Ultrafast Intersystem-Crossing Dynamics and Breakdown of the Kasha-Vavilov's Rule of Naphthalenediimides.
The fluorescence quantum yield of a red naphthalenediimide dye (rNDI) with amino and Br core substituents has been found to decrease by a factor of almost 2 by going from S1 ← S0 to S2 ← S0 excitation. Time-resolved spectroscopic measurements reveal that this deviation from the Kasha-Vavilov's rule is due to an ultrafast, < 200 fs, intersystem-crossing (ISC) from the S2 state to the triplet manifold, due to the ππ* → nπ* character of the transition and to the presence of the heavy Br atom. In non-core substituted naphthalenediimide (pNDI), ISC is slower, ∼2 ps, and was found to be reversible on a time scale shorter than that of vibrational cooling. The fluorescence and triplet quantum yields of rNDI, thus, can be substantially changed by a simple variation of the excitation wavelength.
School of Chemistry and Biochemistry, University of Geneva, 30 Quai Ernest Ansermet, Geneva 4 CH-1211, Switzerland.
Oleksandr
O
Yushchenko
School of Chemistry and Biochemistry, University of Geneva, 30 Quai Ernest Ansermet, Geneva 4 CH-1211, Switzerland.
Giuseppe
G
Licari
School of Chemistry and Biochemistry, University of Geneva, 30 Quai Ernest Ansermet, Geneva 4 CH-1211, Switzerland.
Sandra
S
Mosquera-Vazquez
School of Chemistry and Biochemistry, University of Geneva, 30 Quai Ernest Ansermet, Geneva 4 CH-1211, Switzerland.
Naomi
N
Sakai
School of Chemistry and Biochemistry, University of Geneva, 30 Quai Ernest Ansermet, Geneva 4 CH-1211, Switzerland.
Stefan
S
Matile
School of Chemistry and Biochemistry, University of Geneva, 30 Quai Ernest Ansermet, Geneva 4 CH-1211, Switzerland.
Eric
E
Vauthey
photochemistry; photophysics; spin−orbit coupling; ultrafast spectroscopy