Optical Characterization of Quinoline Yellow Fluorochemosensors for Analyzing Its Photonics Applications With Synthesized Nano Particles

Quinoline Yellow (QY) with the scientic name [sodium 2-(2, 3-dihydro-1,3-dioxo-1H-inden-2-yl) quinoline-6,8-disulfonate] (SQDS) is investigated for its sensing properties as uorochemosensors and its NLO applications. Pure SQDS is doped with copper ferrite and cerium oxide nanoparticles and studied for changes in spectral results. Change in absorption spectrum is observed depending on the polarity of solvents. Intensity of uorescence also varies with different type of solvents. Optical characterization for SQDS is carried out via various spectroscopic techniques including UV-VIS spectroscopy, FTIR spectroscopy, Scanning Electron Microscopy and Photo Luminescence (PL) spectroscopy. Optical parameters like extinction coecient, refractive index and bandgap energy are determined from absorption spectrum for both solution and lm samples. XRD characterization is also performed for QY and for nanoparticle doped QY. For investigating Non-Linear optical (NLO) application of QY, lms are prepared and optical imaging is performed via Atomic Force Microscopy (AFM). Characterization results are analysed and predicted for application in non-linear optics.


Introduction
A molecular sensor is also called chemosensor. These are molecules which is used for detection of ions by interaction with an analyte. There are two main parts of a chemosensor, one is the receptor and other is reporter. The reporter gives out any change in signal caused when the guest is binding to the receptor. Fluorescent chemosensors use uorescence as an output signal change to detect presence of ions.
These sensors are considered powerful tool for detection because they are highly sensitive, simple and used as real-time situ imaging. Quinoline moieties are bioactive compounds. Quinoline derivatives are extensively studied because of their wide range of application which includes antibacterial, antiin ammatory, anti larial, antifungal, local anaesthetic agents. Quinoline derivatives are found to have exceptional mechanical properties, which contributes to generation of high e cient materials in transportation of electrons. Characteristics such as good lm formation, high electron mobility, great e ciency for photoluminescence and high thermal stability, makes quinoline derivatives to be of application in OLEDs .So, compounds containing quinoline owes to improved brightness and luminescence e ciencyin organic light emitting diodes [1][2][3][4][5][6][7][8], [18][19][20][21][22][23][24][25][26].
Organic crystals contains electron acceptor and donor groups on either side of conjugated π-bond. Mobility is increased as a result of overlapping between π orbits and delocalized electronic charge.
Increase in optical non-linearity happens when electron charge density distribution is enhanced in excited state or ground state. NLO applications of quinoline derivatives are signi cantly studied and investigated [9][10][11][12][13]. Ultrafast responses, low dielectric constant and broadband electronic responses are the key properties responsible for its non-linear optical properties (NLO). Quinoline moiety acts as electron acceptor and show high rst order hyperpolarization. Quinoline based crystals that are optically nonlinear have been found to exhibit exceptionally high macro and microscopic non-linear optical susceptibility in addition to good environmental and thermal stability [14][15][16][17], [27].
In this present work, we investigate quinoline yellow derivative, SQDS [sodium 2-(2,3-dihydro-1,3-dioxo-1Hinden-2-yl) quinoline-6,8-disulfonate] with the help of spectroscopic methods namely UV-VISible spectroscopy and FTIR spectroscopy. XRD for pure SQDS is performed and is compared with XRD of mixed samples of SQDS with nanoparticles of copper ferrite and cerium oxide. Scanning electron microscopy is also performed for pure and nanoparticle doped SQDS. For investigating non-linear optical properties, lms are made with solvent and SQDS and is compared using UV-Visbile and FTIR spectroscopic techniques. Film samples are tested under Atomic force microscope to study surface morphology and structure and uniformity of samples. Photoluminescence spectra is carried out for nanoparticle doped and pure powdered samples.
Nano particles of copper ferrite and cerium oxide is synthesized in our lab and was used for doping the pure powder samples for spectroscopic analysis. Spectroscopy is done for the compound to understand and study its optical characteristics so as to identify its scope in luminescence applications. UV-Visible spectroscopy is carried out using Shimadzu UV-1800 and the solvent used was Dimethyl Sulfoxide (DMSO). The quinoline derivative SQDS is found to have complete solubility in DMSO and water. FTIR spectroscopy is one for sample in solution form and lm form on Spectrum 3 FTIR spectrophotometer. XRD using D8 XRD and SEM using Tescan Vega 3 is carried out for powdered samples of pure quinoline and compared with mixture of pure quinoline in cerium oxide and copper ferrite. Film samples are prepared through drop casting method using DMSO as solvent. The concentration used for preparation of lm samples is 0.1%. Solution of SQDS in DMSO is heated on magnetic stirrer for 20 mins at 70 degree Celsius and 500 rpm. Then the solution is dropped on a clean glass slide and heated in oven at 50 degree Celsius so that DMSO can evaporate and we can get SQDS lm. AFM is carried out for studying the surface morphology of lm samples. Also, photoluminescence of pure SQDS and nanoparticle doped SQDS is analyzed using FP-8300 JARCO for PL spectra determination 2.2 Synthesis of copper ferrite nanoparticles: Copper ferrite was prepared by solution combustion method using freshly prepared Oxalyl Dihydrazine (ODH) as a fuel. Stochiometric calculation was adopted to balance the equation as mentioned below:-2.416 g Cu(NO3)2 + 8.09 g Fe(NO3)3+ 4.7238 g ODH+ 25 ml of double distilled water. was used to obtain CuFe2O4 compound. The precursors were mixed in the crystalline dish and subjected to magnetic stirring for 20 minutes. After the proper mixing, it is transferred to the Muffel furnace which is preheated at 400°C . within 20 minutes of time the smoldering ame was observed and burn completes the reaction. Here the ratio of reducing and oxidizing valencies were kept 1. Fig. 1(b) shows molecular structure for copper ferrite nanoparticles.

XRD.
The crystal structures of the powder samples at a scanning rate of 0.02 per second in the range of 20 to 80 using D8 XRD model in CAMT department, MSRIT, Bangalore. Graphs and peak analysis was done using origin software.

FT-IR.
The IR absorption bands of samples in the range of 4000 to 400 cm −1 pellets were analyzed using using Spectrum 3 FTIR spectrograph in BMSIT, Bangalore.

Photoluminescence Spectra
Fluorescence is performed using Model name: FP-8300 with Xe lamp in medium sensitivity for the range 242-897 nm at Mysore University, Mysore.

AFM and SEM
Atomic force microscopy was performed for lm samples at various inclinations in IISC, Bangalore.
Scanning electron microscopy was performed for powdered samples in BMSCE, Bangalore.

UV-Visible Spectroscopy Analysis
UV-Visible spectrum for solution sample and lm sample of SQDS in solvent DMSO is shown in Fig. 2. Positive solvatochromism effect is observed in absorption peaks. Absorption peak for lm sample shifts to longer wavelength region due to increase in solvent polarity. This phenomenon is also called red shift or bathochromic shift. Most of the DMSO has evaporated in lm sample and hence a change in absorbance value is also observed. There is a hypochromic effect in lm samples as compared to liquid solution samples. Hypochromic effect is the phenomenon when there is decrease in intensity of absorption. Optical density peaks are found at 354 nm for solution sample and at 452 nm for lm samples.

FTIR Spectroscopy Analysis
FTIR results for SQDS in solution form and in lm form are illustrated in Fig. 3(a) and Fig. 3(b) respectively. Infrared absorption spectrum is produced to identify chemical bonds in molecule. The obtained spectrum is a unique pro le for every sample and consists of molecular ngerprint which can be used for identifying molecules in different samples. Two types of analysis can be done with FTIR spectrum-functional group region and ngerprint region. Below 1500 cm −1 in the obtained infrared spectrum gives the ngerprint of the sample. However it is not reliable for studying about the chemistry of molecules. Above 1500 cm −1 in the spectrum is signi cant as it gives information about functional groups present in the sample. Table 1 shows functional groups.

XRD Analysis
XRD plots for pure SQDS and copper ferrite doped SQDS and pure SQDS and cerium oxide doped SQDS is shown in Fig. 4(a) and Fig. 4(b) respectively. Material is irradiated with X-rays and the intensities are recorded with respect to the scattering angle at which it leaves the sample. XRD peaks give information about the atomic distribution in unit cell and the XRD pattern provides information on defects and particle size. Samples are grinded into ne powder and then analyzed. Peak width is inversely proportional to crystal size. Sharp peaks corresponds to crystallinity and soft peaks represents amorphous form in the sample. Change in peaks due to doping represents parameter change in unit cell. XRD for copper ferrite is shown in Fig. 4(c).

Photoluminescence Spectra Analysis
Photoluminescence Spectra for pure SQDS, copper ferrite doped SQDS and cerium oxide doped SQDS is shown in Fig. 5(a), Fig. 5(b) and Fig. 5(c) respectively. Material under analysis is stimulated with photon of excitation wavelength of 354 nm. This causes photo-excitation in the sample and in turn it causes electron to jump to higher state and then release photon to come back to ground state. This emission of light is called photoluminescence. Emission is monitored at a xed excitation wavelength observed from absorption spectrum. The area under the curve gives value for bandgap energy. PL spectra for pure nano particle of copper ferrite and cerium oxide is shown in Fig. 5(d) and Fig. 5(e) respectively.

AFM Analysis
AFM for lm sample is shown in Fig. 6(a) and Fig. 6(b). AFM is a no-contact probing microscopy imaging technique with near atomic resolution to study surface topology. Surface roughness is quanti ed and uniformity of lm samples is understood. Low rms is observed in lm samples which shows uniformity of surface.

SEM Analysis
SEM for powdered samples of pure SQDS, copper ferrite doped SQDS and cerium oxide nanoparticle doped SQDS is illustrated in Fig. 7, Fig. 8 and Fig. 9. This imaging techniques is used for studying topology of surface for the samples. SEM uses electron to take images. Cross section of particles is observed whether the particle are porous, hollow or solid.
Absorption spectrum is used for determining optical parameters like extinction coe cient Fig. 10, refractive index Fig. 11 and band gap energies Fig. 12.

Absorption and emission spectrum in different solvents
Absorption and emission spectrum for Quinoline Yellow is tested in four different solvents namely water, ethanol, methanol and dimethylsulfoxide. With increase in solvent polarity, there is an observable red shift in absorption wavelength. This bathochromic shift in absorption is due to change in solvent polarities.
With increase in polarity of solvent, absorption peaks tends to shift towards longer wavelength. Also, emission spectrum undergoes change due to solvent polarity. Fig. 13 and Fig. 14 shows solvent effect on absorbance and uorescence of the compound.

Conclusion
With all the spectroscopic method for characterization of SQDS, it can be deduced that presence of solvatochromism re ects presence of auxochromes in sample. Red shift con rms auxochromes and that in turn leads to presence of conjugation in molecules. FTIR illustrated no dramatic introduction or elimination in transmission peaks which means it does not show signi cant changes in chemistry of samples when converted into lms. XRD showed crystallinity of samples owing to sharp peaks and it could further be used for determining the unit cell lattice dimensions. PL spectra showing high intensity peaks make the sample to be a good volunteer for laser dyes. SEM also gives clear resolution images which shows good topology of surface. AFM con rms low roughness and uniformity in lm sample. This makes it a good candidate for non-linear optical applications. Dependence of absorption and emission spectrum on solvent polarity con rms presence of uorophores and auxochromes which can have a signi cant scope in luminescence applications.       SEM image for pure cerium oxide Solvent effect on uorescence spectrum