Radiationless Deactivation Process of 1-Dimethylamino-9-fluorenone Induced by Conformational Relaxation in the Excited State: A New Model Molecule for the TICT Process

Abstract

The deactivation process of excited 1-(dimethylamino)-9-fluorenone (1-DMAF) was investigated by means of steady-state and time-resolved fluorescence spectroscopy. Fluorescence decay profiles for 1-DMAF, which has a relatively short lifetime (several tens of picoseconds in low viscosity solvents at ambient temperature) are much affected by the fluidity of the surrounding solvent. The lifetimes increase in glassy solvents at 77 K as well as with increasing viscosity. These results indicate that conformational relaxation by the dimethylamino group plays an important role in the deactivation process of 1-DMAF. Detailed analysis of the temperature dependence of the fluorescence lifetime revealed that the conformational relaxation process has a very small intramolecular activation barrier (5.4 kJ/mol). Results of MO calculations suggest that the dimethylamino moiety of 1-DMAF is pretwisted in the ground state and that the most stable structure in the excited state is a twisted intramolecular charge transfer (TICT) state. 1-DMAF could be a new model molecule that exhibits the TICT phenomena.

A Remarkable Ligand Orientational Effect in Osmium‐Atom‐Induced Blue Phosphorescence

“…These results indicate that the large amplitude motions [21] do not trigger the radiationless deactivation in 2. Both the intensity and the relaxation dynamics of the phosphorescence of 2 also revealed a strong temperature dependence; the lifetime increased from 88.7 ns at 298 K to 6.9 ms at 77 K. Interestingly, although the spectral features for 1 and 2 are similar in solution, they are notably different in the single crystal; the emission of 1 is broader and red-shifted compared with that of 2 (see Figure 3 for comparison).…”

Reactivity of 2,1‐Benzisoxazole in Palladium‐Catalyzed Direct Arylation with Aryl Bromides

“…This method gives ao ne-step access to 1-amino-9H-fluoren-9-ones, which exhibit important physical properties. [11] The discoveryo fe fficient methods for the synthesis of 2-aminobenzophenonesi nalimited number of steps is also an important research field in organic synthesis. Therefore, the scope of the benzoisoxazole ring-opening reactionf or access to 2-aminobenzophenones under classicalc onditions was in- www.chemcatchem.org vestigated (Scheme 6).…”

Ultrafast Relaxation Dynamics of the Excited States of 1‐Amino‐ and 1‐(N,N‐Dimethylamino)‐fluoren‐9‐ones

“…[15,16,22,24,26,27] In spite of this, we wish to bring out some important aspects of these properties, which will be useful for the present discussion on the dynamics of the excited states. In addition, some important properties of the excited states of these molecules have not been the subject of discussion in the earlier publications.…”

“…While both compounds are weakly fluorescent in all kinds of solvents, the fluorescence quantum yield for 1DMAF is about two orders of magnitude less than that for 1AF. [22,26,27] In aprotic solvents, the absorption and fluorescence maxima for both 1AF and 1DMAF show bathochromic shifts (i.e. the maximum of the band shifts towards lower energy) as the dielectric polarity of the solvent [measured by the dielectric polarity function F, as defined in Eq.…”

“…[27] Accepting the theoretically calculated value of the dipole moment of the S 0 state of 1DMAF be 3.6 D, the dipole moment of the S 1 (LE) state is 7.1 D. This value agrees well with the value of 6 D that has been theoretically obtained for the same state having the conformational geometry with the dimethylamino group pretwisted with respect to the fluorenone plane. [26] …”