Hoche Joscha, Schulz Alexander, Dietrich Lysanne Monika, Humeniuk Alexander, Stolte Matthias, Schmidt David, Brixner Tobias, Würthner Frank, Mitric Roland
Institut für Physikalische und Theoretische Chemie , Universität Würzburg , Am Hubland , 97074 Würzburg , Germany . Email:
Institut für Organische Chemie , Universität Würzburg , Am Hubland , 97074 Würzburg , Germany . Email:
Chem Sci. 2019 Dec 4;10(48):11013-11022. doi: 10.1039/c9sc05012d. eCollection 2019 Dec 28.
Fluorophores with high quantum yields are desired for a variety of applications. Optimization of promising chromophores requires an understanding of the non-radiative decay channels that compete with the emission of photons. We synthesized a new derivative of the famous laser dye 4-dicyanomethylen-2-methyl-6--dimethylaminostyryl-4-pyran (), , merocyanine 4-(dicyanomethylene)-2--butyl-6-[3-(3-butyl-benzothiazol-2-ylidene)1-propenyl]-4-pyran (). We measured fluorescence lifetimes and quantum yields in a variety of solvents and found a trend opposite to the energy gap law. This motivated a theoretical investigation into the possible non-radiative decay channels. We propose that a barrier to a conical intersection exists that is very sensitive to the solvent polarity. The conical intersection is characterized by a twisted geometry which allows a subsequent photoisomerization. Transient absorption measurements confirmed the formation of a photoisomer in unpolar solvents, while the measurements of fluorescence quantum yields at low temperature demonstrated the existence of an activation energy barrier.
各种应用都需要具有高量子产率的荧光团。对有前景的发色团进行优化需要了解与光子发射相竞争的非辐射衰变通道。我们合成了著名激光染料4-二氰基亚甲基-2-甲基-6-二甲基氨基苯乙烯基-4-吡喃（）、部花青4-（二氰基亚甲基）-2-丁基-6-[3-（3-丁基-苯并噻唑-2-亚基）-1-丙烯基]-4-吡喃（）的一种新衍生物。我们在多种溶剂中测量了荧光寿命和量子产率，发现了与能隙定律相反的趋势。这激发了对可能的非辐射衰变通道的理论研究。我们提出存在一个对溶剂极性非常敏感的锥形交叉点势垒。锥形交叉点的特征是扭曲的几何结构，这允许随后的光异构化。瞬态吸收测量证实了在非极性溶剂中形成了光异构体，而低温下荧光量子产率的测量证明了活化能垒的存在。
