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. 2017 May 4;2(5):1795-1803.
doi: 10.1021/acsomega.7b00278. eCollection 2017 May 31.

Singlet and Triplet Excited State Energy Ordering in Cyclopenta-Fused Polycyclic Aromatic Hydrocarbons (CP-PAHs) Suitable for Energy Harvesting: An Exact Model and TDDFT Study

Sumit Naskar  1 , Mousumi Das  1
Affiliations

Singlet and Triplet Excited State Energy Ordering in Cyclopenta-Fused Polycyclic Aromatic Hydrocarbons (CP-PAHs) Suitable for Energy Harvesting: An Exact Model and TDDFT Study

Sumit Naskar et al. ACS Omega. .

Abstract

We calculated the ground and low-lying excited states of cyclopenta-fused polycyclic aromatic hydrocarbons (CP-PAHs) using exact diagonalization in full configuration interaction (CI) within the model Pariser-Parr-Pople Hamiltonian as well as a time-dependent density functional theory technique. The CP-PAHs include acenapthylene, isomers of pyracylene, cycloocta-pentalene, and three isomers of dicyclo-pentacyclo-octenes (DCPCO). We used the inherent symmetries of these systems to calculate the energy ordering of the lowest singlet (S1) and lowest triplet excited (T1) states with respect to the ground state (S0). The calculation shows that the lowest dipole allowed singlet absorption varies from 0.43 to 1.42 eV for most of these systems. Such an optical absorption range is very promising in harvesting solar radiation ranging from the visible to near-infrared region improving the efficiency of photovoltaic device application. The calculated optical gaps for pyracylene, acenapthylene, and two isomers of DCPCO are in very good agreement with experimental results reported in the literature. The calculated S1-T1 energy gaps (ΔST) in cycloocta-pentalene and in the DCPCO isomers are very small ranging from 0.01 to 0.2 eV, which is highly desirable in improving their electroluminescence efficiency in light-emitting device applications.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Geometries of acenapthylene (a), pyracylene (b), cyclopenta-acenapthylene (c), and isomers of dicyclo-pentacyclo-octenes (DCPCO) (d–f), and cycloocta-pentalene (COP) (g).
Figure 2
Figure 2
Low-lying energy ordering obtained using the PPP model Hamiltonian method in the singlet and triplet subspaces of acenapthylene (a), pyracylene (b), and cyclopenta-acenapthylene (c), respectively.
Figure 3
Figure 3
Low-lying energy ordering obtained using the PPP model Hamiltonian method in the singlet and triplet subspaces of isomers of dicyclo-pentacyclo-octenes (DCPCO) (d), (e), (f), and cycloocta-pentalene (COP) (g), respectively.
Figure 4
Figure 4
Comparison of optical and ΔST gap as a function of D–A strength (|ϵ|) for acenapthylene.
Figure 5
Figure 5
Variation of optical and ΔST gap as a function of D–A strength (|ϵ|) for pyracylene (b) and cyclopenta-acenapthaylene (c).
Figure 6
Figure 6
Variation of optical and ΔST gap as a function of D–A strength (|ϵ|) for DCPCO isomers (d), (e), (f), and cycloocta-pentalene (g).
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