Near infra-red dyes based on pyrene aza-BODIPYs

Pyrene substituted donor-acceptor type NIR aza-BODIPYs were designed and synthesized. The 1,7-positions of the aza-BODIPY core were substituted by pyrene moieties and the 3,5-positions were substituted with phenyl/2-thienyl or anisyl groups in the aza-BODIPYs. The effect of substituents on their photophysical and electrochemical properties was studied; also, computational studies were carried out for the target aza-BODIPYs. These near infrared dyes displayed the lowest energy absorption maxima in the range of 670-738 nm; whereas, their emission maxima were centered on ≈764 nm. The absorption and emission spectra of the aza-BODIPYs were significantly red shifted (72-94 nm) as compared to the parent tetra-phenylaza-BODIPY. Fluorescence studies suggested effective energy transfer (up to 65%) from donor groups to the aza-BODIPY core in all the compounds. TD-DFT studies indicated significant electronic interactions between energy donor groups and the aza-BODIPY core in all the aza-BODIPYs. The values of HOMO-LUMO gap (ΔE) calculated from cyclic voltammetry data were comparable with those obtained from DFT studies.