Design, Synthesis, and Spectral Luminescent Properties of a Novel Polycarbocyanine Series Based on the 2,2‐Difluoro‐1,3,2‐dioxaborine Nucleus

Abstract The natures of the chromophores in symmetric polymethine dyes derived from 2,2‐difluoro‐1,3,2‐dioxaborine have been investigated. Ab initio quantum chemical calculations demonstrated that the presence of dioxaborine end residues stabilizes the frontier levels of the corresponding polymethine dye and makes electron‐density distribution over the oxygen atoms in the chelate ring more even than in the analogous dye structure with boron‐free acyclic end groups. A series of novel symmetric polycarbocyanines and a tricarbocyanine series with variously bridged polymethine chromophores have been synthesized from hitherto unknown pyrimidino‐annelated dioxaborines. The absorption, fluorescence and 13 C NMR spectroscopic data point to the polymethinic type of electron‐density distribution in the 2,2‐difluoro‐1,3,2‐dioxaborine polymethine dye molecules. The fundamental options for controlling the spectral properties of these dyes by modification of their polymethine chains have been evaluated. One of the new compounds synthesized is remarkable among the known open‐chain polymethine dyes for its record high fluorescence quantum yield. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)