*2.2.4 Benzimidazole dyes*

Benzimidazole dyes are known to exhibit photophysical, photovoltaic, and optical properties [39]. An approach has been made to synthesize benzimidazoquinolines **55a-c**, substituted with piperidine, pyrrolidine, and piperazine moieties by uncatalyzed amination protocol under microwave heating in relatively high yields (56–90%), which by conventional heating after several days gave **55a-c** only in low yields (<10%). The emission spectra of **55a-c** showed an increase in the fluorescence intensity when interacted with the calf thymus DNA (*ct*-DNA) [40]. The microwave promoted synthesis of bisbenzimidazolyl derivatives upon *N*-alkylation gave water-soluble fluorescent dyes **56a-b**. These dyes proved to be highly selective fluorescent probe toward Zn2+ in aqueous solution and the mixture of dye-Zn2+ could detect picric acid by fluorescence quenching [41]. Under solvent-free microwave irradiation, a series of 2-substituted styryl benzimidazole dyes **57a-g** and **58a-f** were prepared by the condensation of 2-alkyl benzimidazoles with aromatic aldehydes in the presence of acetic anhydride [42].

#### *2.2.5 Imidazole dyes*

The imidazole moiety is immensely employed in DSSC's [43]. Interestingly these dyes **59a**-**d**, **60**, and **61** are prepared by one-pot condensation of α-diketone (benzil), aryl aldehydes, and ammonium acetate in the presence of glacial acetic acid under microwave irradiation. Furthermore, the dyes **59a**-**d** have been proved to be potential antimicrobial agents against *E. coli*, *B. subtilis*, *S. aureus,* and *L. monocytogenes* [44]. The dye **60** exhibited a strong two-photon upconverted blue fluorescent emission peak around 443–476 nm [45].

#### *2.2.6 Thiophene dyes*

Thiophene oligomers and polymers have put forward extensive applications in organic electronics, owing to their remarkable performance as organic semiconductors [46]. A series of thiophene oligomer based fluorophores appended with 4-sulfo-2,3,5,6-tetraflurophenyl ester **62a**, *N*-hydroxysuccinimidyl ester **62b**, and phthalimide **63a-b** are prepared efficiently in shorter reaction times by sequential Pd(II) catalyzed Suzuki cross coupling reaction by taking advantage of microwave irradiation. The dyes **62a-b** were evaluated for their labeling toward monoclonal antibodies Anti-CD38. The dye **62a** showed a larger bathochromic shift compared to **62b** and exhibited greater affinity toward the monoclonal antibody [47]. The cyclic voltammetry, UV–visible spectroscopy, and X-ray crystallographic studies of the dyes **63a** and **63b** revealed π-π stacking packing mode which led to increased charge carrier mobility envisaging as an ambipolar semiconductor with applications in both Organic Thin-Film transistors (OTFT) and Organic-light Emitting Transistors (OLET) [46, 48]. A one-pot three-component synthetic route was used to prepare thiophene-coumarin based dyes **64a-j** in 92–96% yields from hours to min by the use of microwave irradiation technique from 3-acetyl coumarin, malononitrile, and elemental sulphur (S8). The spectroscopic data of the dyes **64a-j** showed a bathochromic shift in various solvents. The dye **64g** was further investigated for its pH sensitivity *via* deprotonation and reverse protonation in two solvent systems (DMSO and DMSO/H2O binary mixture) using absorption and fluorescence techniques. The -OH group of **64g** is susceptible to deprotonation under alkaline medium (TBAOH, tetrabutylammonium hydroxide)

**69**

*Microwave Synthesized Functional Dyes DOI: http://dx.doi.org/10.5772/intechopen.94946*

*2.2.7 Inorganic dyes*

691.3 l μA/cm2

**2.3 Photochromatic dyes**

Cu+

short-circuit photocurrent of 116 μA/cm2

obtained in poor yields by conventional heating [51].

observed with the incremental addition of TFA [49].

and reverse protonation by the addition of trifluoroacetic acid (TFA). A distinct fluorescence color change from light blue to green was observed with the incremental addition of TBAOH to the solution of **64g** and reverse phenomena was

Inorganic dyes are procured when the organic dyes are combined with appropriate metals. Typically monoazodyes containing additional groups such as amino, hydroxyl, and carboxyl groups which are capable of forming coordination complexes with metal ions are used. This organo-metallic combination could lead to enhanced optical properties. The synthesis of organo soluble 4-*t*-butylphthalocyanine (TBPc) and organo soluble sodium salt of sulfonated phthalocyanine (Pc-SO3Na) metal complexes of Cu2+, Mg2+, and Zn2+ (**65a-b**) has been reported. Further, lutetium complex [Lu(TBPor)(TBPc)] **66** ligated with 4-*t*-butylporphyrin (TBpor) and 4-*t*-butylphthalocyanine (TBPc) rings were obtained *via* the reaction of lutetium acetate (LuOAc) with corresponding ligands under microwave irradiation. The prepared complexes were blended with *N*,*N*′-bis-(1,5-dimethylhexyl)-3,4:9,10 perylene-bis-(dicarboximide) [PDHEP] and SnO2 glass to fabricate photoelectric cells. The SnO2 glass/Mg-Pc(SO3Na)4/PDHEP/Al photoelectric cell exhibited a

PDHEP/TiO2/Al photoelectric cell showed increased short-circuit photocurrent of

under the illumination of white light at 1.201 mW/cm2

metal-free phthalocyanine and metallophthalocyanine complexes (**67** and **68a-c**) of

Some materials at their molecular level exhibit a property of changing their absorption spectra on exposure to light radiation. This is usually a reversible change and is accompanied with alteration in the physical or chemical property. This kind

corresponding azo dyes with metal salts using microwave heating, which were

, Cu2+, Co2+, Ni2+, Fe2+, Zn2+, Pd2+, Pt4+, and Ru3+ was prepared by the reaction of

, whereas SnO2 glass/Lu(TBpor)(TBpc)/

[50]. The

and reverse protonation by the addition of trifluoroacetic acid (TFA). A distinct fluorescence color change from light blue to green was observed with the incremental addition of TBAOH to the solution of **64g** and reverse phenomena was observed with the incremental addition of TFA [49].
