Two-Step Mechanochromic Luminescence of N,N′-Bis-Boc-3,3′-di(pyren-1-yl)-2,2′-biindole

Despite recent advances in the development of mechanochromic luminescent organic molecules, the mechano‐responsive properties of intramolecularly stacked fluorophores are not well documented. Herein, the synthesis and emission properties of three N,N′‐bis‐Boc‐3,3′‐diaryl‐2,2′‐biindole (Boc=tert‐butoxycarbonyl) derivatives as a new class of solid‐state emissive fluorophores are described. For a 3,3′‐dipyrenyl derivative in the crystalline state, partial intramolecular stacking of the dipyrenyl groups was observed, which results in a two‐step mechanochromic luminescence from blue (λem=462 nm) to green (λem=516 nm) and yellow (λem=535 nm). Three hue: The synthesis and emission properties of three N,N′‐bis‐Boc‐3,3′‐diaryl‐2,2′‐biindole (Boc=tert‐butoxycarbonyl) derivatives as a new class of solid‐state emissive fluorophores are described. For a 3,3′‐dipyrenyl derivative in the crystalline state, partial intramolecular stacking of the dipyrenyl groups was observed, which results in a two‐step mechanochromic luminescence from blue (λem=462 nm) to green (λem=516 nm) and yellow (λem=535 nm; see figure).