Birmingham have signed Brentford winger Jota for a club-record fee in excess of £6m, plus Bees team-mate Maxime Colin for an undisclosed fee and ex-Blackburn Rovers midfielder Jason Lowe.
Jota, 26, and full-back Colin, 25 have both signed four-year deals.
Birmingham have signed three Brentford players this summer, with Spaniard Jota and Frenchman Colin joining centre-back Harlee Dean at St Andrew's.
Lowe, 25, has signed a one-year deal, having left Rovers in May.
He had been on trial at Premier League side West Brom but was not offered a deal.
Lowe, who captained Rovers, played 196 games and scored once after progressing through the academy but left after their relegation from the Championship in May.
Harry Redknapp has also added 19-year-old Everton midfielder Liam Walsh on loan until 3 January - his 14th, and final, summer signing.
Meanwhile, Blues have loaned German midfielder Robert Tesche, 30, to Bundesliga 2 side VFL Bochum and left-back Cheick Keita, 20, to Serie A side Bologna for the season.
A new record
Blues' previous club-record signing was the £6m paid to Valencia for Serbian striker Nikola Zigic in May 2010.
The reported transfer fee was more than that when Emile Heskey signed from Liverpool in May 2004, but the final instalment was waived when Blues were relegated in 2006 - and he ended up costing only £4.75m.
Blues moves on deadline day
In - Jason Lowe (free agent), Jota (£6m from Brentford), Maxime Colin (undisclosed fee from Brentford), Liam Walsh (loan until January from Everton)
Out - Cheick Keita (loan to Bologna), Dan Scarr (loan to Wycombe), Robert Tesche (loan to Bochum), Clayton Donaldson (undisclosed to Sheff Utd), Maikel Kieftenbeld (undisclosed to Derby)
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