Cyclodextrin-Covered Organic Microrods and Microsheets Derived from Supramolecular Self Assembly of 2,4-Dihydroxyazobenzene and 4-Hydroxyazobenzene Inclusion Complexes

Abstract

Abstract The self assembly behavior of 2,4-dihydroxyazobenzene (DHAB) and 4-hydroxyazobenzene (HAB) inclusion complexes were studied by SEM and TEM. Formation of inclusion complexes were characterized by FT-IR, DSC, PXRD, 1H NMR, UV–visible, fluorescence, time-resolved fluorescence, and molecular modeling techniques. Micrometer-sized rods were observed in DHAB:α-cyclodextrin (α-CD) and DHAB:β-cyclodextrin (β-CD) inclusion complexes while microsheets were obtained in HAB/α-CD and HAB/β-CD complexes. In DHAB/CD and HAB/CD individual “barrel” type (head to head arrangement) of 2:2 inclusion complexes form microrods and microsheets through intermolecular hydrogen bonding between the neighboring complexes. Molecular modeling calculations suggest that (i) DHAB and HAB form stable complexes with α-CD and β-CD, (ii) intermolecular hydrogen bonds form between the guests and CDs. Investigations of energetic, thermodynamic, and electronic properties by PM3 method confirmed the stability of the inclusion complex.