TY - JOUR
T1 - Electronic and vibronic contributions to two-photon absorption in donor-acceptor-donor squaraine chromophores
AU - Ohira, Shino
AU - Rudra, Indranil
AU - Schmidt, Karin
AU - Barlow, Stephen
AU - Chung, Sung Jae
AU - Zhang, Qing
AU - Matichak, Jon
AU - Marder, Seth R.
AU - Bredas, Jean-Luc
PY - 2008/12/8
Y1 - 2008/12/8
N2 - Many squaraines have been observed to exhibit two-photon absorption at transition energies close to those of the lowest energy one-photon electronic transitions. Here, the electronic and vibronic contributions to these low-energy two-photon absorptions are elucidated by performing correlated quantum-chemical calculations on model chromophores that differ in their terminal donor groups (diarylaminothienyl, indolenylidenemethyl, dimethylaminopolyenyl, or 4-(dimethylamino)phenylpolyenyl). For squaraines with diarylaminothienyl and dimethylaminopolyenyl donors and for the longer examples of 4-(dimethylamino) phenylpolyenyl donors, the calculated energies of the lowest two-photon active states approach those of the lowest energy one-photon active (1Bu) states. This is consistent with the existence of purely electronic channels for low-energy two-photon absorption (TPA) in these types of chromophores. On the other hand, for all squaraines containing indolinylidenemethyldonors, the calculations indicate that there are no low-lying electronic states of appropriate symmetry for TPA. Actually, we find that the lowest energy TPA transitions can be explained through coupling of the one-photon absorption (OPA) active 1Bu state with bu vibrational modes. Through implementation of Herzberg-Teller theory, we are able to identify the vibrational modes responsible for the low-energy TPA peak and to reproduce, at least qualitatively, the experimental TPA spectra of several squaraines of this type.
AB - Many squaraines have been observed to exhibit two-photon absorption at transition energies close to those of the lowest energy one-photon electronic transitions. Here, the electronic and vibronic contributions to these low-energy two-photon absorptions are elucidated by performing correlated quantum-chemical calculations on model chromophores that differ in their terminal donor groups (diarylaminothienyl, indolenylidenemethyl, dimethylaminopolyenyl, or 4-(dimethylamino)phenylpolyenyl). For squaraines with diarylaminothienyl and dimethylaminopolyenyl donors and for the longer examples of 4-(dimethylamino) phenylpolyenyl donors, the calculated energies of the lowest two-photon active states approach those of the lowest energy one-photon active (1Bu) states. This is consistent with the existence of purely electronic channels for low-energy two-photon absorption (TPA) in these types of chromophores. On the other hand, for all squaraines containing indolinylidenemethyldonors, the calculations indicate that there are no low-lying electronic states of appropriate symmetry for TPA. Actually, we find that the lowest energy TPA transitions can be explained through coupling of the one-photon absorption (OPA) active 1Bu state with bu vibrational modes. Through implementation of Herzberg-Teller theory, we are able to identify the vibrational modes responsible for the low-energy TPA peak and to reproduce, at least qualitatively, the experimental TPA spectra of several squaraines of this type.
KW - Chromophores
KW - Nonlinear optics
KW - Squaraines
KW - Two-photon absorption
KW - Vibronic coupling
UR - http://www.scopus.com/inward/record.url?scp=57149146880&partnerID=8YFLogxK
U2 - 10.1002/chem.200801055
DO - 10.1002/chem.200801055
M3 - Article
C2 - 18972462
AN - SCOPUS:57149146880
SN - 0947-6539
VL - 14
SP - 11082
EP - 11091
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
IS - 35
ER -