Spectral tuning of 11-cis retinal in conjugation with Au14 cluster and concomitant effect on isomerization: A theoretical outlook

Abstract

The present study explores the optical properties of retinal molecules in presence of small gold cluster (Au14), where the cluster motifs are varied through Oh, D2h and C4v symmetries. The constructive interference of the transition dipole moments (TDMs) in retinal-gold nanoconjugates is responsible for most intense electronic transitions. The charge transfer transition from the occupied Au cluster orbital to the unoccupied retinal orbital is playing significant role in the spectral shift of the conjugates. The vibrational frequency analysis of 11-cis retinal and its conjugate (Au14 in D2h symmetry) reveal that the different vibrational modes associated with the isomerization process are red shifted in the conjugate. The conjugation of isolated retinal with gold probes makes the process of 11-cis to all-trans isomerization thermodynamically favorable. The entire evaluation reflects the effect of gold cluster in the spectral tuning of retinal molecules and reveals its relevant consequences on photoisomerization and hence the process of vision.

Keywords

• Photoisomerization
• Gold cluster
• Nano-bio conjugate
• DFT
• Retinal