*2.2.7 Inorganic dyes*

*Microwave Heating - Electromagnetic Fields Causing Thermal and Non-Thermal Effects*

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

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)

*2.2.5 Imidazole dyes*

*2.2.6 Thiophene dyes*

emission peak around 443–476 nm [45].

**68**

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 short-circuit photocurrent of 116 μA/cm2 , whereas SnO2 glass/Lu(TBpor)(TBpc)/ PDHEP/TiO2/Al photoelectric cell showed increased short-circuit photocurrent of 691.3 l μA/cm2 under the illumination of white light at 1.201 mW/cm2 [50]. The metal-free phthalocyanine and metallophthalocyanine complexes (**67** and **68a-c**) of Cu+ , Cu2+, Co2+, Ni2+, Fe2+, Zn2+, Pd2+, Pt4+, and Ru3+ was prepared by the reaction of corresponding azo dyes with metal salts using microwave heating, which were obtained in poor yields by conventional heating [51].
