Negligible shift of potential in longer-chain carotenoids as revealed by a single persistent peak of stimulated emission followed by transient-absorption

Upon excitation of lycopene, anhydrorhodovibrin or spirilloxanthin to the 1B u + ( 0 ) state, stimulated emission followed by transient-absorption was observed as a single peak with the 3A g - ( 0 ) energy that had been determined by measurement of resonance-Raman excitation profiles. This observation was explained in terms of negligible shift of the 3A g - potential, in reference to the 1A g - potential, where only the 3A g - ( υ ) → 1A g - ( υ ) emission and the 3A g - ( υ ) ← 1A g - ( υ ) absorption become allowed during the vibrational relaxation of υ = 2 → 1 → 0, starting from the 3A g - ( 2 ) level generated by diabatic internal conversion from the 1B u + ( 0 ) level, in anhydrorhodovibrin, for example.