A Systematic Series of BODIPY-Cyclotriphosphazene Conjugates: Exploring The Effect of BODIPY Number on Photophysical Properties

Abstract

BODIPY dyes (4,4-difluoro-4-boron-3a,4a-diaza-s-indacene) have attracted increasing interest for their wide range of potential applications. Herein, a series of BODIPY-cyclotriphosphazene conjugates were synthesized via nucleophilic substitution reactions of cyclotriphosphazene with different numbers of distyryl-BODIPY compounds whose conjugation was enhanced by Knoevenagel reaction. Inspired by the enhanced photophysical properties of BODIPY-cyclotriphosphazene compounds reported in the literature compared to single BODIPY, we established a strategy to investigate their photophysical properties systematically. The photophysical properties of novel BODIPY-cyclotriphosphazene conjugates (6-8) were investigated by UV–Vis and fluorescence spectroscopies in different solvents and at different concentrations, and the results were compared within the series. The obtained findings confirm that, under identical analytical conditions, a consistent bathochromic shift in both absorption and fluorescence spectra occurs with an increasing number of BODIPY units attached to the cyclotriphosphazene core. Additionally, the molar absorptivity of novel cyclotriphosphazenes substituted with two, four and six BODIPY moieties was increased by 1.1-, 1.5- and 3.1-fold, respectively, relative to their precursor BODIPY.