Spectroscopic evidence of the presence of an activation barrier in the otherwise barrierless excited state potential energy surface of auramine-O: A femtosecond fluorescence up-conversion study

作者: Shahnawaz Rafiq , Pratik Sen

DOI: 10.1063/1.4821456

关键词: Relaxation (NMR)Excited stateChemistryChemical physicsQuantum yieldPopulationPotential energy surfacePhotochemistryDensity functional theoryTime-dependent density functional theoryGround state

摘要: A widely acclaimed model for the excited state relaxation dynamics of auramine-O involves orientational dimethylanilino moieties along barrierless potential energy surface (PES). Such a would necessitate similar in media offering viscous drag. However, we have noticed an interesting experimental observation showing to ∼8 times larger fluorescence quantum yield chloroform than methanol, though both solvents same viscosity. The femtosecond transients surprisingly depict rise transients, which has not been observed before. This, with simultaneous unexpectedly large lifetime and multi-exponential (in chloroform) questions thoroughly accepted dynamics, as demand short single-exponential decay. Temperature dependent measurements solvent multi-coordinate time-dependent density functional theory calculations further unveil exact nature PES. All these results concomitantly conclude that, at-least chloroform, upon photo-excitation must pass over activation barrier before damping population into ground via sink function through adiabatic coupling electronic states.

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