Applicability of Reddish Orange Light Emitting Samarium (III) Complexes For Biomedical and Multifunctional Optoelectronic Devices

Six crimson samarium (III) complexes based on β-ketone carboxylic acid and ancillary ligands were synthesized by adopting grinding technique. All synthesized complexes were investigated via employing elemental analysis, infrared, UV-Vis, NMR, TG/DTG and photoluminescence studies. Optical properties of these photostimulated samarium (III) complexes exhibit reddish-orange luminescence due to 4 G 5/2 → 6 H 7/2 transition at 606 nm of samarium (III) ions. Further, energy band gap, color purity, CIE color coordinates, CCT and quantum yield of all complexes were determined accurately. Replacement of water molecules by ancillary ligands enriched the complexes (S2-S6) with decay time, quantum yield, luminescence, energy band gap and biological properties than parent complex (S1). Interestingly, these ecient properties of complexes may nd their applications in optoelectronic and lighting systems. In addition to these the antioxidant and antimicrobial assays were also investigated to explore the application in biological assays. Investigation of IR, UV-visible and NMR ( 1 H & 13 C) spectra of ligand and complexes in details conrm the formation of complexes. Besides, photoluminescence spectral studies shows that under 356 nm excitation, all synthesized complex exhibits the characteristics peaks at 566 nm, 606nm and 651 nm which can be credited to ( 4 G 5/2 → 6 H 5/2 ), ( 4 G 5/2 → 6 H 7/2 ) and ( 4 G 5/2 → 6 H 9/2 ) electronic transitions of Sm 3+ respectively. The energy band gap and refractive index of all complexes and ligand are determined precisely, which enables the applicability of them in semiconductor devices. Investigation of luminescence decay time in detail provide the homogenous environment around samarium (III) ion with excellent intrinsic lifetime (0.7 2-2.42) of all synthesized complexes. CIE colors coordinates, quantum yield (22.22-74.38) and color purity (98.01-99.04) of all S1-S6 complexes were determined accurately. According to CCT, these complexes are warm in appearance. Energy transfer dynamics validates the successfull transfer of energy from ligand (triplet energy state) to samarium (III) ion (resonating energy states). Biological activities of these complexes display the potential use of these complexes in pharmaceutical eld.


Introduction
In last few decades, lanthanide materials gathered special attention due to their versatile applications in various fields like lasers [1], OLEDs [2], display devices [3], LED bulbs [4] and biological systems [5]. Hence, the synthesis of lanthanides complexes with prominent high quantum yield, large stock shifts and long luminescence decay time has become a hot research topic at present time. Lanthanide complexes possess luminescence due to 4f-4f transitions, which are Laporte forbidden according to spin parity rule [6]. Hence, direct excitation in lanthanides is not beneficial as it results in low molar absorptivity and weak luminescence [7,8]. In order to overcome this catastrophe, a lightharvesting chromophore was incorporated in coordination sphere which absorb energy from an external source and transfers it to lanthanides via antenna effect [9]. Generally, β-hydroxyketone, β-keteocarboxylic acid and aromatic carboxylic acid are vigilantly studied due to their significant ability to transfer the absorbed energy from external source to lanthanides [10,11]. However, β-keteocarboxylic acid is an excellent chromophore to generate excellent emission in lanthanides for display devices and other applications. Further, especially Eu (III), Tb (III) and Sm (III) have unique optical properties such as narrow emission bands, long decay time, large stock shifts and high luminescence due to electronic transitions in emission spectra [12]. Out of these, samarium (III) complexes grab significant attention due to their ability to emit reddish-orange (606 nm) emissions utilized in high-quality display devices.
Currently, six scarlet samarium (III) complexes have been prepared by utilizing 1-cyclopropyl-6-fluro-4-oxo-7-piperazin-1-ylquinoline-3-carboxylic acid (L), bathophenanthroline (batho), 1,10-phenanthroline (phen), neocuproine (neo), 2,2'-bipyridyl (bipy) and 5,6-dimethyl-1,10-phenanthroline (dmph) ligands via grinding technique. All synthesized complexes were investigated utilizing UV-Vis, 13 C-NMR, 1 H-NMR and IR spectroscopy. The information regarding elemental composition and thermal stability were achieved by using elemental and thermogravimetric analysis. The photoluminescent spectra and decay time were executed effectively for reporting the photoluminescent aspects of samarium (III) complexes. The emitting color of complexes was confirmed by colorimetric parameters (color purity and CIE) of complexes. The sensitization of samarium (III) ions by ligand might be well illustrated by the investigation of energy transfer process in detail. To assess the antioxidant and antimicrobial activities, complexes are screened for DPPH and tube dilution techniques respectively.

Reagents and Instruments
All solvents and chemicals were of analytical reagent grade with a stated purity of 99% acquired from a commercial source named Sigma Aldrich and used as such without further purification. The acquisition of the data for measuring excitation and emission spectra of all complexes have been done on Hitachi F-7000 fluorescence spectrophotometer keeping 400 PMT (photomultiplier tube) voltage and slit width 2.5 nm. Each excitation/emission spectra was recorded with scanning rate of 1200 nm/min and response of 0.5 s. The elemental analyses enquired on Perkin Elmer 2400 CHN elemental analyzer. Thermal stability was checked up to 800 °C temperature on SDT Q 600 analyzer with 20 °C/min |in a nitrogen atmosphere. 1 H-NMR and 13 C-NMR spectra were performed on Bruker Avance II spectrophotometer in DMSO at 500 MHz frequency. IR spectra were obtained by Perkin Elmer 400 spectrophotometer using KBr pellet in 4000 cm −1 to 400 cm −1 range. The decay time value was determined via the FL solutions software F-7000 by monitoring the 4 G 5/2 → 6 H 7/2 emission of Sm 3+ ions in solid-state. The UV-Vis absorption spectra were executed on the Shimadzu-2450 spectrophotometer. DPPH and tube dilution techniques were used to investigate the antioxidant and antimicrobial activities respectively.

Preparation of Complexes
To synthesize the complex S1, ligand (0.498 g) and samarium nitrate hexahydrate (0.222 g) were placed in mortar and grinded properly. In order to mix all contents appropriately few drops of water were added and the pH of solution was adjusted at 7 with the help of NaOH (0.01 M) solution. The resulting paste was purified by dissolving in 10 mL water and centrifuged for 2 min; moreover, the same procedure was repeated 2-3 times and dried the resultant sample in oven at 50 o C. The same steps were repeated by adding ancillary ligands such as bipy (0.078 g) S 2, neo (0.104 g) S 3, dmph (0.104 g) S 4, batho (0.161 g) S 5 and phen (0.09 g) S 6 supplemented to the mortar having L and Sm(NO 3 ) 3 .6H 2 O. To portray the energy transfer dynamics triplet state of ligands was considered, for which the same procedure was repeated to prepare corresponding gadolinium complexes. The synthetic route and structure of all samarium (III) complexes utilizing grinding technique were displayed in scheme 1 [13].

Evaluation of Biological Activities
Antioxidant Activities DPPH (2,2-diphenyl-1-picrylhydrazyl) protocol was adopted to compute the antioxidant activities of all referred complexes. The stable free radical DPPH lost its violet color and change into pale yellow due to association with antioxidants moiety, which results a significant drop in absorption at 517 nm on a spectrophotometer. In order to prepare numerous concentrations such as 25, 50, 75 and 100 μg/mL, dimethylsulfoxide (DMSO) was used as a solvent. Further, 1 mL DPPH solution was added to the 1 mL solution of each test sample in their corresponding flasks. The absorbance was recorded after 30-min incubation in dark at 25 °C by taking ascorbic acid as a standard. All tests were performed in triplicate to get concordant values and the scavenging activity of DPPH was expressed in IC 50 (50% of maximum scavenging activity) values. The IC 50 values were determined by graph plotting between scavenging activity (SCA) and numerous concentrations of test samples. By using Eq. 1, the DPPH scavenging activity of all test samples was determined [14]: where A t and A c refers to the absorbance test samples and control reaction respectively.

Antimicrobial Activities
Antimicrobial assays were executed for all title complexes by employing tube dilution protocol [15]. Antibacterial activities of these samples were carried out against the following in vitro gram-negative bacteria: Pseudomonas aeruginosa (MTCC1688), Escherichia coli (MTCC 443) and in vitro gram-positive bacteria: Streptococcus pyogenes (MTCC442), Staphylococcus aureus (MTCC 96). Antifungal activities of these complexes were screened against the fungal strain Candida albicans (MTCC 227), Aspergillus clavatus (MTCC 1323) and Aspergillus niger (MTCC 282). The reference drugs norfloxacin and greseofulvin were used for antibacterial and antifungal activities respectively. All samples (reference + ligand + complexes) were dissolved in DMSO to give a concentration of 200 μg/mL. The incubation period for antibacterial activities was 24 h at 37 °C and for antifungal activities was 7 days at 24 °C for Aspergillus avatus and Candida albicans but 48 h at 37 °C for Aspergillus (1) DPPH scavenge activity (%) = A C − A t A C Scheme 1 Chemical structure and synthetic route for all samarium complexes (S1-S6) niger [16]. The zone of inhibition of antimicrobial activities has been recorded in MIC values.

Results and Discussion
Elemental Analysis  Figure 1 represents the infrared spectrum of complex S1 and free ligand (L), to evaluate the chelation site in bonding. The IR spectra of S 2-S 6 complexes show that all complexes have almost identical IR spectra as displayed in Figure S1 in the supplementary file. The position and intensity of some guide peaks are changed from ligand to complexes, which help to find the binding site in complexes. The broadband scrutinized at 3410 cm −1 depicts the presence of aqua molecule in all synthesized (S1-S6) complexes [17]. In ligand spectra, the band noted at 1711 cm −1 and 1625 cm −1 reflects the existence of carboxylic and ketonic group respectively. It is important to note that the band due to carboxylic acid (1711 cm −1 ) completely disappeared in synthesized complexes, which signalize the chelation through carboxylato group. Additionally, bands due to ketonic group (1625 cm −1 ) shift in all S1-S6 complexes ( Table 2) reveal that the second chelation site is ketonic oxygen. The asymmetric vibrations of carboxylato group appear at 1585-1592 cm −1 and symmetric vibrations of carboxylato group appear at 1370-1375 cm −1 , which are absent in ligand spectra [18]. Further, carboxylate group is a bidentate ligand, hence, can bind either as unidentate or as bidentate by producing a  , demonstrates the unidentate linkage of carboxylic group [19]. The observed ∆ν values for all synthesized S1-S6 complexes are found to be 210-220 cm −1 as enlisted in Table 2, suggesting the unidentate attraction of carboxylato group. Further, the new band appeared at 459-464 cm −1 , 539-548 cm −1 and 1481-1486 cm −1 in S2-S6 complexes assigned for stretching vibrations of ν Sm-O , ν Sm-N and ν C⚌ N respectively in all synthesized complexes as elucidated in Table 2. Figure 2 represents the 1 H-NMR spectrum of free ligand and synthesized complex (S1) carried out in DMSO as a solvent. It was evident from the figure that some significant changes take place when the spectrum of complex was compared with the ligand. The anisotropic property of samarium (III) ions was responsible for upfield and downfield shifts in complexes [20]. The peak observed at 15 ppm manifests the presence of carboxylic group in the ligand, which completely disappeared in synthesized complexes, confirming the chelation of ligand through deprotonated carboxylic acid [21]. In the ligand spectra the peaks observed at 7.56-9.39 ppm (aromatic -CH 2 ), 3.26-3.98 ppm (aliphatic -CH 2 ) and 1.19-1.33 ppm (-CH 3 ) were shifted to 7.54 -8.66 ppm (upfield), 2.39-2.90 ppm (upfield) and 1.18-1.31 ppm (upfield) in complexes respectively. The paramagnetism nature of samarium (III) ions causes upfield shifting of all protons in complexes [22]. Figure S2 in the supplementary file portrays the 13 C-NMR spectrum of L and S1 complex, the carbon values noticed at 176.33 (C = O), 165.81(COOH), 139-153 (aromatic C = C), 106-118 (aromatic C-C) and 35.93-46.26 (-C-C-C-) in ligand spectrum was shifted upfield in corresponding samarium (III) complexes due to paramagnetism of Sm 3+ ion. It was evident from the figure that the peak of carboxylic group in ligand was completely disappeared in complex and the peak of ketonic group in ligand shifts by 7.74-7.86 in all synthesized complexes, which depicts that chelation of L in complexes was through ketonic (C = O) and carboxylic group (COO − ) respectively [23]. Figure 3 depicts the UV-Vis absorption spectra of all S1-S6 synthesized complexes and L (1 × 10 -5 mol/L) by taking DMSO as a solvent. Ligand acts as key absorption for all S1-S6 complexes because absorption displayed by these complexes is weak in the 200-500 cm −1 region. The absorption spectrum of free ligand was investigated by absorption bands with maxima at 280 nm wavelength while the absorption maxima of complexes were positioned at 282 nm (S1), 283 nm (S2), 282 nm (S3), 282 nm (S4), 282 nm (S5) and 283 nm (S6) wavelength. These absorption bands are assigned to π -π* electronic transitions of L [24]. The spectral profile of L and all samarium (III) complexes are analogous to each other, displaying that the excited state of ligand is not disturbed by chelation with samarium (III) ions. It is obvious from the figure that the complex formation shifts the absorption bands to bathochromic shift (red shift) as compared to free ligand. Further, the absorption is also increased in complexes as compared to ligand, which can be explained on the basis of synergistic effect of ligand [25]. Both effects are attributed to the successful chelation of ligand to samarium (III) ions. Furthermore, the encapsulation of the ancillary ligand in S2-S6 complexes upsurges the absorbance as well as saturates the coordination framework.

Spectral Analysis
All results observed from spectroscopic measurements are in good agreement with each other and certify that the chelation of ligand with samarium (III) ions is through carboxylato (COO − ) and ketone groups in all synthesized complexes. Figure 4 reveals the thermal decomposition pattern for the S1 complex since the thermal decomposition pattern exhibited by all synthesized complexes is similar, so, S1 was taken as a representative. The complex S1 exhibited 18% mass loss attributed to the decomposition of 15 water molecules present outside the coordination sphere up to 88 °C. The next loss in mass was 71% accredited to collapsing of complex and removal of two water molecules and three ligand molecules from 242 °C to 557 °C present in coordination sphere (i.e. complex start decomposing) [26]. At last, the    Fig. 2 The 1 H-NMR spectrum of ligand L and its S1 complex  where S denotes scattering coefficient, K represents absorption coefficient and R ∞ refers to the ratio of R The observed values for all S1-S6 complexes and L are catalogued in Table 3. As the table illustrate that the value of energy bandgap is less for complexes in comparison to the ligands, resulting a number of extra electronic states between samarium (III) ions, hence reinforcement of energy transfer increases, so photoluminescence also increases [28]. Therefore, the property of suitable energy bandgap values makes them a promising candidate for semiconductor power appliances. The diffused reflectance spectra of S1-S6 complexes and inset displays its corresponding reflectance spectra Further, in order to find out the refractive index (n) of all S1-S6 complexes precisely, the energy band values are employed by the following relation [29]:

Thermal Analysis
where, n represent the refractive index and E g signifies energy bandgap values, the estimated value for all synthesized are epitomized in Table 3. The refractive index values enable these complexes to be a promising candidate in optoelectronic devices. Figure 6a indicates the excitation spectra of all S1-S6 complexes by monitoring the 4 G 5/2 → 6 H 7/2 electronic transition at 606 nm. Formation of complex extend the π-conjugation, hence, the intramolecular energy transfer from L to Sm 3+ increases by antenna effect, this results in broadening of excitation spectra. The peak found at 360 nm, 374 nm, 404 nm, 453 nm, 472 nm and 495 nm attributed to the electronic transitions arising from ground state 6 H 5/2 to excited state 4 F 9/2 , 4 D 5/2 , 6 P 7/2 , 4 F 5/2 + 4 I 13/2 , 4 G 7/2 , 4 I 7/2 + 4 M 15/2 in samarium (III) ions respectively [30,31] Figure 6b represents the three-dimensional emission spectra of all S1-S6 complexes monitored at the excitation wavelength (356 nm) in solid-state. The luminescence spectra display mainly three peaks at 566 nm, 606 nm and 651 nm which belong to 4 G 5/2 → 6 H j (where j = 5/2, 7/2, 9/2) electronic transition of samarium (III) ions in all synthesized complexes. Out of these, the first transition, 4 G 5/2 → 6 H 5/2 , is magnetic dipole transition, which follows the selection rule of ∆J = 0, where J is total angular momentum, hence the intensity of this peak does not depend on the coordination environment around Sm 3+ ions and 4 G 5/2 → 6 H 7/2 is a mixed transition (partly magnetic and partly electric dipole) but has dominating electric dipole character whereas 4 G 5/2 → 6 H 9/2 is purely electric dipole transitions. The most intense peak of spectra at 606 nm due to hypersensitive 4 G 5/2 → 6 H 7/2 transition is responsible for

Photoluminescence Features
vermillion emission of complexes and makes them suitable for orange light-emitting devices. This transition complies with the selection rule of ∆J = ± 1, The electric dipole transition at 651 nm represents immensely asymmetrical surroundings around Sm3 + ion [32,33]. The upsurge of the photoluminescence from S1 complex to S2-S6 complexes is explained by the introduction of ancillary ligands in place of water molecules which results in increase of radiative rate by diminishing the vibrational quenching caused by water molecules.

Luminescence Decay Curves and Quantum Yield
The average environment surrounding samarium (III) ion was investigated by observing decay time curves under 356 nm excitation and 606 nm emission wavelengths respectively as depicted in Fig. 6c. The emission and excitation slit width were adjusted at 5 nm and PMT voltage at 700 V during measuring the spectra. The luminescence decay time curves were well fitted by monoexponential function and it was derived from the equation given [34]: Herein τ represents the decay time for radiative transitions while I 0 and I represent the integrated intensity of peaks at time 0 and t, respectively. Luminescence decay time curves are best fitted in mono-exponential function, which specifies the homogenous environment around samarium (III) ion in complexes. Further, the total decay time depends upon both radiative and nonradiative as given by the following relation: The observed values of decay time for S 1 (0.72), S 2(1.40), S 3(1.78), S4 (2.02), S 5 (2.41) and S 6 (2.15) are embodied in Table 4. The observed order for decay time in complexes was found to be S1 < S2 < S3 < S4 < S6 < S5, the higher value of decay time in S2-S6 complexes than that of S1 was credited to extended conjugation by the introduction of ancillary ligands. The decay time of complexes purses single exponential behaviour which was responsible for homogenous coordination environment and single luminescent center around the central metal ion.
Quantum yield is an important parameter, utilized to observe the luminescence of samarium (III) ions in complexes [35]. It can be described as the ratio of the numerical quantity of photons emitted to photons absorbed. However, it can be calculated by using the following equation: where ɸ represent quantum yield, τ and τ rad represent the total decay time and decay time for radiative transition. The decay time for radiative transition (τ rad ) of samarium (III) complexes was found to be 3.24 ms for transition 6 G 5/2 manifold for Sm 3+ ions. The observed values reveal an increase in quantum yield for S2 -S6, relative to S1. This can be interpreted due to the synergistic effect of ancillary ligand and lesser nonradiative transition which leads to an increase in luminescence. It is noteworthy to emphasize that the luminescence decay time of the synthesized complexes is higher than most of the reported-[Sm(ligand)3. ancillary] complexes in literature. This fact can be explained on the basis of highly conjugated structure of ligand and ancillary ligands, which extended the conjugation to large extent by decreasing the nonradiative rates since decay time is inversely proportional to radiative and nonradiative Fig. 6 (a) The excitation spectra of all S1-S6 complexes monitored at 606 nm. (b) The emission spectra of all S1-S6 complexes monitored at 356 nm. (c) Luminescence decay curves for all S1-S6 complexes monitored at ʎ EM = 606 nm and ʎ EX = 356 nm transition rates. Moreover, the life time was fetched by observing 4 G 5/2 → 6 H 7/2 emission transition, which was mentioned in Table 5.

Colorimetric Analysis
The emission spectra of luminescence investigation were used to determine the color coordinates (x, y) of all S1-S6 complexes utilizing MATLAB software. CIE (Commission International de I'Elclairge) color coordinates of all S1-S6 complexes are found to be 0.5542, 0.4447 (S1), 0.5560, 0.4430 (S2), 0.5702, 0.4288 (S3), 0.5521, 0.4468 (S4), 0.5558, 0.4432 (S5) and 0.5573, 0.4417 (S6) respectively, enlisted in Table 4. CIE color triangle (Fig. 7), displays the observed color coordinates of all S1-S6 complexes, which authenticate the effective sensitization of Sm 3+ ions by the L in the reddish-orange zone [40]. Amazingly, these bright reddish-orange colors of complexes can be explored in color indicator diodes. Color purity (CP) of all complexes is ascertained by employing CIE color coordinates concerning white light, which shows how actively a meticulous complex acts as a reddish-orange color emitter. CP of all complexes was calculated by using the following relation: In aforementioned equation (x s , y s ) represents color coordinates of S1-S6 complexes, (x i , y i ) refers to white light color coordinates (x i = 0.33, y i = 0.33) and (x d , y d ) represents the dominated color coordinates. CP determined by Eq. 9 is reported in Table 4, which specifies that the color purity of S2-S6 is significantly higher as compared to S1. This fact is explained on the basis of synergic effect of ancillary ligands in place of solvent molecules. Hence, these complexes are proved to be bright orange color emitting materials utilized in OLEDs. Further, an important parameter CCT (correlated color temperature) helps to investigate the quality and nature of light emitted from a light source. Depending on their CCT values, the complexes are cool light source (above 4000 K), warm light source (below 3200 K) and neutral light source (3200-4000 K) [35]. The CCT can be evaluated by applying the Mc-Camy equation: where n can be written as: Here, (x, y) displays the CIE color coordinates of all S1-S6 complexes and (x e , y e ) stands for chromaticity epicenter (0.3320, 0.1858). Observed values of CCT for all S1-S6 complexes are found to be below 3200 K (Table 4) indicating the applicability of these complexes in home appliances as a warm light source.

Energy Transfer Dynamics
The photosensitization is a multistep phenomenon that manifests the excitation of L from ground state to singlet excited state, thereafter energy is transferred to triplet state by intersystem crossing and then to emitting levels of samarium (10) CCT = −437n 3 + 3601n 2 − 6861n + 5514.31 (11) n = x − x e y − y e (III) ions via a nonradiative process. Further, energy transfer from emitting levels to ground levels of samarium (III) ions is responsible for luminescence as portrayed in Fig. 8. It is important to note that there must be a suitable energy gap between ligands and metal ions for effective sensitization, the smaller or larger energy gap leads to weak luminescence due to either back energy transfers or inadequate overlaps among acceptor energy levels. The overlap between the absorption spectrum of ligand and excitation spectrum of complex (S1) displayed in Fig. S3 put in the supplementary file, which indicates the effective sensitization of samarium (III) ions by the L. In order to investigate the energy transfer mechanism, the singlet and triplet state of ligand and ancillary ligands are calculated by referring to the edge wavelength of the absorption spectrum and shortest emission of phosphorescence spectrum of gadolinium complexes respectively. For the same purpose, the absorbance spectrum of dmph and neo is shown in Figs. S4 and S5 in the supplementary file and their inset represent phosphorescence spectra of corresponding gadolinium (III) complexes respectively. Further, to determine the energy values of L, the absorbance spectrum of L is displayed in Fig. 9 and the phosphorescence spectrum of gadolinium (III) complex of the ligand is shown in the inset of this figure. The energy difference between the singlet and triplet state of L is found to be 3320 cm −1 , hence intersystem crossing is not much effective (Empirical rule), which results in internal conversion of energy from ligand to metal ion [41]. Further, Latva's rule states that the energy difference between ligand and lanthanides ions must be 2000-5000 cm −1 for effective energy transfer [42]. Energy differences between singlet and triplet states of ligand and ancillary ligands are found to be 4719 cm −1 (L), 4433 cm −1 (phen), 5233 cm −1 (bipy), 3430 cm −1 (dmph), 4957 cm −1 (neo) and 3333 cm −1 (batho) as tabulated in Table 6 with respect to samarium ion, which are optimum to efficient transfer of energy. Figure 10a represents the percentage scavenging activities of all title complexes with respect to the standard ascorbic acid at 517 nm. The IC 50 values are observed from the plot between scavenging activities (SCA) and different concentrations of samples as portrayed in Fig. 10b and enlisted in Table 7. The larger value of SCA leads to a lower value of IC 50 , resulting in a higher antioxidant capacity of synthesized complexes. The stable free radical of DPPH adopt a diamagnetic character by accepting a proton from antioxidant moiety, hence showing a decrease in absorbance so scavenging activity increases [37]. The antioxidant activities of all S1-S6 complexes are good as compared to ligand, due to the donation of electrons from L → Sm 3+ , which increases the capability of complexes to oxidize. Further, it is evident from the table that the antioxidant activities of S2-S6 complexes are higher than S1, explained on the basis of synergic effect produced by Fig. 8 The systematic energy transfer pathway for [Sm(L) 3 . bipy].6H 2 O complex Fig. 9 The absorbance of ligand spectrum and inset represent the phosphorescence spectrum of corresponding gadolinium complex ancillary ligands. These complexes have excellent antioxidant activities so can be used as an antioxidant agent in the pharmaceutical field. Figure 10c symbolizes the antibacterial activities of all S1-S6 complexes in their corresponding minimum inhibitory concentration (MIC) values against both in vitro gram-positive and in vitro gram-negative bacteria. Further, Table 8 embodied the results observed from antimicrobial (antibacterial and antifungal) activities of all test samples with respect to standard by using the tube dilution technique [36]. The antimicrobial activities of all synthesized complexes are higher than that of ligand due to delocalization of π electrons, which results increase in lipid attraction tendency of L towards Sm 3+ ion. So, Sm 3+ ions can access a deeper extent of microorganism cells and improve antimicrobial activities by slowing the growth of microorganisms [43]. Based on this fact, one can easily see that these complexes are employed as good bactericidal and fungicidal agents in the pharmaceutical field.    L  145  270  180  260  200  800  800  S 1  115  220  120  180  150  210  220  S 2  105  190  115  150  150  220  180  S 3  90  130  125  100  150  180  190  S 4  80  120  62.5  90  140  220  120  S 5  50  90  40  70  120  130  180  S 6  65  110  50  80  130  140  90  STD  10  10  10  10  500  1000  1000