The fusion of sufficient-electron heterocycle rings into the[a]/[b]-position of the BODIPY core would result in a large redshift wavelength, thus achieving red or near infrared emission. In this paper, we described the synthesis of nonsymmetric benzo[a]fused and thiophene/ thieno[3,2-b]thiophene[b]fused BODIPY derivatives 2−3 while containing a reactive site, and then, 4−7 were developed by nucleophilic substitution reactions of 3 with various nucleophilic agents in high yields. X-ray crystallographic analysis of 2−7 revealed that the core structure adopted a planar geometry and π−π interactions were observed in the packing structure. BODIPYs 4 and 6−7 displayed a hypochromic shift in the absorption and bathochromic shift in the emission with increasing solvent polarity because of the formation of resonance structures resulting from the change of the C−N distance, which was rationalized by density functional theory (DFT)/time-dependent-DFT calculations.
Non-symmetric thieno[3,2-b]thiophene-fused BODIPYs were designed and characterized, and further functionalization through the Knoevenagel condensation reaction to form a NIR sensor was achieved.
Fusion
selenophene endows the chromophore with more intrinsic and
special functions. Herein, nonsymmetric selenophene-fused BODIPYs
were designed and synthesized starting from the selenophene unit.
The fused ring of selenophene not only maintains the rigid structure
of BODIPY but also further modulates its spectral properties. The
newly prepared dyes possessed many promising properties including
large molar extinction coefficients, low fluorescence quantum yields,
and moderate singlet oxygen generation. Quantum calculations affirmed
that the smaller singlet-triplet energy gap and larger spin–orbit
coupling cause efficient intersystem crossing, thus enhancing the
singlet oxygen generation yield. Furthermore, selenophene-fused BODIPY
exhibited significant phototoxicity with negligible dark cytotoxicity,
based on the fluorescence imaging of the reactive oxygen species detection
experiment.
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