Mesophase behaviour of new unconventional shaped azo diester having chloro/nitro derivatives with 1, 2, 4-trisubstituted benzene

[Display omitted] •Unconventional shaped twenty-four mesogenic compounds having (-Cl) Chloro & (- NO2) Nitro derivatives.•Series I exhibits enantiotropic nematic, smectic C as well as smectic A mesophase.•Series II exhibits enantiotropic nematic and smectic A mesophase.•XRD analysis confirms the SmC and SmA. Herein we report the design and synthesis of two new series of mesogenic homologues with unconventional shapes. 3-((4-n-alkoxybenzoyl) oxy)-4-((4-nitrophenyl) diazenyl) phenyl 4-chloro benzoate (In, n = 1 to 8, 10, 12, 14 &16) and 3-((4-n-alkoxybenzoyl) oxy)-4-((4-nitrophenyl) diazenyl) phenyl 4-nitro benzoate (IIn, n = 1 to 8, 10, 12, 14 &16) derivatives were synthesized and characterized by elemental analysis and standard spectroscopic methods. These derivatives contain an azo group at the center along with terminal ester linkage and a lateral alkoxy chain. Two different homologous series of azo diesters containing chloro and nitro groups at the para position were prepared from 4-(p-nitrophenylazo) resorcinol dye. Esterification was done at the phenolic -OH group of the dye by reacting with 4-chlorobenzoic acid to obtain different derivatives for series-In and 4-nirobenzoic acid for series- IIn. The DFT study revealed structural variation in terms of conventional shaped from methoxy to hexadecyloxy derivatives. To monitor phase transition upon heating and cooling, all the compounds were screened under polarizing optical microscope. Mesomorphism was observed for all 24 compounds of series- In and IIn. Enantiotropic nematic mesophase was observed in methoxy to n-hexyloxy derivatives, enantiotropic smectic C mesophase in n-heptyloxy, n-octyloxy and n-decyloxy derivatives, while enantiotropic smectic A mesophase was found in n-decyloxy and other higher analogs of In series. In series IIn, enantiotropic nematic mesophase was observed from methoxy to n-hexyloxy derivatives, while enantiotropic smectic A mesophase was found in n-pentyloxy and higher derivatives. The mesophase behavior of the compounds in both the series was compared with each other and the same geometrical mesogenic structures (Series A-G) to evaluate the effect of relatively polar terminal groups namely, chloro and nitro. Additionally, the effect on the shape of the compounds by changing the alkoxy branch chain on mesophase is also assessed.