Roberto Cardia

Effects of TIPS-Functionalization and Perhalogenation on the Electronic, Optical, and Transport Properties of Angular and Compact Dibenzochrysene

We report a systematic comparative study on dibenzo[b,def]chrysene (angular) and dibenzo[def,mno] chrysene (compact) polyaromatic hydrocarbons and their bis-triisopropylsilylethynyl (TIPS)-functionalized and perhalogenated (F, Cl) counterparts. We used density functional theory (DFT) and time-dependent DFT to quantify the effects of morphology and chemical modifications on the electronic, optical, and transport properties. In particular, we compared electron affinity, ionization energy, fundamental gap, optical absorption, exciton binding energy, and reorganization energies for holes and electrons. For both TIPS-functionalization and halogen substitutions, we found larger electron affinities (nearly tripled with perchlorination). Ionization energies are found to be reduced for TIPS-functionalization (by ∼5%) and enhanced following halogen substitution (up to 17%). In both compact and angular dibenzochrysenes, the above trends reflect in a general reduction of the fundamental gap (up to 22%) following chemical modification. The effect of perhalogenation and TIPS-functionalization is always to increase molecular reorganization energies for both holes and electrons. Concerning the optical properties, we observe a redshift of the optical onset in all cases; for TIPS-functionalized molecules, in particular, we additionally found a remarkable enhancement of the absorption in the visible region.

Neutral-cluster implantation in polymers by computer experiments

In this work, we perform atomistic model potential molecular dynamics simulations by means of state-of-the art force-fields to study the implantation of a single Au nanocluster on a polydimethylsiloxane substrate. All the simulations have been performed on realistic substrate models containing up to ∼4.6 × 106 of atoms having depths up to ∼90 nm and lateral dimensions up to ∼25 nm. We consider both entangled-melt and cross-linked polydimethylsiloxane amorphous structures. We show that even a single cluster impact on the polydimethylsiloxane substrate remarkably changes the polymer local temperature and pressure. Moreover, we observe the presence of craters created on the polymer surface having lateral dimensions comparable to the cluster radius and depths strongly dependent on the implantation energy. Present simulations suggest that the substrate morphology is largely affected by the cluster impact and that most-likely such modifications favour the penetration of the next impinging clusters.

Deciphering Molecular Mechanisms of Interface Buildup and Stability in Porous Si/Eumelanin Hybrids

Porous Si/eumelanin hybrids are a novel class of organic–inorganic hybrid materials that hold considerable promise for photovoltaic applications. Current progress toward device setup is, however, hindered by photocurrent stability issues, which require a detailed understanding of the mechanisms underlying the buildup and consolidation of the eumelanin–silicon interface. Herein we report an integrated experimental and computational study aimed at probing interface stability via surface modification and eumelanin manipulation, and at modeling the organic–inorganic interface via formation of a 5,6-dihydroxyindole (DHI) tetramer and its adhesion to silicon. The results indicated that mild silicon oxidation increases photocurrent stability via enhancement of the DHI–surface interaction, and that higher oxidation states in DHI oligomers create more favorable conditions for the efficient adhesion of growing eumelanin.

Electronic and optical properties of chromophores from bacterial cellulose

We report a systematic computational investigation on the electronic and optical properties of the principal chromophores found in bacterial cellulose (BC). In particular, we focus on the three chromophoric leading structures that were isolated from aged BC (1) 2,5-dihydroxy-[1,4]benzoquinone (2) 5,8-dihydroxy-[1,4]naphthoquinone and (3) 2,5-dihydroxyacetophenone. For the isolated molecules we performed all-electrons density functional theory (DFT) and time dependent DFT calculations with a localized Gaussian basis set and the hybrid exchange correlation functional B3LYP. We quantified key molecular properties relevant as electron affinities, ionization energies, quasi-particle energy gaps, optical absorption spectra, and exciton binding energies. We address moreover the impact of the solvent on the optical properties of the above systems using starting configurations obtained after classical molecular dynamics simulations in water. Our results could be of importance to comprehend the mechanisms underlying the processes of degradation of BC, which are of fundamental relevance for cultural heritage applications.

Electronic and optical properties of functionalized polyaromatic hydrocarbons: a computational investigation on perfluorinated circumacenes

We report a systematic computational investigation on the electronic and optical properties of some representive polyaromatic hydrocarbons of interest for solid-state applications. We focus in particular on the five first members of the circumacenes family (i.e., coronene, ovalene, circumanthracene, circumtetracene, and circumpentacene). For the isolated gas-phase molecules we performed all-electrons Density Functional Theory (DFT) and Time Dependent DFT (TDDFT) calculations with a localized Gaussian basis-set and the hybrid exchange-correlation functional B3LYP. We quantified the effect of the complete substitution of peripheral hydrogen atoms with fluorine atoms for a series of key molecular properties relevant for molecular electronics and photonics: electron affinities, ionization energies, quasi-particle energy-gaps, optical absorption spectra, and exciton binding energies. We discuss the possible implications of the general trends observed with respect to both fundamental research and opto-electronic applications.

Vibrational and optical characterization of s-triazine derivatives

The optical and electron properties of three different s-triazine derivatives are investigated to ascertain the role of the donor acceptor character in amine-triazine systems depending on the bridging radical of the ammine group. The three derivatives were obtained starting from three different ammine compounds allowing to achieve a structure with a triazine core, surrounded by three ammine group and terminated with cyano or methyl or oxy-methyl functional group. Experimental optical data were interpreted in view of the electronic insights gathered by means of density functional theory simulations on base compounds. As compared to the reference electron donating triazine core, the resulting compounds show different donor acceptor character, from electron accepting to electron donating feature. Among the analyzed derivatives, the cyano terminated ammino-triazine compound shows the most promising optical features for photonics and lighting applications.