Abstract
In this contribution, we examine the photophysical properties of 15 totally trans-trans 1,4-distyrylbenzene derivatives (DSBs) functionalized with different electron-donating (ED) and electron-withdrawing (EW) groups by experimental and computational methodologies. We use UV-vis and fluorescence spectroscopies to determine the experimental optical properties such as the maximum absorption (λabsexp) and emission (λemexp) wavelengths, the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gaps (ΔEabsexp), the molar extinction coefficients (ε), the fluorescence quantum yields (Φf), and the fluorescence lifetimes (τ). We also calculate the experimental spontaneous emission decay rate (krexp) and correlate all of these magnitudes to the corresponding calculated properties, maximum absorption (λabscal) and emission (λemcal) wavelengths, vertical transition energies (ΔEabscal), oscillator strength (Fosc), and spontaneous emission decay rate (krcal), obtained by the time-dependent density functional theory method. We analyze the effect of the electronic nature of the substituents on the properties of the DSBs, finding that the ED and EW groups lead to bathochromic shifts. This is consistent with the decrease of ΔE values as the strength of ED and EW substituents increases. We find excellent correlations between calculated and experimental values for λabs, λem, and ΔEabs (r ∼ 0.99-0.95). Additionally, the correlations between the relative ε with Fosc values and the kr values are in good agreement (r ∼ 0.88-0.72) with the experimental properties. Overall, we find that for substituted 1,4-DSBs, computational chemistry is an excellent tool to predict structure-property relationships, which can be useful to forecast the properties of their polymeric analogues, which are usually difficult to determine experimentally.
Highlights
Poly(phenylenevinylene) (PPV) and its derivatives have attracted considerable attention because of their remarkable optical and electronic properties
It is well known that after the discovery of the optoelectronic properties of PPVs, especially the electroluminescence[1,2], these materials have been exploited as an active layer in organic light-emitting diodes (OLEDs)[3,4,5,6,7,8,9,10,11,12,13] and other applications such as laser dyes[14,15,16], photovoltaic cells[17,18,19,20,21,22,23], chemosensors[24,25,26,27,28,29], linkers for metalorganic frameworks (MOFs)[30,31,32], dendrimers[33,34,35,36], photoredox catalysts and photosensitizers[37,38,39]
A similar study reported by Chaieb et al, showed that the introduction of ED groups on the central ring of the DSB system leads to a red shift[45]
Summary
Poly(phenylenevinylene) (PPV) and its derivatives have attracted considerable attention because of their remarkable optical and electronic properties. OPVs share many properties with their structural analog PPVs, especially in the case of segmented polymers This is useful to determine which structural features of a PPV, or a segmented polymer, are the most appropriate to incorporate for a given application. This is known as “the oligomer approach”[41]. The study of the structural effects on the photophysical properties of DSBs provides insights into the structural features that a phenylenevinylene derivative (oligomer or polymer) must have to be useful. In order to understand better the structure-property relationships of this type of materials, here we correlate the experimental optical characterization of DSBs – substituted with different ED or EW groups (Figure 1) – with their optical properties calculated by computational methods based on the time-dependent DFT (TDDFT)
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