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A Theoretical Study on the Low‐Lying Excited States of 2,2′:5′,2′′‐Terthiophene and 2,2′:5′,2′′:5′′,2′′′‐Quaterthiophene
Author(s) -
Rubio Mercedes,
Merchán Manuela,
Ortí Enrique
Publication year - 2005
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200400487
Subject(s) - intersystem crossing , terthiophene , excited state , singlet fission , singlet state , conrotatory and disrotatory , ab initio , chemistry , degenerate energy levels , molecular physics , computational chemistry , physics , atomic physics , quantum mechanics , molecule , ring (chemistry) , organic chemistry
The nature and properties of the low‐lying singlet and triplet valence excited states of 2,2′:5′,2′′‐terthiophene (terthiophene) and 2,2′:5′,2′′:5′′,2′′′‐quaterthiophene (tetrathiophene) are discussed on the basis of high‐level ab initio computations. The spectroscopic features determined experimentally for short α‐oligothiophenes are rationalised on theoretical grounds. Special attention is devoted to the nonradiative decay process through intersystem crossing (ISC) from the singlet to the triplet manifold, which is known to be relatively less efficient in tetrathiophene. Along the geometry relaxation of the S 1 state of terthiophene, the S 1 and T 2 states become degenerate, which leads to a favourable situation for the occurrence of ISC. The parallel process is expected to be less favoured in tetrathiophene because of the less efficient spin–orbit coupling and the increase of the S 1 –T 2 energy gap.