**6.1 Bioimaging applications**

A variety of Schiff base probes with fluorescent sensors are used for bioimaging applications to detect metal ions. Most of the fluorescent probes selectively and sensitively detect only one or two metal ions. Schiff base probes detect analytes in non-aqueous or semi-aqueous media, making them useful for the detection and monitoring of toxic ions in drinking water and industrial waste [100]. A simple and versatile Schiff base chemical sensor was developed to detect four adjacent series 4 metal ions (Co2+, Ni2+, Cu2+, and Zn2+) by colorimetric or fluorometric methods. This chemical sensor has been used to image Zn2+ in HepG2 cells, zebrafish, and tumor-bearing mice, demonstrating potential biological applications [101]. The fluorescence sensor synthesized from the reaction of picolinohydrazide and 4 (diethylamino) salicylaldehyde successfully detected Al3+ and Zn2+ in living cells, suggesting that this simple biosensor has great potential for biological imaging applications [102].

*Schiff Base in Organic, Inorganic and Physical Chemistry*






 *bases.*

Compound (E)-1-((L-glutaminoimino) methyl)naphthalene-2-ol (A) showed good solubility and compatibility in the presence or absence of Al3+ and showed some fluorescence in human Hs27 epithelial cells. Bioimaging has been reported [4]. Fluorescent Schiff base organotin dyes (1: Et2N-L-SnPh2, 2: Et2N-L-SnBu2, 3: MeO-L-SnPh2, 4: MeO-L-SnBu2, 5: HO-L-SnPh2, and 6: HO L-SnBu2, L = 2-hydroxybenzylidene-4-hydroxybenzhydrazine) showed efficient two-photon excitation (1–4). Two of the compounds (5 and 6) were found to be able to selectively accumulate in HeLa cells, allowing their differentiation from normal cells (periodontal ligament cells) [103, 104].

### **6.2 Phosphorescent OLEDS**

Five one-armed Schiff base ligands HL1, HL2, HL3, HL4, and HL5 were obtained from condensation of various group-substituted salicylaldehydes with aniline and 2,4,5-trifluoroaniline gave. Their platinum(II) complexes Pt(L1)2, Pt(L2)2, Pt(L3)2, Pt(L4)2, Pt(L5)2, and PtL5 DMSO obtained by the metalation of ligands with K2PtCl4 were found to be excellent candidates for phosphorescent OLEDs [105]. The luminescent performance of azomethine zinc complexes in organic light-emitting diodes has been investigated, and the results have shown excellent electroluminescence properties as blue fluorescent light sources [106]. Schiff-base zinc metal complexes have been developed to serve as efficient light-emitting materials for optoelectronic applications such as organic light-emitting diodes. These zinc complexes serve as promising emissive layers for optoelectronic applications [107].

## **6.3 Sensing applications**

Fluorescence on/off sensor of a wide range of Schiff bases is being developed for determination of various analytes, toxic ions, and metallic cations and anions in different types of environmental and biological media [108].

Biosensor: Conductive hydrogels based on graphene oxide, dopamine, and polyacrylamide were prepared using the Schiff bases. The high elongation, toughness, and self-adhesion of conducting hydrogels have provided great advantages as biosensors [109].

In forensics, Schiff bases are primarily used in the analysis of illicit drugs. Chemical reactions with Schiff bases reveal illicit drug production and help determine analytes in confiscated samples [110, 111].

#### **6.4 Tissue regeneration**

Various substituted Schiff bases have enhanced bulk modulus of the composite hydrogels and slightly increased the in vitro degradation rate. It also promoted cell adhesion and proliferation and maintains the regular cell morphology of bovine articular chondrocytes, increasing potential applications in cartilage tissue engineering [109].

#### **6.5 Bioprint**

Water-soluble hydroxybutyl chitosan (HBC) and chondroitin oxysulfate (OCS) have been used to generate bioinks based on the Schiff base reaction, using different sacrificial molds in 3D bioprinting techniques to produce different structures of

hydrogels. The controllable shape of HBC/OCS bionic hydrogels can be optimized and customized for specific cartilage engineering applications [109].

#### **6.6 Tissue adhesion**

Aldehyde groups in hydrogels based on the Schiff reagent can promote the adhesion of hydrogels to surrounding tissues. An injectable double-cross-linked selfhealing hydrogel based on dopamine-grafted oxidized sodium alginate (OSA-DA) and polyacrylamide (PAM) for wound healing has been reported. In terms of hydrogen bonding and Schiff base bonding, the self-healing OSA-DA-PAM hydrogel possesses stable mechanical properties such as high tensile strength and elongation. In addition, numerous catechol groups on OSA-DA chains can endow hydrogels with unique cell affinity and tissue adhesion [10]. In situ forming hydrogel, derived from natural polysaccharides through Schiff base reaction, can be modulated and prepared for soft tissue adhesive, hemostasis, or other biomedical applications in future [110].

#### **6.7 Dyes**

New complexes of Zn(II), Pd(II), and Pt(II) with Schiff bases are metal salts of 4- (dibutylamino)-2-hydroxybenzaldehyde and 4,5-diaminophthalonitrile. Sensor applications for imaging surface temperature (planar optodes) and monitoring rapid temperature changes (fiber optic microsensors) have been demonstrated. Pt(II) complexes immobilized in gas permeable matrices also turned out to be promising materials for oxygen measurements. [112].

Schiff bases based on salicylaldehyde units and their use as metal-free organic chromophores can be used to sensitized and co-sensitize dye-sensitized solar cells (DSSCs) [113].

Compounds Et2N-L-SnPh2 and MeO-L-SnPh2 act as an excellent staining for cancer cells (HeLa) using two-photon bioimaging and are expected to have biomedical applications [104].

### **7. Future prospectus**

From the discussion in the section of biological evaluation of Schiff bases, it was clear that the pharmacophore possesses various biological activities, which can be again explored more against various diseases. New groups of organic compounds are still being described, the combinations of which may form a group of extremely desirable compounds with higher potential. The biologically active Schiff's base ligands and metal complexes are playing very crucial role in the drug discovery [114]. Medicinal chemists are now interested in developing novel chemotherapeutic Schiff bases and their metal complexes.

Apart from this, conjugated Schiff Bases have been employed in electronics such the organic field-effect transistor, Perovskite solar cells, and electrochromic devices because they offer some intriguing optoelectronic features. These are also employed in the production of covalent organic framework, which is used in the storage of gas [115]. The measurement of pH values has evolved into one of the most essential necessities with the recent advancements in biological and environmental research. Because of their smooth synthetic roots, easily tuneable structural architecture, nondestructive signals of emission, visually differentiable color generation, and capacity

for real sample analysis, organic Schiff base compounds and their derivatives have been observed to play crucial roles in determining the pH values of a particular medium [116]. Because of its bioactive core, Schiff bases have a wide range of applications in the chemical, food, coordination, medical, agricultural, and other industries. This body of literature made it very evident that there will be several opportunities for Schiff bases to become active research molecules in the future.

### **8. Conclusion**

Schiff bases are integral core of the organic chemistry having a verity of biological activities. This chapter focused on the novel leads of numerous Schiff bases having potential medicinal activities with lesser side effects. At last decades, the researchers perceived attention toward bioactive core of Schiff bases, which gained wide medicinal interest. This chapter also explored industrial application of Schiff bases. Advances in this era will require access of the structure activity relationship and mechanism of action of the Schiff bases containing compounds.

At present scenario, Schiff bases are perceived importance in biological activity. It is a versatile organic compound, which is synthesized in reaction between amino compound and aldehyde or ketone well known as imine by condensation process. This imine or azomethine functional groups are versatile pharmacophores for design and development of various bioactive lead compounds. Schiff bases are extensively used for biological activities such antimicrobial, anthelmintic, anti-inflammatory, anticonvulsant, antiTB, antineoplastic, and antidepressant activities. Also, Schiff bases have an intermediately compound in synthesis of various organic compounds. It is also used as catalyst, pigments, and dye synthesis. Furthermore, Schiff bases are used as corrosion inhibitors. The metal complexes of Schiff bases have diversified biological activities. The present chapter summarized the information with respect to diverse biological activities and depicted the recent synthesized variety Schiff bases as potential bioactive core.

## **Conflict of interest**

We confirm that there is no conflict of interest.

## **Author details**

Ruchi Shivhare\*, Kishor Danao, Deweshri Nandurkar, Vijayshri Rokde, Ashwini Ingole, Amol Warokar and Ujwala Mahajan Dadasaheb Balpande College of Pharmacy, Nagpur, Maharashtra, India

\*Address all correspondence to: shivharer4@gmail.com

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
