8‐Amido‐BODIPYs: Synthesis, Structure and Optical Properties Illustrating Amine to Amide, Blue to Green Emission

LI Saucedo, RI Roacho, P Tu… - …, 2020 - Wiley Online Library
ChemistrySelect, 2020Wiley Online Library
Abstract Treatment of 8‐NH2‐BODIPY, 1 a,(BODIPY= boron, difluoro [2‐[(2H‐pyrrol‐2‐
ylidene‐κN) methyl]‐1H‐pyrrolato‐κN]‐) with NaH, followed by addition of acylchlorides, R.‐
C (= O) Cl, R= CH3, CH2Cl, Ph, produces the corresponding 8‐amido‐BODIPYs, RC (= O)
NH‐BODIPYs in good yield, R= Me, 2 (62%); ClCH2, 3 (52%); Ph, 4 (74%). Structural and
spectroscopic analyses indicate a lack of N‐lone pair delocalization to the BODIPY core
(normally exhibited by the parent 8‐amino‐BODIPYs) as a result of the BODIPY‐NH+= CR …
Abstract
Treatment of 8‐NH2‐BODIPY, 1a, (BODIPY=boron, difluoro[2‐[(2H‐pyrrol‐2‐ylidene‐κN)methyl]‐1H‐pyrrolato‐κN]‐) with NaH, followed by addition of acylchlorides, R.‐C(=O)Cl, R=CH3, CH2Cl, Ph, produces the corresponding 8‐amido‐BODIPYs, RC(=O)NH‐BODIPYs in good yield, R=Me, 2 (62 %); ClCH2, 3 (52 %); Ph, 4 (74 %). Structural and spectroscopic analyses indicate a lack of N‐lone pair delocalization to the BODIPY core (normally exhibited by the parent 8‐amino‐BODIPYs) as a result of the BODIPY‐NH+=CR‐O contribution to the amide structure. The new materials 2, 3, and 4 exhibit C8‐N bond lengths significantly longer than the those in related 8‐amino‐BODIPYs, average 1.407 Å vs 1.327 Å; and the N‐Cacyl bond lengths in the region associated with regular amides, average 1.38 Å. This lack of 8‐N‐BODIPY pi interaction results in a significant bathochromic shift in the absorbance spectra (modelled by empirically corrected Time Dependent‐Density Functional Theory (TD‐DFT) calculations) and removes the well‐established blue emission for 8‐amino‐BODIPYs and the new materials revert to the “normal” green emission generally noted for 8‐substituted‐BODIPYs.
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