Photophysical properties of pyrrolobenzenes with different linking and substitution pattern: The transition between charge transfer states with large (MICT) and small (TICT) resonance interaction

The Influence of the π-Conjugated Spacer on Photophysical Properties of Difluoroboranyls Derived from Amides Carrying a Donor Group

A series of difluoroboranyls derived from amides carrying a variable π-conjugated spacer between the electron-donating (D) and electron-accepting (A) groups was synthesized and characterized with (1)H, (11)B, (13)C, (15)N, and (19)F NMR, electronic absorption, fluorescence spectroscopies, and first-principle calculations. The D-to-A distance in the series varied from 1.5 to 4.5 Å, causing bathochromic shifts of both the absorption and fluorescence maxima by more than 120 and 213 nm, respectively. These trends are rationalized by quantum-mechanical calculations that allow for quantification of the charge-transfer distance. Theoretical calculations were also performed to determine the vibronic couplings and thus to reproduce the experimental band shapes.

The driving forces for twisted or planar intramolecular charge transfer

The driving forces for twisting or planarization of excited D–A (donor–acceptor)-type chromophore have been investigated.

The effect of polyaromatic hydrocarbons on the spectral and photophysical properties of diaryl-pyrrole derivatives: an experimental and theoretical study

A new class of diaryl-pyrrole derivatives of the polyaromatic hydrocarbons (PAH) benzene, naphthalene, anthracene and pyrene were synthesized in a multicomponent reaction under microwave irradiation and studied in solution at room (293 K) and low (77 K) temperature. The study includes a complete spectroscopic evaluation (singlet-singlet and triplet-triplet absorption, fluorescence and phosphorescence spectra) as well as photophysical evaluation (fluorescence, phosphorescence and triplet lifetimes together with fluorescence and triplet occupation and singlet oxygen sensitization quantum yields). From the above evaluation, a complete set of deactivation rate constants (kF, kIC and kISC) could be obtained. The study was further complemented with TDDFT calculations. It is shown that, with the exception of the anthracene derivative, the diaryl-pyrrole moiety strongly influences the spectral and photophysical properties of the PAH and that with the exception of the benzene derivative, the excited state internal conversion deactivation channel of the diaryl-pyrrole derivatives is higher than that of the PAH counterparts.

Photophysical and complexation properties of benzenesulfonamide derivatives with different donor and acceptor moieties

Pyrrolobenzosulfonamide, indolobenzosulfonamide and carbazolobenzosulfonamide derivatives with different acceptor groups were synthesized and their photophysical properties were compared. The electron donor linking sites are found to influence the emission characteristics of these compounds while acceptor linking sites have no noticeable effects on the spectral properties. P2-A5 which is a C-C linked pyrrole derivative exhibited different spectral properties from the C-N linked pyrrole derivatives. The complexation properties of the molecules were also investigated employing Na (I), Ca (II), Li (I), Mg (II), Zn (II) and Cu (II) ions.

Ultrafast relaxation and coherent oscillations in aminobenzonitriles in the gas phase probed by intense-field ionization

4-Aminobenzonitrile derivatives have two excited states of similar energy: besides the benzene-like L(b) state (also termed "locally excited" or LE state) one with charge-transfer (CT) character that is slightly higher in the isolated molecules. The CT state can be lowered by solvents of suitable polarity, so that dual fluorescence can be observed in them. It is controversial along which coordinate this state is displaced, although the amino-group twist is a wide-spread assumption. We investigated a number of such compounds by transient ionization in the gas phase, initially exciting the higher-lying L(a) state (S(2)). Here we briefly review the previous results on 4-(dimethylamino)benzonitrile (the prototype of this class of molecules), 4-piperidino-, pyrrolidino- and pyrrolyl-benzonitrile and compare them with new results on 4-aminobenzonitrile and on the bridged derivative N-methyl-6-cyano-1,2,3,4-tetrahydroquinoline (NMC6). Although in the latter two molecules the CT state has never been detected before, we find the same relaxation path for all compounds: From S(2), the wave packet passes through a conical intersection (CI); from there part of it reaches the S(1) (L(b)) state directly, whereas another part temporarily populates the CT state (also in NMC6), from where it goes around the CI also to the L(b) well. The wave packet directly reaching the L(b) well oscillates there along coordinates involving amino-group twist and wagging or molecular arching and a quinoidal distortion. These coordinates must be components of the CI displacement vector. A vibration involving bond-length alternation of the benzene ring is ascribed to a momentum caused by the electronic symmetry change in the CI, i.e., to the nonadiabatic coupling vector. Also the CT state involves amino-group twist, as to conclude from the anisotropy of the corresponding signal. The six-membered aliphatic ring in NMC6 hinders the twist and raises the CT state to an energy that is, however, still below the L(a) state, so that it can be temporarily populated in a barrierless process. Also in aminobenzonitrile the CT state is between L(a) and L(b) and is reached from L(a) without a barrier. The twist is rationalized by vibronic interaction with a higher state that is pi-antibonding between the amino group and the aromatic ring.