Absence of dual fluorescence with 4-(dimethylamino) phenylacetylene. A comparison between experimental results and theoretical predictions

Abstract

From ab initio electronic structure calculations it has been predicted that 4-(dimethylamino)phenylacetylene (DACET) will undergo an exothermic intramolecular charge transfer (ICT) reaction with dual fluorescence even under isolated-molecule conditions. Photostationary and time-resolved fluorescence measurements reveal however that an ICT reaction does not occur with DACET under any condition of solvent polarity or temperature studied. DACET is similar to 4-(methyl)aminobenzonitrile, which shows only fluorescence from a locally excited state, but is clearly different from the dual fluorescent 4-(dimethyl)aminobenzonitrile (DMABN). The energy gap A E(S 1,$2) of DACET is larger than that of DMABN, supporting the importance of this gap in these ICT reactions.

Intramolecular Charge Transfer with N,N-Dialkyl-4-(Trifluoromethyl)anilines and 4-(Dimethylamino)benzonitrile in Polar Solvents. Investigation of the Excitation Wavelength Dependence of the Reaction Pathway

“…Due to the larger dipole moment of the S 2 state [17][18][19], the S 1 band more and more disappears with increasing solvent polarity under the S 2 absorption, as seen for DEE (Fig. 1b) and MeCN (Fig.…”

“…1. For DMABN in n-hexane, the weak and structured S 1 band is clearly visible at the low-energy side of the main, more strongly allowed, S 2 absorption [17,18]. Whereas the S 0 → S 1 transition corresponds to the weak S 0 → 1 L b absorption of benzene, the S 2 state has an important charge transfer (CT) admixture to the 1 L a state of benzene origin [19].…”

“…It was assumed that the S 2 state is predominantly prepared during the excitation process, due to the substantially larger transition dipole moment of S 0 → S 2 as compared with S 0 → S 1 [17][18][19]. The possibility to excite the D/A molecule exclusively into S 1 , precluding access to the S 2 /S 1 CI, was not explicitly taken into account.…”

Theoretical Analysis of the Electronic Ground and Excited Franck-Condon State of 2-Alkylamino-(3, 5, or 6)-Methyl-4-Nitropyridine N-oxides

“…on this kind of processes. An interest with molecules, in which donor and acceptor are linked through a single bond or through a bridge of a conjugated double bond, or by the π-electron aromatic system, has also appeared [10][11][12][13][14][15][16][17]. This has given a start to the question on the nature of interactions in intramolecular EDA systems.…”

“…Solving the photophysics of intramolecular EDA systems led to the opening of a large discussion and different models on structure relaxation connected with the intramolecular charge-transfer (ICT) process have been proposed: twisted intramolecular charge transfer (TICT) or planar, wagged, and rehybridized ICT (i.e. PICT, WICT, and RICT) [10,[12][13][14][15][16][17].…”