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Theoretical study on oligothiophene N-succinimidyl esters: size and push-pull effects.
M Piacenza1, M Zambianchi, G Barbarella
1National Nanotechnology Laboratory of CNR-INFM, Distretto Tecnologico ISUFI, Università del Salento, Via per Arnesano, I-73100, Lecce, Italy. manuelpiacenza@gmail.com
Physical Chemistry Chemical Physics : PCCP
|September 4, 2008
Summary
Functionalizing bithiophene and terthiophene N-succinimidyl esters with a methylsulfanyl group shifts their optical properties. Alpha-substituted compounds exhibit significant red-shifts and larger Stokes-shifts compared to beta-substituted ones.
Area of Science:
- Organic chemistry
- Computational chemistry
- Photophysics
Background:
- Oligothiophenes are crucial in organic electronics.
- Functionalization impacts their optical and electronic properties.
- N-succinimidyl esters offer tunable characteristics.
Purpose of the Study:
- To theoretically investigate the optical properties of methylsulfanyl-functionalized bithiophene and terthiophene N-succinimidyl esters.
- To compare the effects of alpha- versus beta-substitution on these properties.
- To evaluate the accuracy of TD-DFT and RI-CC2 methods for these systems.
Main Methods:
- Theoretical study using time-dependent density functional theory (TD-DFT).
- Approximate coupled-cluster singles and doubles with resolution of identity (RI-CC2) calculations.
- Analysis of ground and excited state properties, including absorption and fluorescence spectra.
Main Results:
- RI-CC2 calculations showed better agreement with experimental absorption and fluorescence energies than TD-DFT.
- Alpha-substitution led to a significant red-shift in absorption and fluorescence bands and increased Stokes-shift.
- Beta-substitution effects were less pronounced; alpha-substituted compounds had larger Stokes-shifts due to a more planar excited-state conformation.
Conclusions:
- The position of methylsulfanyl group functionalization (alpha vs. beta) critically influences the optical properties of bithiophene and terthiophene N-succinimidyl esters.
- RI-CC2 is a more reliable method for predicting optical properties in these systems compared to TD-DFT, especially for beta-substituted compounds.
- The enhanced Stokes-shift in alpha-substituted derivatives is attributed to favorable excited-state molecular geometry.
