Two-Photon Absorption Response of Functionalized BODIPY Dyes in Near-IR Region by Tuning Conjugation Length and Meso-Substituents

BODIPY dyes substituted by phenol or -COOMe unitsat themeso-position (C8) with and without a distyryl group including a methoxymoiety at the -C3 and -C5 positions of the BODIPY have been synthesizedto analyze the photophysical properties. To clarify the ground-stateinteraction, absorption and emission features were investigated inthe THF environment. Extending the & pi;-conjugation with the methoxymoiety at -C3 and -C5 positions of BODIPY leads to a spectral shiftingof the absorption maxima toward red by 120 nm. In addition, attachingthe -COOMe unit at the meso-position of the BODIPY structureincreases nonradiative molecular relaxation as compared to compoundspossessing phenol substituents at the same position. We have investigatedthe effect of phenol and a -COOMe group and & pi;-extendedconjugation length with a methoxy moiety on the properties of two-photonabsorption (TPA) and electron transfer dynamics by performing open-aperture(OA) Z-scan and femtosecond transient absorption spectroscopy measurements,respectively. The synthesized BODIPY compounds with the distyryl groupincluding the methoxy unit show TPA character due to the longer conjugationlength and therefore intramolecular charge transfer ability. Basedon the OA Z-scan experiments upon photoexcitation with 800 nm pulsedlaser light, TPA cross-section values were obtained as 74 and 81 GMfor the compounds possessing phenol and -COOMe units at themeso-position of BODIPY treated by distyryl group with methoxy moieties,respectively. Additionally, optical and electronic properties werecalculated theoretically by using the DFT method.

Automated summary

In this study, BODIPY dyes substituted by phenol or -COOMe units at the meso-position were synthesized and their photophysical properties were analyzed. It was observed that the introduction of a methoxy moiety at the -C3 and -C5 positions of BODIPY caused a red shift in absorption maxima. Additionally, attaching a -COOMe unit at the meso-position increased nonradiative molecular relaxation compared to compounds with phenol substituents. The effect of phenol and -COOMe groups and extended π-conjugation with a methoxy moiety on two-photon absorption and electron transfer dynamics was investigated using open-aperture (OA) Z-scan and femtosecond transient absorption spectroscopy measurements.