Molecular aggregation kinetics of Heteropolyene: An Experimental, topological and solvation dynamics studies

Abstract

Herein, we have demonstrated the solvent specific ground state and excited state aggregates of the molecule ((1E,2E)-1,2-bis((E)-3-phenylallylidene)hydrazine: BISCH) in solution. The nature of aggregation at ground state and excited state is different in H2O solvent. The rate of aggregation in water is calculated from steady state absorption and fluorescence spectroscopy respectively. Excited state fluorescence behaviour contributed from aggregates and non-aggregates species have been identified by time resolved fluorescence spectroscopy in H2O. Aggregation is highly sensitive towards solvent polarity and nature of solvent. The effect of solvent on aggregation process has been discussed and explained on the basis of relative change of hydrophobic and hydrophilic interaction of solute-solvents in solution. Further, J-type aggregation of BISCH is also observed in H2O. Further, using 1st order aggregation kinetic model for ground and excited state,) aggregation rate constant has been calculated and found to 8.0x10-4s−1 ((kagg@312 nm) and 1.2x10-4s−1 (kagg@413 nm) respectively. Effect on molecular geometry depending upon Interaction sites of BISCH and solvent molecule is also discussed with the results from DFT calculation. NBO, NCI, DOS, MESP along with various topological analysis are performed for BISCH in water. For BISCH…water molecular system, NBO interaction is observed due to delocalization of lone pair of O35 and N36 to antibonding of H37-O38 and H40-O41, respectively. ELF, LOL, AIM and ALIE calculation are employed to locate the site and magnitude of hydrogen bonding interactions. The AIMD study for BISCH in water shows minimum of the total energy between 125 and 175 fs and 225–275 fs. N…H-O hydrogen bonding interactions such as N36-H40 and N35-H37 varies from 1.8 to 2.6 Å during the molecular dynamics simulation.