Multiply Substituted (Hetero)acenes with a Phosphonate Group at the Central Unit as High-Efficiency Light Emitters.

Abstract

A new variant of the Friedel-Crafts-Bradsher reaction offers access to dialkoxyphosphoryl substituted (hetero)acenes, especially to previously unavailable three- to seven-substituted, tri- and tetracyclic compounds, and features high chemical yields up to 95%, excellent photoluminescence quantum yields (QY) up to 87.7%, large Stokes shifts up to 7943 cm-1 and very mild, room temperature reaction conditions. The (RO)2P(O) has a distinct effect on the photophysical properties of acenes, increasing QYs by more than twofold compared to identical acenes, not substituted by this group. DFT and TD-DFT calculations, combined with electron-hole analysis, indicated that local excitation (LE) had the dominant contribution to the electron excitation mechanism, and charge transfer (CT) of about 30% provided the highest fluorescence quantum yields. Multiply substitution of (hetero)acenes bearing phosphonate moiety and electron-diverse substituents combined with a lower number of fused aromatic rings, appear to be ideal for optimal chemical stability and high photoluminescence. The new, synthetic tool will accelerate exploitation of bulky (hetero)acene emitters for optoelectronic applications.