**2. Applications of porphyrins and hemeproteins in spintronics**

## **2.1 Porphyrins and derivatives**

Single-molecule spintronic devices have gained crescent interest for the use in advanced electronic systems. The question is to find molecular structures which, as single molecule, can exhibit the desirable properties of spintronics such as spin valve [55–60], spin crossover [61–63], spin filtering [64–66], Kondo effect [67], and others. In the literature, porphyrins and derivatives have been described as promising candidates for molecular devices, once they have unique electronic properties [68]. Theoretical and experimental studies on the charge transport of porphyrin-based derivatives have demonstrated desirable physical properties for single-molecule spintronic such as current switching, long-range electron tunneling, current rectifying, and others [55, 69–71]. Several studies have corroborated the potential of porphyrin application in spintronics. Self-assembled porphyrin nanorods showed the mediated conduction through a UHV-STM image with differing HOMO- and LUMO-mediated conductions. The authors demonstrated a conductivity by barrier-type tunneling through distances less than 10 nm and long-distance conduction occurring only through the LUMO band. The selfassembled porphyrin nanorods are an efficient rectifying device that converts alternating current (AC), i.e., a current that periodically inverts direction, to direct current (DC), which moves in a unique direction [72]. In another study, the electronic transport of a nanowire composed by porphyrin-ethyne-benzene conjugates had its effective conductivity assigned to the coplanar conformation of phenyl and porphyrin moieties. The coplanar structure that allows amino or nitro substituent at the meta-position of the phenyl bridge that connects the π-system can provide higher current ratios of the on/off states. The switch effect of meta-substituents in the coplanar conformation disturbs the whole molecule

**149**

**Figure 4.**

*modified from Cho et al. [73].*

*Technological Applications of Porphyrins and Related Compounds: Spintronics and Micro…*

while having only a local impact on the system with a perpendicular conformation. The nanowires formed by π-conjugated systems have potential for switch devices tunable by substituents [69]. Another evidence of porphyrin application in electronic devices was reported by Sedghi et al. [71]. Nanowires formed by porphyrin molecules linearly oligomerized (oligo-porphyrin wires) can mediate temperature-dependent electron transport. The study showed that the system conductance has temperature dependence and it suggests a long-range electron tunneling [71]. For application in spintronic devices, Cho et al. [73] proposed a theoretical organometallic framework formed by one-dimensional infinite chromium porphyrin array in which chromium atoms are located in a straight line (**Figure 4a**). The system exhibited spin filter property when the simulations were carried out with dimeric form, Cr-PA2, between Au electrodes (**Figure 4b**).

The fabrication of spin-dependent electronics, the spintronic devices, requires the external control of the magnetization of the that behaves like a magnet. In this regard, the paramagnetic porphyrin molecule is a promising active building block for spintronic devices. Wende et al. [74] studied by experimental and theoretical approach paramagnetic iron porphyrin molecules bound on ferromagnetic Ni and Co films on Cu(100). The authors investigated the porphyrin structural orientation and the magnetic coupling with the substrate. The porphyrin molecules associated with the substrate Co or Ni were ordered ferromagnetically. In the device, the magnetic moment of the porphyrin iron could be rotated in the plane and out of the plane by a magnetization reversal of the substrate. In a similar study, Scheybal et al. [75] also associated porphyrins with metallic films and studied X-ray magnetic circular dichroism (XMCD). In this case, the researchers used manganese (III) tetraphenylporphyrin chloride (MnTPPCl) molecules adsorbed by cobalt substrate

*Examples of nanowires formed by porphyrins. (a) Theoretical organometallic framework built by onedimensional infinite chromium porphyrin array in which chromium atoms are parallel, the M–Pan; (b) a dimeric form, Cr–PA3, linked to two Au (111) electrodes PA2 via Au–S bond. Structures of nanodevices* 

*DOI: http://dx.doi.org/10.5772/intechopen.86206*

### *Technological Applications of Porphyrins and Related Compounds: Spintronics and Micro… DOI: http://dx.doi.org/10.5772/intechopen.86206*

while having only a local impact on the system with a perpendicular conformation. The nanowires formed by π-conjugated systems have potential for switch devices tunable by substituents [69]. Another evidence of porphyrin application in electronic devices was reported by Sedghi et al. [71]. Nanowires formed by porphyrin molecules linearly oligomerized (oligo-porphyrin wires) can mediate temperature-dependent electron transport. The study showed that the system conductance has temperature dependence and it suggests a long-range electron tunneling [71]. For application in spintronic devices, Cho et al. [73] proposed a theoretical organometallic framework formed by one-dimensional infinite chromium porphyrin array in which chromium atoms are located in a straight line (**Figure 4a**). The system exhibited spin filter property when the simulations were carried out with dimeric form, Cr-PA2, between Au electrodes (**Figure 4b**).

The fabrication of spin-dependent electronics, the spintronic devices, requires the external control of the magnetization of the that behaves like a magnet. In this regard, the paramagnetic porphyrin molecule is a promising active building block for spintronic devices. Wende et al. [74] studied by experimental and theoretical approach paramagnetic iron porphyrin molecules bound on ferromagnetic Ni and Co films on Cu(100). The authors investigated the porphyrin structural orientation and the magnetic coupling with the substrate. The porphyrin molecules associated with the substrate Co or Ni were ordered ferromagnetically. In the device, the magnetic moment of the porphyrin iron could be rotated in the plane and out of the plane by a magnetization reversal of the substrate. In a similar study, Scheybal et al. [75] also associated porphyrins with metallic films and studied X-ray magnetic circular dichroism (XMCD). In this case, the researchers used manganese (III) tetraphenylporphyrin chloride (MnTPPCl) molecules adsorbed by cobalt substrate

#### **Figure 4.**

*Solid State Physics - Metastable, Spintronics Materials and Mechanics of Deformable...*

**2. Applications of porphyrins and hemeproteins in spintronics**

*Self-propelling mechanisms of Janus micromotors. The photocatalytic mechanisms are represented by the three first representations. The formation of a concentration gradient of superoxide ions and bubbles results from the oxidation of hydrogen peroxide in solution. In the right image, irradiation with infrared light on the nanostructured gold layer creates a thermal gradient due to the plasmonic effect. Warming promotes agitation* 

Single-molecule spintronic devices have gained crescent interest for the use in advanced electronic systems. The question is to find molecular structures which, as single molecule, can exhibit the desirable properties of spintronics such as spin valve [55–60], spin crossover [61–63], spin filtering [64–66], Kondo effect [67], and others. In the literature, porphyrins and derivatives have been described as promising candidates for molecular devices, once they have unique electronic properties [68]. Theoretical and experimental studies on the charge transport of porphyrin-based derivatives have demonstrated desirable physical properties for single-molecule spintronic such as current switching, long-range electron tunneling, current rectifying, and others [55, 69–71]. Several studies have corroborated the potential of porphyrin application in spintronics. Self-assembled porphyrin nanorods showed the mediated conduction through a UHV-STM image with differing HOMO- and LUMO-mediated conductions. The authors demonstrated a conductivity by barrier-type tunneling through distances less than 10 nm and long-distance conduction occurring only through the LUMO band. The selfassembled porphyrin nanorods are an efficient rectifying device that converts alternating current (AC), i.e., a current that periodically inverts direction, to direct current (DC), which moves in a unique direction [72]. In another study, the electronic transport of a nanowire composed by porphyrin-ethyne-benzene conjugates had its effective conductivity assigned to the coplanar conformation of phenyl and porphyrin moieties. The coplanar structure that allows amino or nitro substituent at the meta-position of the phenyl bridge that connects the π-system can provide higher current ratios of the on/off states. The switch effect of meta-substituents in the coplanar conformation disturbs the whole molecule

**2.1 Porphyrins and derivatives**

*of water molecules that generate one-way movement.*

**Figure 3.**

**148**

*Examples of nanowires formed by porphyrins. (a) Theoretical organometallic framework built by onedimensional infinite chromium porphyrin array in which chromium atoms are parallel, the M–Pan; (b) a dimeric form, Cr–PA3, linked to two Au (111) electrodes PA2 via Au–S bond. Structures of nanodevices modified from Cho et al. [73].*

film. The results demonstrated that the film substrate induced a net magnetization on the porphyrin. Chen et al. [76] made calculations of conductance in a ferrous porphyrin. The study showed that the conductance of the iron porphyrin is tuned by mechanical distortion of the porphyrin plane and shifts the coupling state from the low spin to excited spin states. These properties of the system are interesting for sensing applications. Systems containing molecules with switchable spins are promising for the fabrication of materials with spintronic properties. Organometallic molecules such as porphyrins can be switched to on and off magnetic states when associated with the ferromagnetic substrate. Wäckerlin et al. [77] described that cobalt(II)tetraphenylporphyrin (CoTPP) ferromagnetically coupled to nickel thin film (Ni(001)) is switchable from on to off state of Co spin by the complexation with NO that is a spin trans effect. NO coordinates with Co2+ leading to the formation of a NO-CoTPP nitrosyl complex that is the off state of the Co spin. The system is restored to the *on* state when NO is thermally dissociated from the nitrosyl complex. Li et al. reported the construction and magnetic characterization of a fully functional system formed by the hybridization of a single magnetic porphyrin molecule with graphene nanoribbons. The fusion of the porphyrin core into graphene through the formation of new carbon rings at chemically predefined positions was demonstrated by scanning tunneling microscopy of high resolution. The authors also demonstrated that porphyrin retains the magnetic functionality and the magnetic anisotropy is modulated by the structure of the contacts [78]. In another study, Lewandowska et al. report a simple and efficient method for the fabrication of porphyrin-graphene oxide hybrids. The hybrid system has donoracceptor properties and exhibits charge transfer between porphyrin and graphene oxide. The non-covalent interaction between the porphyrin and graphene oxide changes intensely the magnetic properties. The dramatic change in the magnetic properties probably is due to refined tuning of graphene domain magnetism that can be promoted by the modulation electron density produced by electron donor or electron acceptor substituents [79].

#### **Figure 5.**

*Chiral-induced spin selectivity (CISS) effect in cytochrome c. cartoon of the spin-filtered electron transport through the chiral a-helix of cytochrome c as reported by Michaeli et al. [82]. Horse heart cytochrome c structure was obtained from protein data Bank, code 1HRC.*

**151**

*Technological Applications of Porphyrins and Related Compounds: Spintronics and Micro…*

The presence of the iron protoporphyrin IX as the prosthetic group of hemeproteins endows these proteins of electronic and magnetic properties that can be applied in spintronics. The hemeproteins have an additional property that is the folding in chiral structures. [80]. The chiral structures such as the α-helices present in cytochrome *c* (**Figure 5**), for instance, can act as spin filters and respond for the chiral-induced spin selectivity (CISS) effect. To date, cytochrome *c* has been the

New types of spin-dependent electrochemistry measurements have been applied to probe the spin-dependent charge transport properties of nonmagnetic chiral molecules such as cytochrome *c*. Besides cytochrome *c*, the photosystems that are complexes of proteins associated with a non-heme porphyrin, the chlorophyll, also have electron transport capacity with spin selectivity [81, 82]. When the measurements were carried out with different orientations of the PSI protein complex, the dependence of spin polarization with the electron transfer path in photosystem I was proven [81, 82].

**3. Application of porphyrins and hemeproteins in the construction** 

Several studies have been developed to produce nanodevices containing porphyrins with a potential use in MNRs to be applied in theranostics. According to Li et al. [83], porphyrins have a diversity of properties applicable to health preservation, diagnosis, and treatment. Porphyrins can amplify signals for magnetic resonance imaging (MRI), positron emission tomography (PET), infrared fluorescence imaging, and dual modal PET-MRI. Porphyrins have chemical and physical properties that allow the application of these compounds in the detection and destruction of tumors. Porphyrins can efficiently convert light into electronic excitation of molecular oxygen to produce singlet oxygen in photodynamic therapy (PDT) or light to heat for photothermal therapy (PTT). Therefore, porphyrins have been applied in the treatment of solid cancers and ocular vascularization diseases [29]. Also, there are some studies about porphyrin-nanoparticle systems employed in dentistry treatment [84–87]. These systems can be used in the diagnosis of cancer by acting, for instance, as biosensors that exhibit affinity for a single molecule converting biochemical to electrical signals, detection of salivary biomarkers of oral tumors, and others [85, 88]. The capacity of self-assembly in a range of supramolecular aggregates is a crucial property for the application of porphyrins to construct MNRs [29, 89]. Ion et al. [89] demonstrated that porphyrins could self-assemble in several types of supramolecular aggregates such as linear head to tail, J-aggregates, and fractal aggregates with diverse and definite photophysical properties (**Figure 6**) [89]. The study of Ion et al. showed nanotubes formed by porphyrins and the importance of this technique for brain aneurysm instrumentation. They used meso-5, 10, 15, 20-sulfonate-phenyl porphyrin (TPPS4) and observed the formation of organized nanostructures by ionic self-assembly. Neurons and glial cells incubated with porphyrin nanotubes formed interconnected networks featured on the nanotube templates. The capacity of TPPS4 to form nanotubes by self-assembly demonstrates the potential of this porphyrin in the fabrication of NMRs applied to medicine. MNRs must have the capacity to self-propel that could be provided by a diversity of materials and mechanisms. Park et al. describe the fabrication of "swimmers": microstructures with autonomous mobility at water/air interface. The particles of porphyrin-based

*DOI: http://dx.doi.org/10.5772/intechopen.86206*

unique hemeprotein used for spin filtering [28, 33, 38].

**and working of micro-/nanorobots**

**3.1 Porphyrins and derivatives**

**2.2 Hemeproteins**

*Technological Applications of Porphyrins and Related Compounds: Spintronics and Micro… DOI: http://dx.doi.org/10.5772/intechopen.86206*

#### **2.2 Hemeproteins**

*Solid State Physics - Metastable, Spintronics Materials and Mechanics of Deformable...*

film. The results demonstrated that the film substrate induced a net magnetization on the porphyrin. Chen et al. [76] made calculations of conductance in a ferrous porphyrin. The study showed that the conductance of the iron porphyrin is tuned by mechanical distortion of the porphyrin plane and shifts the coupling state from the low spin to excited spin states. These properties of the system are interesting for sensing applications. Systems containing molecules with switchable spins are promising for the fabrication of materials with spintronic properties. Organometallic molecules such as porphyrins can be switched to on and off magnetic states when associated with the ferromagnetic substrate. Wäckerlin et al. [77] described that cobalt(II)tetraphenylporphyrin (CoTPP) ferromagnetically coupled to nickel thin film (Ni(001)) is switchable from on to off state of Co spin by the complexation with NO that is a spin trans effect. NO coordinates with Co2+ leading to the formation of a NO-CoTPP nitrosyl complex that is the off state of the Co spin. The system is restored to the *on* state when NO is thermally dissociated from the nitrosyl complex. Li et al. reported the construction and magnetic characterization of a fully functional system formed by the hybridization of a single magnetic porphyrin molecule with graphene nanoribbons. The fusion of the porphyrin core into graphene through the formation of new carbon rings at chemically predefined positions was demonstrated by scanning tunneling microscopy of high resolution. The authors also demonstrated that porphyrin retains the magnetic functionality and the magnetic anisotropy is modulated by the structure of the contacts [78]. In another study, Lewandowska et al. report a simple and efficient method for the fabrication of porphyrin-graphene oxide hybrids. The hybrid system has donoracceptor properties and exhibits charge transfer between porphyrin and graphene oxide. The non-covalent interaction between the porphyrin and graphene oxide changes intensely the magnetic properties. The dramatic change in the magnetic properties probably is due to refined tuning of graphene domain magnetism that can be promoted by the modulation electron density produced by electron donor or

*Chiral-induced spin selectivity (CISS) effect in cytochrome c. cartoon of the spin-filtered electron transport through the chiral a-helix of cytochrome c as reported by Michaeli et al. [82]. Horse heart cytochrome c* 

**150**

**Figure 5.**

electron acceptor substituents [79].

*structure was obtained from protein data Bank, code 1HRC.*

The presence of the iron protoporphyrin IX as the prosthetic group of hemeproteins endows these proteins of electronic and magnetic properties that can be applied in spintronics. The hemeproteins have an additional property that is the folding in chiral structures. [80]. The chiral structures such as the α-helices present in cytochrome *c* (**Figure 5**), for instance, can act as spin filters and respond for the chiral-induced spin selectivity (CISS) effect. To date, cytochrome *c* has been the unique hemeprotein used for spin filtering [28, 33, 38].

New types of spin-dependent electrochemistry measurements have been applied to probe the spin-dependent charge transport properties of nonmagnetic chiral molecules such as cytochrome *c*. Besides cytochrome *c*, the photosystems that are complexes of proteins associated with a non-heme porphyrin, the chlorophyll, also have electron transport capacity with spin selectivity [81, 82]. When the measurements were carried out with different orientations of the PSI protein complex, the dependence of spin polarization with the electron transfer path in photosystem I was proven [81, 82].
