Synthesis and Excited-State Properties of Donor–Acceptor Azahelical Coumarins

Abstract

A set of three donor−acceptor azahelical coumarins (DA-AHCs), namely, H-AHC, Me-AHC, and Ph-AHC, were rationally designed and synthesized, and their excited-state properties were comprehensively investigated. All three DA-AHCs are shown to display very high fluorosolvatochromic shifts as a result of significant intramolecular charge transfer in their excited states. The para-quinoidal forms of the latter apparently contribute predominantly to large dipole moments in their excited states. By virtue of the fact that these helical systems structurally incorporate a highly fluorescent coumarin dye, they exhibit high quantum yields in both solution and solid states. Indeed, their emission behaviors in the crystalline media are shown to be remarkably correlated with their respective crystal packings. Incisive analyses demonstrate (i) strengthening of hydrogen bonding in the excited state promotes quenching (H-AHC), (ii) efficient crystal packing promotes high emission (Me-AHC) by precluding deactivations via vibrational motions, and (iii) loose crystal packing contributes to excited-state deactivation to account for low quantum yields of emission (Ph-AHC).

Coumarin-embedded [5]helicene derivatives: synthesis, X-ray analysis and photoconducting properties

“…One impressive example reported by Moorthy is the fact that azahelical coumarins containing a donor and an acceptor exhibit a high fluorosolvatochromic shift and quantum yield in solution and in the solid state more recently. 14 So far, it remains challenging to incorporate a coumarin unit into nanographene.…”

Organic fluorophore-substituted polyaza-[7]helicenes derived from 1,10-phenanthroline: Studying the chromophoric effect on fluorescence efficiency

“…Push–pull aza-helicenes have been relatively rare in scientific literature; however, they have recently received significant attention owing to the unique combination of improved chirality and the essential properties of delocalized π-electron units prepared with D and/or A units. 13–15 Several research groups have made progress in their synthesis and applied them in various fields, such as dye-sensitized solar cells, 16 circularly polarized luminescence, 17 self-assembly, 18 perovskite solar cells (PSCs), 19–24 and organic light-emitting diodes (OLEDs). 25 To illustrate the most recent achievements in aza-helicenes (Fig.…”

Conjugates of 8-[2,2’-bipyridinyl]coumarins as potential chemosensors for Al3+, Cu2+, Cd2+, Zn2+ ions: synthesis and photophysical properties

“…The coumarin is a promising scaffold for the preparation of a wide range of materials with valuable properties. Although unsubstituted coumarin has low fluorescence in the visible light [1], many properly substituted coumarin derivatives show fluorescence in a wide range [2][3][4][5]. Moreover, coumarins are widely used as fluorescent chemosensors for various analytes, including inorganic anions [6][7][8][9][10][11], metal cations [12][13][14][15][16], reactive oxygen species [17,18], sulfur [19,20] or nitrogen [21][22][23], and biologically active compounds [24,25].…”