Supporting Information

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1 Supporting Information A Counterintuitive Absence of an Excited-State Intramolecular Charge Transfer Reaction with 2,4,6-Tricyanoanilines. Experimental and Computational Results Klaas A. ZACHARIASSE,*,a Sergey I. DRUZHININ,*,a Victor A. GALIEVSKY, a Sergey KOVALENKO,*,b Tamara A. SENYUSHKINA, a Peter MAYER, c Mathias NOLTEMEYER, d Martial BOGGIO-PASQUA,*,e Michael A. ROBB* ;f a Max-Planck-Institut für biophysikalische Chemie, Spektroskopie und Photochemische Kinetik, Göttingen, Germany b Institut für Chemie, Humboldt Universität zu Berlin, Brook-Taylor Strasse 2, Berlin, Germany c Department Chemie und Biochemie, Ludwig-Maximilians-Universität, Butenandtstrasse 5-13, Haus F, München, Germany d Institut für Organische Chemie, Universität Göttingen, Tammannstrasse 2, Göttingen, Germany e Laboratoire de Chimie et Physique Quantiques, UMR 5626, IRSAMC, CNRS and Université Toulouse 3, 118 route de Narbonne, Toulouse, France f Chemistry Department, Imperial College, London, SW7 2AZ, UK kzachar@gwdg.de; Fax:

2 Figure S1. Absorption spectra at 25 o C of 2,4,6-tricyano-N,N-dimethylaniline (TCDMA) in (a) n-hexane, (b) diethyl ether (DEE), (c) acetonitrile (MeCN) and of 2,4,6-tricyanoaniline (TCA) in (d) MeCN. 2

3 Figure S2. Absorption spectra at 25 o C of 2,4,6-tricyano-N-methylaniline (TCMA) in (a) cyclopentane (CP), (b) diethyl ether (DEE), and (c) acetonitrile (MeCN). 3

4 Figure S3. Single exponential fluorescence decays in acetonitrile (MeCN) at 25 o C. (a) 2,4,6-tricyano-N,Ndimethylaniline (TCDMA) at 448 nm (Figure 2c), (b) 2,4,6-tricyano-N-methylaniline (TCMA) at 400 nm (Figure 3c) and (c) 2,4,6-tricyanoaniline (TCA) at 390 nm (Figure 3f), measured at the fluorescence maxima. The decay time τ with the corresponding amplitude A, see eq 7, is given in the figure. The weighted deviations sigma, the autocorrelation functions A-C and the values for χ 2 are also indicated. Excitation wavelength: (a) 279 nm, (b) 298 nm, (c) 272 nm. Time resolution: ps/channel (a and c) and ps/channel (b), with a time window of 1400 effective channels. See the caption of Figure 8. 4

5 Transient Absorption and ESA Spectra of TCDMA in MeCN. In Figure S4a, the transient absorption spectra of TCDMA in MeCN at 356 nm excitation (pump and probe parallel) are presented and the ESA spectra are depicted in (b), after correction for the BL and SE spectra. The SE spectra show a time-dependent red-shift (Figure 13b), with λ max (t = 0) = nm and λ max (t = ) = nm. λ max (SE) shifts from 428 nm at t = 80 fs to 455 nm at t = 2.6 ps. The λ max (ESA) peak at 604 nm at a delay of 80 fs undergoes a blue-shift to 578 nm at 2.6 ps delay (Figure S4b, horizontal arrow). At this delay time, the ESA spectrum has other maxima at 518 and 360 nm (minor) as well as a main peak at 310 nm. This last absorption band does practically not change with time. From the fitting of the spectral blue-shift of the ESA band around 600 nm with eq 8 (Figure S4c) the Gaussian solvation time ω -1 = 68 fs and the diffusional solvation time τ s = 610 fs are determined, the same times (60 and 610 fs) as found with TCA (Figure 11c). The band integral BI(535,690) decays as a single exponential with a time τ of 2.1 ps (Figure S4d). This decay represents the disappearance of the absorption maximum around 600 nm. Simultaneously, the BI(450,530) shows a growing-in with the same decay time. In Figure S4b, an indication of an isosbestic point appears around 520 nm, which would indicate that (at least, ref 52) two dynamically interconnected excited states are present for TCDMA in MeCN, see Figure 13b. 5

6 Figure S4. 2,4,6-Tricyano-N,N-dimethylaniline (TCDMA) in acetonitrile (MeCN) at 356 nm excitation (pump and probe parallel). (a) Transient absorption spectra and (b) excited-state absorption (ESA) spectra, at pumpprobe delay times between 0.08 and 2.6 ps, after subtraction of the bleach (BL) spectrum and stimulated emission (SE). The BL and SE spectra are also depicted (for fluorescence spectrum, see Figure 2c). The BL maxima are at 310 and 373 nm.the maximum of the SE emission band shifts from 428 nm at time zero (t = 0) to 455 nm at time infinity (t = ), see text. (c) The blue-shift of the maximum of the ESA band around 590 nm (from 604 to 578 nm, in (b)) is fitted by using eq 8, with the Gaussian solvation time ω -1 = 68 fs and the diffusional solvation time τ s = 610 fs. (d). The band integral BI(535,690) has a decay time τ 1 of 2.1 ps, whereas BI(450,530) grows in with the same time. The amplitude A 1 and the large offset A 0 are also presented (eq 9). See the caption of Figure 11. max ~ν ( ) = cm -1 (576.6 nm). 6

7 On the Meaning of Locally Exited (LE). (references numbered as in the main paper). When searching in Google for the expression locally excited (LE), one finds that LE is predominantly used for states of D/A molecules from which the normal emission is emitted, which is the initially excited S 1 state. This apparently is the normal usage of the term LE, conform with its use in the present paper. The first paper that appears in the Google search, is one on excimer formation, in which process the excitation is first localized on the excited state monomer M* (LE state), from which the excimer is formed upon collision of M* with M, the excitation now becoming delocalized in the excimer (MM)*. As mentioned in the main paper, the term LE originated from intermolecular exciplex formation studies, in which the excitation is initially localized on the monomer 1 A*. We did not establish when the term LE appeared in theoretical studies, probably after its introduction in the experimental literature. This does not mean that the term LE is without problems, as has been pointed out previously (refs 17,45,54,55). In ref 45, footnote 14: The use of the name LE state in the ICT reaction of D/A-substituted molecules such as DMABN obviously originates from the formal kinetic similarity of the ICT reaction scheme consisting of an initially excited LE state and an ICT state and the schemes applicable to excimer and exciplex formation. In ref 54, footnote 7 and ref 55, footnote 6:.Strictly speaking, the excitation is just as delocalized in the LE state as in the ICT state of molecules such as DMABN, the difference mainly residing in the degree of charge separation. When this formal kinetic analogy as the basis for the term LE is considered to be unacceptable, then it may be best to use the neutral term S 1 state. In conclusion, we generally have followed the normal usage of LE, although it was clear that such an LE state can have a substantial dipole moment. This was experimentally established at an early stage of the ICT investigations (see ref 56). Also in the case where an ICT (i.e., LE ICT) reaction does not occur, such as with 4-aminobenzonitrile (MABN) and aminobenzonitrile (ABN), the fluorescing S 1 state is called LE, irrespective of its large dipole moment of around 9 D. Clearly, the term LE is used without considering the molecular nature of the emitting state. That is also the declared definition of LE in the experimental part of the present paper. In other words, we stick to the usual meaning of LE, although we are aware of the semantic problems involved. In the theoretical description resulting from the computations on TCDMA and TCA, a different and possibly even more difficult situation is encountered. Here, by adopting a VB description, the possibility exists to define LE and ICT in terms of orbital transitions. 7

8 Although such a definition of LE may be straightforward in the case of alternating aromatic hydrocarbons such as naphthalene and benzene, it is more complicated with anilines and a fortiori with aminobenzonitriles. In the present paper the choice has been made to associate LE with the orbital transition HOMO to LUMO+1, whereas for ICT the transition HOMO LUMO was taken. In fact, the situation is more complex, when one addresses the real excited state situation in TCDMA and TCA, due to the extensive state mixing, as outlined in the paper. That the choice of a particular orbital transition for LE is not always straightforward and without possible ambiguity, can be seen from the different orbital definition for LE (HOMO to LUMO+1) adopted in the case of the related dicyanoanilines (refs 23,25,26), as mentioned in the paper. This complicated situation has led us to include in the paper a section specifically addressing these difficulties: Different Definitions for LE and ICT in Experiments and Calculations. 8

9 θ = 38, 36 β = 7.9, 8.2 ϕ = 0, 0 μ = 3.2 D, 3.5 D Figure S5. Ground state optimized geometry of TCDMA at the RASSCF(20,7+5+7)[2,2] and CASSCF(6,5) levels. Bond lengths are in pm. Angles θ and ϕ are defined in Figure 1. Angle β equals 180 o (C(4)C(3)C(2)C(9)), see Figure 1. μ is the S 0 dipole moment. RASSCF values in normal font, CASSCF data in italics. 9

10 B (Platt s Figure S6. (a) Main electron configurations in the first three singlet states of benzene from CASSCF(6,6)/6-31G* calculation: ground state 1 A 1g, covalent first excited state 1 BB2u (Platt s 1 1 L b state), and ionic second excited state B 1 1u L a state), (b) Main electron configurations of the LE state of TCDMA. One can see that the configurations correspond to the ones of the 1 BB2u state of benzene. Note that it is the plus combination in the LE state of TCDMA instead of the minus in the first excited state of benzene, but the phase of the singly populated π* orbitals in the second configuration is opposite, therefore the two states correlate. 10

11 Figure S7. Main electron configurations of the ICT states of TCDMA: (a) ICT-Q state at S 0 geometry, (b) ICT-Q state at its optimized geometry, (c) ICT-AQ state at S 0 geometry, (d) ICT-AQ state at its optimized geometry. 11

12 Figure S8. Computed absorption spectra of TCDMA using time-dependent density functional theory (TD-DFT) (a) in the gas phase using the 6-31G* basis set, (b) in acetonitrile using the Polarizable Continuum Model and the aug-cc-pvtz basis set. In case (a), the calculation was performed over the lowest three excited states considered in this theoretical study (ICT-AQ, ICT-Q and LE). The position of the peaks are in good agreement with the CASPT2 values of 375 nm, 279 nm, and 234 nm for the vertical transitions S 0 ICT-AQ, S 0 ICT-Q, and S 0 LE, respectively (obtained from Table 9). In case (b), the calculation was performed over the lowest twenty singlet states and allows comparison with the experimental spectra in Figures 2c and S1c. 12

13 Figure S9. (a) Structure of the conical intersection between the ICT-Q and ICT-AQ states of TCDMA optimized with CASSCF(6,5)/6-31G*. Bond lengths are in pm. (b) Topology of the adiabatic S 1 potential energy surface around the conical intersection represented in the space of the two degeneracy-lifting coordinates. 13

14 Figure S10. Main electron configurations in the wavefunction of the S 1 (LE,ICT-AQ) state of TCA. One can see that the configurations correspond to the ones in the LE state of TCDMA (see Figure S6b), but the promoted electron in the main configuration (c 2 ) is excited from an orbital with a strong amino lone pair character, giving rise to the mixing with the ICT-AQ state. 14

15 TABLE S1: RASSCF/6-31G* Optimized Cartesian Coordinates and Absolute CASSCF/cc-pVDZ and CASPT2/cc-pVDZ Energies for TCDMA Ground state minimum E CASSCF (S 0 ) = a.u. E CASSCF (ICT-Q) = a.u. E CASSCF (ICT-AQ) = a.u. E CASSCF (LE) = a.u. E CASPT2 (S 0 )= a.u. E CASPT2 (ICT-Q) = a.u. E CASPT2 (ICT-AQ) = a.u. E CASPT2 (LE) = a.u. N N N N C C C C C C C C C C C H H H H H H H H

16 ICT-Q state minimum E CASSCF (S 0 ) = a.u. E CASSCF (ICT-Q) = a.u. E CASSCF (ICT-AQ) = a.u. E CASSCF (LE) = a.u. E CASPT2 (S 0 ) = a.u. E CASPT2 (ICT-Q) = a.u. E CASPT2 (ICT-AQ) = a.u. E CASPT2 (LE) = a.u. N N N N C C C C C C C C C C C H H H H H H H H

17 ICT-AQ state minimum E CASSCF (S 0 ) = a.u. E CASSCF (ICT-Q) = a.u. E CASSCF (ICT-AQ) = a.u. E CASSCF (LE) = a.u. E CASPT2 (S 0 ) = a.u. E CASPT2 (ICT-Q) = a.u. E CASPT2 (ICT-AQ) = a.u. E CASPT2 (LE) = a.u. N N N N C C C C C C C C C C C H H H H H H H H

18 LE state minimum E CASSCF (S 0 ) = a.u. E CASSCF (ICT-Q) = a.u. E CASSCF (ICT-AQ) = a.u. E CASSCF (LE) = a.u. E CASPT2 (S 0 ) = a.u. E CASPT2 (ICT-Q) = a.u. E CASPT2 (ICT-AQ) = a.u. E CASPT2 (LE) = a.u. N N N N C C C C C C C C C C C H H H H H H H H

19 TABLE S2: RASSCF/6-31G* Optimized Cartesian Coordinates and Absolute CASSCF/cc-pVDZ and CASPT2/cc-pVDZ Energies for TCA Ground state minimum E CASSCF (S 0 ) = a.u. E CASSCF (LE,ICT-AQ) = a.u. E CASSCF (ICT-Q) = a.u. E CASPT2 (S 0 ) = a.u. E CASPT2 (LE,ICT-AQ) = a.u. E CASPT2 (ICT-Q) = a.u. N N N N C C C C C C C C C H H H H

20 LE,ICT-AQ state minimum E CASSCF (S 0 ) = a.u. E CASSCF (LE,ICT-AQ) = a.u. E CASSCF (ICT-Q) = a.u. E CASPT2 (S 0 ) = a.u. E CASPT2 (LE,ICT-AQ) = a.u. E CASPT2 (ICT-Q) = a.u. N N N N C C C C C C C C C H H H H

21 ICT-Q state minimum E CASSCF (S 0 ) = a.u. E CASSCF (LE,ICT-AQ) = a.u. E CASSCF (ICT-Q) = a.u. E CASPT2 (S 0 ) = a.u. E CASPT2 (LE,ICT-AQ) = a.u. E CASPT2 (ICT-Q) = a.u. N N N N C C C C C C C C C H H H H

22 TABLE S3: Selected Angles and Dipole Moments of the Optimized TCDMA Structures Structures θ a β b ϕ c μ [D] μ(s 1 ) d [D] e S 0 f S 0 58, , 5.3 0, 0 1.8, , , 8.2 0, 0 3.2, 3.5 LE e 53, , , 0 1.8, 2.0 ICT-Q f 90, , 1.3 0, 0 8.5, ICT-AQ f 88, , 0.6 0, 0 8.7, 8.7 a Amino twist angle (Figure 1). b Dihedral angle 180 -(C(4)C(3)C(2)C(9)), measuring the out-of-plane character of the ortho cyano groups (Figure 1). c Pyramidal angle of the amino group (Figure 1). d Experimental dipole moment of the lowest excited singlet state S 1 (Table 7). e RASSCF(18,7+4+7)[2,2] and CASSCF(4,4). f RASSCF(20,7+5+7)[2,2] and CASSCF(6,5). RASSCF values in normal font, CASSCF data in italics. TABLE S4: Selected Angles and Dipole moments of the Optimized TCA Structures Structures θ a β b ϕ c μ [D] μ(s 1 ) d [D] S 0 0, 0 0.2, , , 2.1 LE,ICT-AQ 0, 0 0.0, 0.0 0, 0 2.8, ICT-Q 90, , 1.4 0, 0 7.1, 7.0 a Amino twist angle (Figure 1). b Dihedral angle 180 -(C(4)C(3)C(2)C(9)), measuring the out-of-plane character of the ortho cyano groups (Figure 1). c Pyramidal angle of the amino group (Figure 1). d Experimental dipole moment of the lowest excited singlet state S 1 (Table 7). RASSCF values in normal font, CASSCF data in italics. 22