Theoretical study of the valence π → π * excited states of polyacenes: anthracene and naphthacene

Abstract

The valence p ® p* excited states of anthracene and naphthacene are studied with multireference perturbation theory with complete active space selfconsistent ®eld reference functions. The predicted spectra provide a consistent assignment of all one-and twophoton spectra and T-T spectra of low-lying valence p ® p* excited states of anthracene and naphthacene. The present theory predicts the valence p ® p* excitation energies with an accuracy of 0.15 eV for anthracene and of 0.25 eV or better for naphthacene. The excited states of anthracene and naphthacene are compared with those of benzene and naphthalene studied previously. The present calculations predict that, going from anthracene to naphthacene, there is a symmetry reversal of the two lowest singlet state transitions, but not for the triplet, just as indicated by the experimental data. Some general trends of polyacene excited states are discussed based on the calculated results for benzene to naphthacene. Conclusive results obtained for anthracene and naphthacene can be used as a model for understanding the excited states of larger polyacenes.

A benchmark theoretical study of the electronic ground state and of the singlet-triplet split of benzene and linear acenes

“…In this particular case, B3LYP bond lengths are within 0.02 Å of the values obtained by means of x-ray crystallographic studies of benzene and acenes ͑see Ref. 38 for a detailed comparison of B3LYP data with experimental structures͒.…”

“…For instance, results obtained for naphthalene using the cc-pVXZ ͑X=D,T͒ basis sets demonstrate that the +CCSD ͓+CCSD͑T͔͒ corrections to the MP4SDQ ͓CCSD͔ values for the ST gaps have converged below 1 kcal/mol with regard to the basis set when X = D. Basis set extrapolations employing triple-, quadruple-, and quintuple-zeta basis yield slight increases, of the order of one-fourth of a kcal/mol only, of the singlet-triplet gaps obtained at the MP2 level, compared to extrapolations made using smaller basis sets. 38 an observation which sheds light on rather serious shortcomings in the latter study with regards to the employed CASSCF geometries, as well as in the -valence ͑12,12͒ TABLE VII. FPA of the vertical singlet-triplet gaps of benzene ͑all energies and corrections are given in kcal/mol͒.…”

“…36 Heptacene can also be synthesized in the same matrix ͑under an inert atmosphere͒, where it can be maintained only up to 4 h; 37 no one has ever managed to measure the ST gap of this compound so far. Except for multireference MRMP2/cc-pVDZ, 38 CASCI/cc-pVDZ or CASCI/STO-3G studies 13 on systems as large as naphthacene, hexacene, or dodecacene, respectively, most theoretical determinations of oligo-and polyacenes are the result of calculations employing empirical ͑Hückel͒ 8 or semiempirical ͑Parr-Pariser-Pople͒ Hamiltonians, 9,39 Density Functional Theory ͑DFT͒, 12,14 or Time-Dependent DFT ͑TDDFT͒. 40 In spite of the fast convergence of results toward the size of the basis set, the accuracy of DFT or TDDFT calculations of excited states will always necessarily be limited by the approximate nature of the employed exchange-correlation functionals.…”

Electronic spectral and photophysical properties of some p-phenylenevinylene oligomers in solution and thin films

“…With the compound EHOPV3PA, the fluorescence emission spectrum when obtained with excitation at 255 nm (corresponding to the S 0 ! S 4 anthracene transition [30]) did not display the characteristic emission band of anthracene, supporting the idea of efficient energy transfer from the anthracene (terminal groups) to the oligomer backbone.…”

Singlet fission in pentacene through multi-exciton quantum states

“…This method accounts for a quantum state's dynamic correlation by applying a secondorder perturbation to a complete-active-space wavefunction (CASSCF) and is similar to the CASPT2 method 33 . MRMP has been shown to be accurate for excitation energies calculated using a triple zeta basis set 34 and has in fact served as a benchmark for excitation energies 35,36 . Importantly, MRMP is one of the few methods capable of accurately describing ME states.…”