Decay times of 4-(dimethylamino)benzonitrile in acetonitrile and conclusions on entropy of activation

Abstract

a b s t r a c tFrom picosecond decay times of 4-(dimethylamino)benzonitrile (DMABN) and 4-(dimethylamino)benzoic acid ethyl ester (DMABE) in acetonitrile (Ref.[1]), a conclusion on entropy effects cannot be made because of large uncertainties of the data. The planarized 1-tert-butyl-6-cyano-1,2,3,4-tetrahydroquinoline (NTC6) as a model for a planar intramolecular charge transfer (ICT) state and the influence of pretwist and size of the amino group is also discussed. For DMABE excited state absorption spectra show a decay of the locally excited (LE) and a rise of the ICT state of 1.0 ps, posing the question whether the lowest excited singlet state is of L b or L a character.

Intramolecular charge transfer of 4-(dimethylamino)benzonitrile probed by time-resolved fluorescence and transient absorption: No evidence for two ICT states and a πσ∗ reaction intermediate

“…22. 57 A similar conclusion is made from the decay of the LE ESA band around 700 nm for MMD in MeCN, see Fig. 7͑a͒.…”

Can the dipolarity of the medium induce the formation of charge transfer structures? An unexpected finding in the photophysics of DMABN

“…Interestingly, Zachariasse et al used their original Scheme 1, which exemplifies the sentence mentioned above, systematically in subsequent papers. 9,[20][21][22][23][24] However, the results of recent work on DMABN 6 seemingly contradict the temperature-dependence assumption and suggest that the absorption behavior of the compound is highly interesting and controversial. Thus, its absorption in acetonitrile at decreasing temperatures from 75 to À45 1C undergoes an unexpected, substantial red shift of 500-600 cm À1 ; 25 also, the absorption in chlorobutane (ClB) exhibits not only a similar shift from 343 to 113 K, but also, seemingly, a new absorption peak in the low energy portion of the first absorption band at very low temperatures (see Fig.…”

On the dual emission of p-dimethylaminobenzonitrile and its photophysical implications

“…15 The currently accepted model for the photophysics of DMABN in the condensed phase is based on the TICT model by Grabowski et al, 11 or slightly modified. However, many contributions to elucidating the viability of these structural models have been experimentally derived from both external [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] and internal factors of the DMABN molecule, [31][32][33][34][35][36][37][38][39][40][41] and theoretical data obtained with the most sophisticated computational methods. [42][43][44][45][46][47][48][49][50][51][52][53][54] Also, this topic has been the subject of several reviews.…”