Design of Conjugated Molecules Presenting Short‐Wavelength Luminescence by Utilizing Heavier Atoms of the Same Element Group

The introduction of heavy atoms into conjugated molecules often induces a redshift in the emission spectra. Conversely, we report here a blueshifting effect in the absorption and emission bands of a conjugated organic dye by employing a heavier atom from the same element group. Boron complexes having oxygen‐ and sulfur‐bridged structures in the ligand moiety were synthesized, and their optical properties were compared. Significant optical bands in the absorption and luminescence spectra of the sulfur‐bridged complex were observed in a shorter wavelength region than those of the oxygen‐bridged complex. Theoretical calculations suggest that replacement of the bridging atom by a heavier one should reduce molecular planarity because of the larger atom size. As a result, the degree of electronic conjugation decreases, and this is followed by a blueshift in the optical bands. Finally, a blue‐emissive crystal is demonstrated. Coming up short: The absorption and emission bands of a conjugated organic dye can be blueshifted by employing a heavier atom from the same group in the periodic table. Thus, the spectra of the sulfur‐bridged complex are blueshifted relative to those of the oxygen‐bridged complex. Theoretical calculations suggest that the larger sulfur atom reduces molecular planarity, thus decreasing the electronic conjugation and resulting in the blueshift.