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Two‐Photon Absorption in Quadrupolar π‐Conjugated Molecules: Influence of the Nature of the Conjugated Bridge and the Donor–Acceptor Separation
Author(s) -
Zojer Egbert,
Beljonne David,
Pacher Peter,
Brédas JeanLuc
Publication year - 2004
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200305650
Subject(s) - conjugated system , chromophore , polyene , cyanine , acceptor , two photon absorption , chemistry , absorption (acoustics) , ground state , photochemistry , materials science , atomic physics , physics , organic chemistry , polymer , optics , fluorescence , laser , composite material , condensed matter physics
Quadrupolar‐type substitution of π‐conjugated chromophores with donor and acceptor groups has been shown to increase their two‐photon absorption (TPA) response by up to two orders of magnitude. Here, we apply highly correlated quantum‐chemical calculations to evaluate the impact of the nature of conjugated bridge and the charge‐transfer distance on that enhancement. We compare chromophores with phenylenevinylene‐, thienylenevinylene‐, polyene‐, and indenofluorene‐type backbones substituted by dimethylamino and cyano groups. In all compounds, we find a strongly TPA‐active A g state (either 2A g or 3A g ) in the low‐energy region, as well as a higher lying TPA‐active state (mA g ) at close to twice the energy of the lowest lying one‐photon allowed state; the smaller energy detuning in the mA g states results in very large TPA cross sections δ . We also investigate the influence of the degree of ground‐state polarization on TPA. Independent of the nature of the backbone and the donor–acceptor separation, δ displays the same qualitative evolution with a maximum before the cyanine‐like limit; the highest TPA cross sections are calculated for distirylbenzene‐ and polyene‐based systems.