Intramolecular Charge Transfer with 1-tert-Butyl-6-cyano-1,2,3,4-tetrahydroquinoline (NTC6) and Other Aminobenzonitriles. A Comparison of Experimental Vapor Phase Spectra and Crystal Structures with Calculations

Abstract

Calculations of molecular structures in the electronic ground state S(0) and of excited state and fluorescence energies generally refer to the gas phase. This complicates a comparison with experimental data, which often are only available for molecules in solution. Therefore, experimental absorption and fluorescence spectra in the vapor phase are presented for 1-tert-butyl-6-cyano-1,2,3,4-tetrahydroquinoline (NTC6), 1-methyl-6-cyano-1,2,3,4-tetrahydroquinoline (NMC6), 4-(dimethylamino)benzonitrile (DMABN), and 4-(diisopropylamino)benzonitrile (DIABN). NTC6 and DIABN show a dual fluorescence in the gas phase, with emissions from an intramolecular charge transfer (ICT) and a locally excited (LE) state, whereas with NMC6 and DMABN only LE emission is observed. For a comparison of the experimental molecular structure in S(0) with the results of recent computations, X-ray crystal structures of NTC6, NMC6, and several analogues are presented. For DMABN, NMC6, and NTC6, LE/ICT energy diagrams are constructed, in which the experimental energies of the Franck-Condon singlet excited states S(1) and S(2), and the LE and ICT states together with their emissions, are compared with the calculations. The LE and ICT dipole moments are also discussed. This comparison reveals substantial differences, in particular for the ICT energies, but even for the structure of the S(0) ground states. It is concluded that the computed ICT states of NTC6 and DMABN, in which the full conjugation of the phenyl ring is interrupted, is different from the ICT states measured in the experiments.

Red‐Shifted Fluorescent Aminated Derivatives of a Conformationally Locked GFP Chromophore

“…[29] The FQY of tetrahydroquinoline derivative 2 e was the least solvent-dependent among the rigid ABDI-BF2 derivatives synthesized. However, we note that due to the large Stokes shift the LE and ICT bands can be heavily overlapped and hard to separate, like in locked aminobenzonitriles.…”

Intramolecular Charge Transfer Controls Switching Between Room Temperature Phosphorescence and Thermally Activated Delayed Fluorescence

“…Zuschriften D, the dual emission of a-OP was identified as the LE and CT processes in accordance with the PICT model. [11] Thespectra had the profile and dynamic behavior of aC Tb and undergoing at ransient Stokes shift. [12] Since dual emission is very common in the PICT model, a-OP emits blue at % 450 nm and yellow at % 540 nm, which provides ad esign for white light emission from as ingle organic molecule.…”

“…[2c] Since a-OP and OPM are PICT systems, with two singlet states (S 1 and S 2 )that are close in energy,and with different transition characters to enhance ISC,w e propose the PICT model is an ew design strategy for RTP after rigidifying the geometry. [7,11] Figure 4B shows agradual DF decay component of b-OP with av ery sensitive temperature response,t hat is,t his TICT molecule presents efficient TADF with as mall DE(S 1 ,T 1 )o f0 .05 eV (Table S3). Analogously, OMP(a-OMP)a nd b-OMP have similar geometries to b-OP and their efficient TADF properties are seen in Figures 4D and S13.…”

Triple Emission from p‐Dimethylaminobenzonitrile–Cucurbit[8]uril Triggers the Elusive Excimer Emission

“…[1,2] The intramolecular chargetransfer (ICT) state, which gives rise to a red-shifted emission, is favored in polar media, but coexists with the initially populated locally excited (LE) state in nonpolar environments. Experimental investigations involving differently substituted or structurally confined derivatives of DMABN, [13] as well as in media of different polarity and viscosity, [8,9,17] including the gas phase, [10] micelles, [18] solvent clusters, and supramolecular host cavities, [19][20][21] have invariably afforded evidence for the well-known dual emission, with the LE band centered around 350 nm and the ICT band around 450-500 nm. [2][3][4][5][12][13][14][15] Interestingly, excimer emission, which is a competing process for numerous other aromatic chromophores such as anthracene and pyrenes, [16] has not been characterized for DMABN in the solution phase.…”