A 25-year-old Dublin man who groomed a teenage girl online has been jailed for six-and-a-half years for defilement and sexual exploitation.

The Central Criminal Court heard that Darragh Meehan, from Dargle Wood, Knocklyon in Dublin, was 19 when he met a 13-year-old girl and began contacting her through Facebook, Skype and by text message.

He performed sexual acts during Skpe contact and invited her to do the same.

He later met the girl in person and engaged in a sexual act with her.

The crimes were uncovered when the girl's mother found disturbing messages on her computer and reported it to gardaí.

Meehan pleaded guilty last month to one charge of defilement of a child and three charges of sexual exploitation between December 2011 and May 2012.

In a victim impact statement, the girl said at the time of the offences she had been going through a tough time and felt low in herself.

He became someone she confided in and made her feel special. She said he used her vulnerability to get what he wanted.

Mr Justice Patrick McCarthy said the repeated conduct fell firmly into the category of grooming and that Meehan had a degree of success with it.

He said while the girl did not physically resist, this was not true consent. Instead, she had been induced  to submit because of the grooming that had occurred.

The judge said he took into account character references from the man's friends, family and employer and accepted he was unlikely to reoffend and could be rehabilitated.

He could not give him full credit for his guilty plea because it came late in the day, about two weeks before he was due to go on trial.

The judge said the punitive element of the sentence had to be significant and imposed a six-and-a-half year sentence.

Meehan will also be registered as a sex offender.

At a sentence hearing last month, the court was told the now 19-year-old woman said in her victim impact statement that she was angry and upset at what had happened and just wanted to forget about it.

She said people told her at the time that it was not her fault but she could not see it.

"It was something that happened to me, not something I made happen," she said.

The woman said she had been in a bad place at the beginning of this process but now felt stronger and was hopeful her quality of life would continue to improve.

Defence counsel Sean Gillane said his client had not come to any further attention in the six years since the offences.

He said the separation of his client's parents when he was young had resulted in considerable personal difficulties for him.

In his early teens, he began spending increasing amounts of time alone in his bedroom seeking engagement and escape through the online world.

Mr Gillane submitted that the offences did not involve a contrived or sophisticated targeting of an individual as in similar cases in the past.

He said the offences had taken place within a narrow time frame.

He said both parties had been upfront about who they were and asked the court to place emphasis on this.

He said the accused man had been the adult but was still relatively young at the time.

He said now, as a 25-year-old, his client had developed considerable insight into the offences.

Mr Gillane said the accused man had written a letter of apology to the victim in which he indicated he had hurt her in a way she should not have been hurt.

He accepted that what he did was wrong and was "wholeheartedly sorry" for it and the abuse of her trust.