The synthesis of a novel series of 5,5′-sulfonamide thioindigo derivatives, including a new synthetic methodology (via microwave assisted synthesis), together with a comprehensive electronic spectral and photophysical characterization is described. The study made in solution, as a function of the solvent polarity, showed -rationalized by TDDFT calculations- that in nonpolar solvents the high efficiency of the radiative deactivation channel (50% in dioxane and 70% in benzene) is due to an S₁ (of π,π* origin) in the trans form, whereas in polar solvents the low fluorescence quantum yield (1% or less) is due to the adiabatic stabilization of the trans and saddle S₁ forms, making the sloped type CI (Conical Intersection) with S₀ energetically accessible thus becoming an efficient competitive decay channel to the radiative pathway. It is shown that thioindigo and all the 5,5′-sulfonamide thioindigo derivatives exhibit “on-off” fluorescence that can be tuned by the solvent polarity. The presence of a dark cis form with an S₁ (of n,π* origin) was confirmed by the appearance of a new absorption band, upon irradiation, assigned by TDDFT to an S₂ (of π,π* origin) state.

描述了一系列新的5,5'-磺酰胺硫靛蓝衍生物的合成，包括新的合成方法（通过微波辅助合成），以及全面的电子光谱和光物理表征。在溶液中进行的研究（作为溶剂极性的函数）显示-通过TDDFT计算合理化-在非极性溶剂中，辐射钝化通道的高效率（二恶烷中50％，苯中70％）是由于S ₁（起源于π，π*）反式，而在极性溶剂中，低的荧光量子产率（1％或更少）是由于反式和鞍形S ₁的绝热稳定所致形式，使得可以通过能量途径接近带有S ₀的倾斜类型CI（圆锥形交叉点），从而成为辐射路径的有效竞争衰减通道。结果表明，硫靛蓝和所有5,5'-磺酰胺硫靛蓝衍生物均表现出“开-关”荧光，可通过溶剂极性对其进行调节。通过新的吸收带的出现，证实了具有S ₁（n，π*来源）的暗顺式形式的存在，该吸收带在照射后由TDDFT赋予S ₂（π，π*来源）状态。