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Pariser-Parr-Pople Model Based Investigation of Ground and Low-Lying Excited States of Long Acenes

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Title Pariser-Parr-Pople Model Based Investigation of Ground and Low-Lying Excited States of Long Acenes
 
Creator CHAKRABORTY, H
SHUKLA, A
 
Subject ORGANIC ELECTRONICS
LARGER ACENES
HEPTACENE
PHOTOGENERATION
POLYACETYLENES
HYDROCARBONS
ABSORPTION
OCTACENE
HEXACENE
NONACENE
 
Description Several years ago, Angliker et al. [Chem. Phys. Lett. 1982, 87, 208] predicted nonacene to be the first linear acene with the triplet state 1(3)B(2u) as the ground state, instead of the singlet 1(1)A(z) state. However, contrary to that prediction, in a recent experimental work, Tonshoff and Bettinger [Angew. Chem. Int. Ed. 2010, 49, 4125] demonstrated that nonacene has a singlet ground state. Motivated by this experimental finding, we decided to perform a systematic theoretical investigation of the nature of the ground and the low-lying excited states of long acenes, with an emphasis on the singlet-triplet gap, starting from naphthalene, all the way up to decacene. The methodology adopted in our work is based upon the Pariser-Parr-Pople model (PPP) Hamiltonian, along with the large-scale multireference singles-doubles configuration interaction (MRSDCI) approach. Our results predict that even though the singlet-triplet gap decreases with the increasing conjugation length, nevertheless, it remains finite till decacene, thus providing no evidence of the predicted singlet-triplet crossover. We also analyze the nature of many-particle wave function of the correlated singlet ground state and find that the longer acenes exhibit a tendency toward an open-shell singlet ground state. Moreover, when we compare the experimental absorption spectra of octacene and nonacene with their calculated singlet and triplet absorption spectra, we observe excellent agreement for the singlet case. Hence, the optical absorption results also confirm the singlet nature of the ground state for longer acenes. Calculated triplet absorption spectra of acenes predict two well-separated intense long-axis polarized absorptions, against one such peak observed for the singlet case. This is an important prediction regarding the triplet optics of acenes, which can be tested in future experiments on oriented samples.
 
Publisher AMER CHEMICAL SOC
 
Date 2014-10-17T04:15:53Z
2014-10-17T04:15:53Z
2013
 
Type Article
 
Identifier JOURNAL OF PHYSICAL CHEMISTRY A, 117(51)14220-14229
http://dx.doi.org/10.1021/jp408535u
http://dspace.library.iitb.ac.in/jspui/handle/100/15924
 
Language en