0879 [M + H+]; found 318.0880 [M + H+]. Hydrate of HL (HL.H2O): Hydrated crystal of HL was obtained on slow evaporation from methanol solution of HL at room temperature. Isolated yield: 73 %. IR (KBr, cm-1): 3471 (br, w), 2982 (w), 1718 (s), 1682 (s), 1586 (s), 1553 (s), 1512 (w), 1433 (m), 1408 (s), 1378 (m), 1309 (s), 1234 (s), 1183 (s), 1150 (m), 1131 (m), 1067 (m), 1027 (m), 997 (s), 935 (s), 894 (s), 849 (s), 796 (w), 775 (s), 755 (s), 734 (m), 703 (s), 638 (s). Synthesis of silver complex [Ag(HL)2]NO3.H2O: Silver complex of HL was synthesized by reacting HL (0.317 g, 1 mmol) with silver nitrate (0.084 g, 0.5 mmol) in DMF-acetone solvent mixture at room temperature. The reaction mixture was stirred overnight, resultant solution was kept undisturbed. After 15 days colourless crystals of [Ag(HL)2]NO3.H2O were formed. Isolated yield: 63 %. 1H NMR (600 MHz, DMSO-d6): 11.75 (s, 1H), 8.88 (d, J = 6 Hz, 2H), 8.61 (d, J = 6 Hz, 2H), 8.59 (d, J = 6 Hz, 2H), 7.97 (t, J = 6 Hz, 2H), 7.93 (d, J = 6 Hz, 2H). IR (KBr, cm-1): 3484 (br, s), 1723 (s), 1689 (s), 1586 (s), 1554 (m), 1523 (m), 1494 (w), 1435 (m), 1383 (vs), 1300 (s), 1234 (s), 1181 (s), 1155 (m), 1131 (w), 1067 (m), 1044 (s), 1026 (w), 1001 (s), 927 (s), 889 (s), 845 (s), 775 (s), 757 (w), 731 (w), 699 (m), 637 (s). HRMS observed 742.9974, calcd (m+ + 1) = 742.0730.

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Crystallographic parameters of the HL, HL.H2O and [Ag(HL)2]NO3.H2O are listed in table 4. Table 4: Crystallographic parameters of HL, HL.H2O and silver complex: HL C18H11N3O3 1578654 317.30

HL.H2O C18H13N3O4 1578655 335.31

8.5702(3) 9.4285(3) 20.5972(6) 79.271(2) 81.421(2) 63.104(2) 1454.35(8) 1.449 0.102 656 5069 3521 25.04

7.3514(12) 14.511(2) 15.177(3) 102.596(12) 90.404(13) 90.108(15) 1580.0(5) 1.410 0.102 696 5489 2751 25.04

[Ag(HL)2]NO3.H2O C36H24AgN7O10 1578656 822.49 Pbca 13.270(2) 17.250(3) 28.462(5) 90.00 90.00 90.00 6515.2(19) 1.677 0.694 3328 5887 3217 25.24

Ranges (h, k, l)

−9 ≤ h ≤ 10 −11 ≤ k ≤ 11 −22 ≤ l ≤ 24

−8 ≤ h ≤ 8 −16 ≤ k ≤ 16 −18 ≤ l ≤ 16

−15 ≤ h ≤ 14 −20 ≤ k ≤ 20 −26 ≤ l ≤ 34

Complete to 2θ (%) Data/restraints/parameters GooF (F2) R indices [I > 2σ(I)] wR2 [I > 2σ(I)] R indices (all data) wR2 (all data)

98.30 5069/0/433 1.039 0.0459 0.1335 0.0649 0.1549

98.10 5489/8/ 467 1.034 0.0919 0.1925 0.1403 0.2090

100.00 5887/0/490 1.025 0.0552 0.1490 0.1100 0.1750

Formula CCDC no. Mol. wt. Space group a/Å b/Å c/Å α/° β/° γ/° V/Å3 Density/gcm−3 Abs. coeff./mm−1 F(000) Total no. of reflections Reflections, I > 2σ(I) Max. θ/°

Supporting Information: Crystallographic information files are deposited to Cambridge Crystallographic Database and have the CCDC numbers 1578654-1578656. FT-IR, UV-visible, DLS, mass spectra, 1H NMR, powder XRD patterns, fluorescence spectra, emission spectra, fluorescence decay profiles, table for hydrogen bond parameters and energy values from DFT are available. This material is available free of charge via internet at http://pubs.acs.org. Acknowledgements: Authors thank Ministry of Human Resource and Development, India for providing support through Grant No. F. No. 5-1/2014-TS.VII.

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For Table of Contents Use Only Changing π-interactions and conformational adjustments of N-(isonicotinylhydrazide)-1,8naphthalimide by hydration and complexation affect photophysical properties

Arup Tarai and Jubaraj B. Baruah

Synopsis Conformational adjustments guided by stacking interactions in anhydrous, hydrated and silver complex of N-(isonicotinylhydrazide)-1,8-naphthalimide are studied. Dual fluorescence emission observed from solid sample of hydrated form of N-(isonicotinylhydrazide)-1,8-naphthalimide as well as of the silver complex are due to twisted intramolecular charge transfer transitions.

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Changing Ï-Interactions and Conformational Adjustments of N

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