Mark McKenna, 38, from Northfleet, in Kent, pleaded guilty to arranging the commission of a child sex offence at Maidstone Crown Court last month.
He was arrested near a car park at the Bluewater shopping centre in August.
He had thought he was meeting the girl after sending her explicit messages online, but in fact had been talking to the vigilante group, The Hunted One.
The group had tipped off Kent Police and filmed his arrest after creating a fake Instagram account.
It describes itself as "a secret organisation of dedicated parents, pro-actively seeking out and exposing online groomers, sexual predators and paedophiles".
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During a series of exchanges over three-and-a-half weeks with the fictitious girl, McKenna sent explicit photos, a video and countless messages.
In one, he asked: "Can you kiss?"
When she replied yes, he said: "What else can you do?"
The court heard it was made clear from the outset she was 11 years old.
McKenna arranged to meet the girl at Bluewater on 6 August as his "girlfriend was away", sending her a photo of an unopened packet of condoms with the message "I have them".
He told her: "You do know I'm 38?
"You will have to be my daughter for the day," adding that she should not tell anyone in case he got in trouble with the police.
However, when he arrived at the shopping centre he was confronted by members of the vigilante group.
Sentencing, Judge Philip Statman described McKenna's behaviour as "abhorrent".
"You have succeeded in destroying your family," he said.
The judge told the court he was aware of how the case had unfolded, saying: "Matters of this kind ought properly to be left to the appropriate investigating police officers who are there to safeguard the interests of the community as a whole."
McKenna was placed on the sex offenders' register for life.

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30 March 2014 Last updated at 13:54 BST
The remains may be part of a massive emergency burial pit where thousands of plague victims were left 600 years ago.
Lead archaeologist Jay Carver says the find "solves a 660-year-old mystery".
"This discovery is a hugely important step forward in documenting and understanding Europe's most devastating pandemic," he said.

The Zimbabwean hit 10 boundaries in his 207-ball knock before he was lbw to left-arm spinner Jack Leach (3-77).
Leach earlier bowled England batsman James Vince for a third-ball duck as the visitors struggled to 92-4.
Ryan McLaren, though, scored 61 as he and Ervine added 118, while Lewis McManus was 41 not out at the close.
Hampshire are second from bottom of the table but defeated Nottinghamshire in their last outing, while Somerset are fifth, 35 points behind leaders Middlesex.
Lewis Gregory struck the first blow for the home side by bowling Jimmy Adams in the fourth over of play.
Will Smith and Vince followed in successive overs as Somerset wasted no time in bringing their two spinners, Leach and Roelof van der Merwe, into the attack.
Paceman Craig Overton was awarded his county cap during the lunch interval but went through the day wicketless, and it was Leach ended the partnership between Ervine and McLaren by having the latter caught by Tom Abell at short leg.
Hampshire all-rounder Sean Ervine told BBC Radio Solent:
"We looked at the wicket and we all saw it was going to spin.
"They bowled well up front and obviously the partnership with Ryan McLaren was hugely important and great for us.
"He played very well and was a bit unlucky - it was a great catch at short leg.
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A man confronted by vigilantes after arranging to meet an 11-year-old girl for sex has been jailed for five years.
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